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Regional differences in collagen stable isotope and tissue trace element profiles in populations of long-tailed duck breeding in the Canadian Arctic
Abstract
Adult long-tailed ducks (Clangula hyemalis) were collected from nine locations across their breeding grounds in northern Canada and measurements of stable isotopes of carbon (delta(13)C), nitrogen (delta(15)N) and sulfur (delta(34)S) in bone collagen were used to investigate if relative use of freshwater habitats such as the Great Lakes (with expected depleted stable isotope profiles) compared with coastal marine environments (with expected enriched stable isotope foodweb profiles) could explain tissue trace element profiles. Contrary to expectation, all three stable isotopes did not covary in our sample, suggesting that mechanisms other than simple freshwater vs. marine isotopic gradients were involved among populations. All three stable isotopes varied significantly with collection location and both delta(15)N and delta(13)C values varied significantly between sexes suggesting that males exploit either a different food base or occur in different geographic areas than females for at least part of the year. The delta(34)S data, in particular, suggested that many of the birds breeding in the western Canadian Arctic probably overwinter in the Great Lakes along with many of the birds breeding in Hudson Bay. Males at the majority of collection locations had higher concentrations of hepatic Hg (1.1-8 microg/g dw), Cu (25-40 mug/g dw), Se (7.3-27 mug/g dw) and renal Cd (33-129 microg/g dw) than females. Concentrations of Hg, Cu and Cd were well below toxicological threshold levels found in the literature. However, hepatic Se concentrations in 64% of the females exceeded 10 mug/g dw and concentrations in 8% of the birds measured exceeded 33 microg/g dw suggesting levels of potential concern.
... The ecology of marine birds is well studied, which has allowed documentation of patterns of Hg bioaccumulation across food webs and trophic levels (Campbell et al. 2005), and at different spatial and temporal scales (Braune 2007;Point et al. 2011). Such studies are possible because marine birds are abundant, widespread, and part of planned sustainable harvests allowing for relatively easy and ethical sampling to occur (Braune et al. 2005). Importantly, studies of marine birds offer a number of useful endpoints, including reproductive output in relation to Hg burden at the individual level to changes in demography over periods of decades (Mallory and Braune 2012). ...
... In the Canadian Arctic, nine marine bird species have been studied for Hg concentrations at varying spatial and temporal scales: Arctic tern, glaucous gull (Larus hyperboreus), ivory gull (Pagophila eburnea), black guillemot (Cepphus grylle), black-legged kittiwake (Rissa tridactyla), common eider, long-tailed duck (Clangula hyemalis), northern fulmar (Fulmarus glacialis), and thick-billed murre Braune et al. 2005; Mallory and Braune 2012). These species represent overlapping but different geographical areas and occupy a variety of niches within Arctic food webs making them ideal for examining questions about Hg within the Canadian Arctic marine ecosystem (Mallory and Braune 2012). ...
Mercury (Hg) is a naturally occurring trace element that is also a by-product of anthropogenic activities and, in its methylated form, it is a neurotoxin that can have adverse effects on wildlife. The toxicity of Hg for humans, wildlife, and ecosystem health merits monitoring of its concentrations by various sampling means. Marine birds are widely used as indicators of ecosystem health, including biomonitoring of Hg in the Arctic. Since the mid-1970s, Hg concentrations in marine birds have been monitored across the Canadian North. Current Hg burdens in most northern marine bird species are below levels associated with health concerns, but several species have concentrations that are at or near levels associated with impaired reproduction. Arctic marine birds in Canada may be particularly at risk from increasing Hg levels associated with changing climatic conditions and long-term Hg deposition patterns. Research on marine birds should, therefore, continue to focus on spatial and temporal patterns of Hg contamination, assessing levels and biological effects in species that are experiencing high concentrations, and among species that are widely harvested due to the possible implications for human health.
... The δ 15 N values for the feathers of Long-tailed Ducks from the Lithuanian Baltic Sea coastal zone ranged from 7.7 to 13.9‰. A very similar range of these signatures have been published by Braune et al. (2005) who measured stable isotopes in bone collagen of Long-tailed Ducks in their breeding grounds. Bone collagen is low metabolic rate tissues which represent lifetime average values (Braune et al., 2005) while feathers represent bird diet of their growth period (Mizutani et al., 1990). ...
... A very similar range of these signatures have been published by Braune et al. (2005) who measured stable isotopes in bone collagen of Long-tailed Ducks in their breeding grounds. Bone collagen is low metabolic rate tissues which represent lifetime average values (Braune et al., 2005) while feathers represent bird diet of their growth period (Mizutani et al., 1990). The δ 13 C values of Long-tailed Ducks ranged from –33.6 to –24.9‰ showing variation of feeding habitats – from freshwater to marine environment. ...
The stable isotopes of nitrogen (δ15N) and carbon (δ13C) were analysed in the feathers of the Great Cormorant (Phalacrocorax carbo), Grey Heron (Ardea cinerea) and Long-tailed Duck (Clangula hyemalis) staying in the different seasons at the Lithuanian Baltic Sea coast. Stable isotope ratios in bird feathers represented dietary variations and foraging habitats during the feather growth period. Adult Great Cormorants fed juveniles by smaller fish at the beginning of fledging, switching later to larger prey. The stable isotope analysis indicated that the Grey Heron diet did not change significantly during the fledging period of their juveniles. The calculated trophic levels of Great Cormorants and Grey Herons were similar (3.55 ± 0.12 and 3.57 ± 0.41, respectively). The isotopic values in Grey Herons and Great Cormorants were 14.6–16.0‰ for δ15N and –27.3–(–24.9)‰ for δ13C. These values are typical of piscivorous bird species mostly feeding in fresh-water bodies, i. e. in the Curonian Lagoon. The δ15N values found in the feathers of Long-tailed Ducks ranged from 7.7 to 13.9‰ and the δ13C values ranged from –33.6 to –24.9‰ showing high variation of feeding habitats during the moulting period: from freshwater to marine environment.
... Some of the longer-term (breeding season) effects of selenium may be ruled out to some extent since depuration or cleansing of some toxins has been shown to occur by the time waterfowl arrive on their breeding grounds in Canada and Alaska (pers. comm., Christine Custer, USGS), but other effects from this or other toxins may be ongoing or incompletely understood, and may have long-term impacts on diving duck species and other waterbird taxa (Braune 2005, Franson et al. 2011, Outridge et al.1999, Sea Duck Joint Venture 2015. ...
We visually surveyed wintering water-fowl at nine locations in the Milwaukee Estuary and Harbor during the winter of 2016-2017. We recorded numbers of species and individuals found, and discuss factors possibly influencing the abundance of wintering waterfowl within the Estuary and Harbor. Large numbers of wintering waterfowl were found except during relatively brief periods of extensive ice cover. Fourteen waterfowl species were recorded, with the most common being Greater Scaup and least common being Ross's Goose and White-winged Scoter. We developed a checklist for wintering water-fowl species with conservation status rankings and summarizing habitat needs. Wintering waterfowl populations may be affected by sublethal levels of chemical contaminants within the sediments of the Estuary and Harbor. Maintaining high water quality and restricting boat traffic in winter are recommended for the long-term health of wintering waterfowl populations in the area. Additionally, two species of inva-sive Dreissenid mussels have become a major food resource for many diving duck species, raising some concerns and a need for more research.
... Microbial activity facilitates methylation of monomethylmercury (MeHg), which particularly bioaccumulates in tissues of organisms (Hammerschmidt and Fitzgerald, 2006;Mason et al., 2012), and is biomagnified along the food chain (Jaeger et al., 2009;Lavoie et al., 2013;Ruus et al., 2015). As a result, Hg concentrations have increased over time in multiple Arctic species (Braune et al., 2005(Braune et al., , 2015Dietz et al., 2006aDietz et al., , 2006bDietz et al., , 2009Dietz et al., , 2011Dietz et al., 2021;Rigét et al., 2011) reaching especially high levels in Arctic high-trophic species such as polar bears (Ursus maritimus; Dietz et al., 1998Dietz et al., , 2006aDietz et al., , 2006bDietz et al., 2013a,b), seals and narwhals (Monodon monoceros; Dietz et al., 2021;Houde et al., 2020), birds of prey (e.g. Dietz et al., 2006b;Ekblad et al., 2021;Sun et al., 2019), and Arctic foxes (Vulpes lagopus; e.g. ...
Mercury has become a ubiquitous hazardous element even ending up in pristine areas such as the Arctic, where it biomagnifies and leaves especially top predators vulnerable to potential health effects. Here we investigate total mercury (THg) concentrations and dietary proxies for trophic position and habitat foraging (δ¹⁵N and δ¹³C, respectively) in fur of 30 Arctic wolves collected during 1869–1998 in the Canadian High Arctic and Greenland. Fur THg concentration (mean ± SD) of 1.46 ± 1.39 μg g ⁻¹ dry weight is within the range of earlier reported values for other Arctic terrestrial species. Based on putative thresholds for Hg-mediated toxic health effects, the studied Arctic wolves have most likely not been at compromised health. Dietary proxies show high dietary plasticity among Arctic wolves deriving nutrition from both marine and terrestrial food sources at various trophic positions. Variability in THg concentrations seem to be related to the wolves' trophic positions rather than to different carbon sources or regional differences (East Greenland, the Foxe Basin and Baffin Bay area, respectively). Although the present study remains limited due to the scarce, yet unique historic study material and small sample size, it provides novel information on temporal and spatial variation in Hg pollution of remote Arctic species.
... d Combined means of early and late eggs from same clutch, 16 samples from each category Gabrielsen (2009) 1993 Svalbard, NOR b 0.39 ± 0.12 c , n = 5 Barrett et al. (1996) Svalbard, NOR 0.25 ± 0.11 c , n = 19 Hill (2018) greater than our study for eggs sampled at Tern Island, Canada (75° N) in 2008, but found eggs sampled farther south at East Bay (64° N) had approximately half as much mean THg ( Fig. 1; Table 1). While this is suggestive of an increasing latitudinal gradient for THg in eiders in the Canadian Arctic, as found in Arctic seabirds, both Mallory et al. (2004Mallory et al. ( , 2017 and Braune et al. (2005) found no such relationship in hepatic Hg analysis of Common Eiders. This difference in latitudinal patterns of Hg in seabirds and sea ducks may result from the benthic feeding behavior of sea ducks compared to the pelagic feeding of seabirds (Chen et al. 2014;Braune et al. 2015) which can correspond to lower trace contaminant levels in mollusk-based diets (Nielsen and Dietz 1989). ...
Mercury (Hg) levels in the environment have substantially increased over the past century leading to increased concentrations in many high trophic level predators, including Arctic seabirds. From the Canadian high Arctic, research on seabird eggs has documented some of the greatest concentrations of egg Hg anywhere in the Arctic. Farther east, in high Arctic Greenland, no similar data on Hg concentrations in eggs exist, making spatial comparisons unfeasible. To address this paucity of data, we collected whole eggs from Thick-billed Murre Uria lomvia (n = 11), Black-legged Kittiwake Rissa tridactyla (n = 9), and Common Eider Somateria mollissima (n = 12) in the high Arctic of northwest Greenland in the summer of 2014 and assessed their concentration of total Hg. Thick-billed Murre eggs had the highest mean total Hg concentrations (1.32 ± 0.42 mg g−1 dw) followed by kittiwakes (0.64 ± 0.19) and eiders (0.23 ± 0.10). When compared with murre and kittiwake egg samples collected in high Arctic Canada during the same time period, total Hg concentrations from northwest Greenland were higher, but not significantly. Based on what is known about lethal Hg concentrations in murre eggs, these results indicate that some murre eggs may be at risk for increased embryonic mortality and further monitoring is suggested to determine long-term trends in egg Hg concentrations.
... The broad-scale, inverse relationship between δ 13 C and latitude throughout the world's oceans results from temperature-induced variation in the concentration of CO 2 , which changes the extent to which phytoplankton incorporate 13 C during CO 2 uptake (Goericke and Fry 1994). A variety of other spatial patterns in δ 13 C, δ 15 N, and δ 34 S have been recognized in marine, freshwater, and terrestrial environments, and these isoscapes can and have been used for studies of movement patterns in a variety of birds (Kelly 2000, Rubenstein and Hobson 2004, Braune et al. 2005, Hebert and Wassanaar 2005, Coulton et al. 2010, Wiley et al. 2012. In some cases, samples from museum specimens have helped to describe isoscapes by increasing their spatial coverage and the rapidity of their development (e.g., Kelly et al. 2002). ...
Stable isotope analysis has expanded the usefulness of avian specimen collections in ways that were generally unanticipated by the original collectors. This technique enables aspects of avian ecology to be studied using very small samples of feather or other tissue taken from specimens. Stable isotope values can be informative about diet, trophic ecology, spatial habitat use, and the migratory connectivity of breeding and nonbreed-ing populations. They can also provide access to understudied time periods in a bird's annual cycle, particularly periods of molt. Use of museum specimens offers advantages for these studies: museum collections generally span longer time periods than field samples and represent broad geographic ranges. In this chapter, we review established and emerging isotopic techniques and their applications in avian ecology, with an aim to inspire and inform research using museum collections. We focus on analyses of bulk tissues and proteins, and we discuss ways in which sampling strategies for museum specimens can be adjusted to suit the research question, including considerations such as the timing of feather molt and the length of time during the life of a bird that is reflected by a sample. We also discuss general caveats for interpreting isotope data, the variance of which is usually influenced by multiple factors. In greater detail, we present recommendations for sampling museum specimens, such as avoiding a potential confounding influence of melanin concentration on carbon isotope values in feather, and minimizing damage to museum specimens when sampling. Stable isotope data from museum specimens have great potential to inform ornithologists about the trophic and spatial ecology of birds, and to provide long-term baseline data for studying how these attributes may be changing in the Anthropocene.
... d 13 C) and trace elements are also potentially useful for inclusion in probabilistic assignments or in restricting potential regions of origin. However, use of such data requires sufficient recapture data of banded birds to understand movement vectors or having baseline data on spatial structure of morphometrics or other elements [14,[35][36][37]. Pre-molt movements of Wilson's Warblers may skew results for some individuals particularly where there is the possibility of birds undertaking a latitudinal migration. ...
Stopovers used by birds during migration concentrate individuals from broad geographic areas potentially providing important information on catchment areas of birds moving through these sites. We combined stable isotope (δ ² H), genetic fingerprinting and band recovery data to delineate the molt origins of Wilson’s Warblers (Cardellina pusilla) migrating through a stopover site in southwestern Canada in the fall. We assessed changes in δ ² Hf indicating latitudinal origins with ordinal date to show this species likely underwent leapfrog migration through this site. Using the combined approach to determine origins, Wilson’s Warblers migrating through southwestern Alberta in 2015 were mostly from the western boreal population (n = 155, 96%) with some individuals from the Pacific Northwest (n = 1, 0.6%), Rocky Mountain (n = 2, 1.2%) and eastern boreal (n = 3, 1.8%) populations. Our results suggest that individuals migrating through our study site come from a broad catchment area potentially from a large part of northwestern North America. Future studies should link population changes at banding stations with other information to determine associations with large-scale landscape-level drivers (e.g. climate, land use).
... However, Mallory et al. (2004) found the opposite pattern for common eiders, with higher hepatic THg concentrations in eiders from Hudson Bay locations relative to birds sampled elsewhere throughout the Canadian Arctic. No spatial pattern was evident for hepatic concentrations of THg in long-tailed ducks (Clangula hyemalis) sampled from nine locations throughout the Canadian Arctic (Braune et al., 2005). Both eiders and long-tailed ducks are benthic feeders, however, and may be exposed to different Hg patterns via their prey than pelagic feeders (Chen et al., 2014) such as murres and other seabirds. ...
... However, Mallory et al. (2004) found the opposite pattern for common eiders, with higher hepatic THg concentrations in eiders from Hudson Bay locations relative to birds sampled elsewhere throughout the Canadian Arctic. No spatial pattern was evident for hepatic concentrations of THg in long-tailed ducks (Clangula hyemalis) sampled from nine locations throughout the Canadian Arctic (Braune et al., 2005). Both eiders and long-tailed ducks are benthic feeders, however, and may be exposed to different Hg patterns via their prey than pelagic feeders (Chen et al., 2014) such as murres and other seabirds. ...
... The Long-tailed Duck (Clangula hyemalis) is a circumpolar species of northern environments (Dement'ev and Gladkov 1952, Kistchinski 1973 and is listed as vulnerable on the IUCN Red List (BirdLife International 2012). The distribution of Longtailed Ducks appears to show a broad east-west divide in North America , without connectivity among breeding, molting, and wintering areas (Petersen et al. 2003;Braune et al. 2005; M. R. Petersen, unpubl. data). ...
Breeding, molting, fall and spring staging, and wintering habitats of the sea duck tribe Mergini are described based on geographic locations and distribution in North America, geomorphology, vegetation and soil types, and freshwater and marine characteristics. The dynamics of habitats are discussed in light of natural and anthropogenic events that shape areas important to sea ducks. Strategies for sea duck habitat management are outlined and recommendations for international collaboration to preserve key terrestrial and aquatic habitats are advanced.
... Piscivorous mergansers had higher muscle concentrations of THg up to 1.5 μg g −1 ww due to their higher trophic level (Braune and Malone, 2006b). Liver concentrations of THg in dabbling and diving duck species were also measured and were b 1.5 μg g −1 ww (Braune et al., 2005;Braune and Malone, 2006a). ...
The Canadian Arctic has vast freshwater resources, and fish are important in the diet of many Northerners. Mercury is a contaminant of concern because of its potential toxicity and elevated bioaccumulation in some fish populations. Over the last decade, significant advances have been made in characterizing the cycling and fate of mercury in these freshwater environments. Large amounts of new data on concentrations, speciation and fluxes of Hg are provided and summarized for water and sediment, which were virtually absent for the Canadian Arctic a decade ago. The biogeochemical processes that control the speciation of mercury remain poorly resolved, including the sites and controls of methylmercury production. Food web studies have examined the roles of Hg uptake, trophic transfer, and diet for Hg bioaccumulation in fish, and, in particular, advances have been made in identifying determinants of mercury levels in lake-dwelling and sea-run forms of Arctic char. In a comparison of common freshwater fish species that were sampled across the Canadian Arctic between 2002 and 2009, no geographic patterns or regional hotspots were evident. Over the last two to four decades, Hg concentrations have increased in some monitored populations of fish in the Mackenzie River Basin while other populations from the Yukon and Nunavut showed no change or a slight decline. The different Hg trends indicate that the drivers of temporal change may be regional or habitat-specific. The Canadian Arctic is undergoing profound environmental change, and preliminary evidence suggests that it may be impacting the cycling and bioaccumulation of mercury. Further research is needed to investigate climate change impacts on the Hg cycle as well as biogeochemical controls of methylmercury production and the processes leading to increasing Hg levels in some fish populations in the Canadian Arctic.
... However, Mallory et al. (2004) found the opposite pattern for common eiders, with higher hepatic THg concentrations in eiders from Hudson Bay locations relative to birds sampled elsewhere throughout the Canadian Arctic. No spatial pattern was evident for hepatic concentrations of THg in long-tailed ducks (Clangula hyemalis) sampled from nine locations throughout the Canadian Arctic (Braune et al., 2005). Both eiders and long-tailed ducks are benthic feeders, however, and may be exposed to different Hg patterns via their prey than pelagic feeders (Chen et al., 2014) such as murres and other seabirds. ...
This review summarizes data and information which have been generated on mercury (Hg) in the marine environment of the Canadian Arctic since the previous Canadian Arctic Contaminants Assessment Report (CACAR) was released in 2003. Much new information has been collected on Hg concentrations in marine water, snow and ice in the Canadian Arctic. The first measurements of methylation rates in Arctic seawater indicate that the water column is an important site for Hg methylation. Arctic marine waters were also found to be a substantial source of gaseous Hg to the atmosphere during the ice-free season. High Hg concentrations have been found in marine snow as a result of deposition following atmospheric mercury depletion events, although much of this Hg is photoreduced and re-emitted back to the atmosphere. The most extensive sampling of marine sediments in the Canadian Arctic was carried out in Hudson Bay where sediment total Hg (THg) concentrations were low compared with other marine regions in the circumpolar Arctic. Mass balance models have been developed to provide quantitative estimates of THg fluxes into and out of the Arctic Ocean and Hudson Bay. Several recent studies on Hg biomagnification have improved our understanding of trophic transfer of Hg through marine food webs. Over the past several decades, Hg concentrations have increased in some marine biota, while other populations showed no temporal change. Marine biota also exhibited considerable geographic variation in Hg concentrations with ringed seals, beluga and polar bears from the Beaufort Sea region having higher Hg concentrations compared with other parts of the Canadian Arctic. The drivers of these variable patterns of Hg bioaccumulation, both regionally and temporally, within the Canadian Arctic remain unclear. Further research is needed to identify the underlying processes including the interplay between biogeochemical and food web processes and climate change.
... This suggests a latitudinal gradient for Hg as previously observed for seabirds in the Canadian Arctic (Braune and Scheuhammer, 2008;Braune et al., 2002Braune et al., , 2006 as well as for Greenland species (Dietz et al., 1996). Akearok et al. (2010) also noted this latitudinal difference for common eiders (Somateria mollissima) in the Canadian Arctic, although Mallory et al. (2004a) found the opposite pattern for common eiders, and Braune et al. (2005a) found no spatial pattern for hepatic concentrations of Hg in long-tailed ducks (Clangula hyemalis) sampled throughout the Canadian Arctic. However, eiders and long-tailed ducks are primarily benthic feeders and therefore may be exposed to a different contaminant profile than birds such as murres and fulmars which feed primarily on pelagic species. ...
... Agencies in a number of countries systematically collect and archive bird eggs for toxicological and chemical analyses because eggs obtained early in the season can be re-laid, collection of 10-20 eggs has little impact on bird populations numbering in the thousands or millions, and the lipid-rich matrix accumulates many of the lipophilic toxins of interest [9,[15][16][17][18][19][20][21]. Archived egg specimen banks allow retrospective analysis of toxic contaminants. ...
Stable isotope ratios are biogeochemical tracers that can be used to determine the source of nutrients and contaminants in avian eggs. However, the interpretation of stable carbon ratios in lipid-rich eggs is complicated because (13)C is depleted in lipids. Variation in (13)C abundance can therefore be obscured by variation in percent lipids. Past attempts to establish an algebraic equation to correct carbon isotope ratios for lipid content in eggs have been unsuccessful, possibly because they relied partly on data from coastal or migratory species that may obtain egg lipids from different habitats than egg protein. We measured carbon, nitrogen and sulphur stable isotope ratios in 175 eggs from eight species of aquatic birds. Carbon, nitrogen and sulphur isotopes were enriched in lipid-extracted egg samples compared with non extracted egg samples. A logarithmic equation using the C∶N ratio and carbon isotope ratio from the non extracted egg tissue calculated 90% of the lipid-extracted carbon isotope ratios within ±0.5‰. Calculating separate equations for eggs laid by species in different habitats (pelagic, offshore and terrestrial-influenced) improved the fit. A logarithmic equation, rather than a linear equation as often used for muscle, was necessary to accurately correct for lipid content because the relatively high lipid content of eggs compared with muscle meant that a linear relationship did not accurately approximate the relationship between percent lipids and the C∶N ratio. Because lipid extraction alters sulphur and nitrogen isotope ratios (and cannot be corrected algebraically), we suggest that isotopic measurement on bulk tissue followed by algebraic lipid normalization of carbon stable isotope ratio is often a good solution for homogenated eggs, at least when it is not possible to complete separate chemical analyses for each isotope.
... μg g −1 dw; Pillatzki et al., 2011), mallards (Anas platyrhynchos; maximum~7.6 μg g −1 dw; Binkowski et al., 2012), white-winged scoters (Melanitta fusca; maximum 29.5 μg g −1 dw; Henny et al., 1995), and long-tailed ducks (Clangula hyemalis;~30 μg g − 1 dw; Braune et al., 2005, although one outlier from the western Arctic was~120 μg g − 1 dw). Cd in our eiders was Table 1 Arithmetic mean concentrations of Cd and Zn (μg·g −1 dw) in livers of female common eiders (Somateria ollissima) collected at their breeding colonies in 2008. ...
The common eider (Somateria mollissima) is an abundant sea duck breeding around the circumpolar Arctic, and is an important component of subsistence and sport harvest in some regions. We determined hepatic cadmium (Cd) and zinc (Zn) concentrations in the livers of breeding females sampled during three time periods including 1992/3, 2001/2 and 2008 at three sites spanning 53.7°N-75.8°N in the eastern Canadian Arctic. At all sites, concentrations of both Cd and Zn increased ~300% over this time period. The reasons for this rapid increase in concentrations are unclear.
... Stable isotope analyses of collagen have mainly been applied in archeological studies focusing on human and nonhuman faunal remains. Previous studies have applied collagen isotopic values to infer the diets, locations, and movements of living and extinct avian species (e.g., Hobson 1987;Hobson and Montevecchi 1991;Hobson 1993;Hobson et al. 1994;Braune et al. 2005). We used d 13 C in the collagen and muscles of migrating Garden Warblers to link habitat and diet use to condition and timing during migration. ...
In migratory birds, seasonal factors interacting at different stages of the annual cycle can influence individual life histories. These have been well documented for Nearctic-Neotropical birds. Yet, seasonal interactions between the wintering, migration, and breeding periods have not been demonstrated for Palearctic-African passerine migrants. We tested whether variation in long- and short-term dietary choice of the Garden Warbler Sylvia borin can influence events during the subsequent spring migration from the African winter quarters to the Palearctic breeding grounds. Using bone collagen and muscle carbon stable isotope (δ13C) analysis, we assessed the relationships between dietary history, body condition, and migration timing in the Garden Warbler during a return migration from Africa. We predicted that Garden Warblers arriving early will have significantly different muscle and collagen δ13C relative to those arriving later. Whereas muscle δ13C (referring to events in the immediate past) was not related to body condition, we found a strong association between body condition and collagen δ13C signatures (representing the integration of long-term events). Collagen and muscle δ13C indicate that birds passing through later originated from moister or cooler geographic areas. The observed variation in isotope signatures might relate to differences in habitat and geographic/population origin, or in dietary intake.
... Measurement of stable carbon (C) and nitrogen (N) isotope ratios of bone collagen allowed for appraisal of the long-term assimilation of food resources by these wolves. Bone collagen is remodeled at a rate such that isotope measurements are thought to reflect diets integrated over a period ranging from a few years (Gannes et al. 1998, Bocherens andDrucker 2007) to an individual's entire life (Braune et al. 2005). Because we knew the spatial distribution of home ranges of wolves we sampled, we could assess the contribution of salmon to wolf diets relative to the availability of salmon and ungulates across the Denali landscape. ...
... Stable-isotopic ratios of avian egg components can provide dietary information and permit inferences about contributions of endogenous and exogenous nutrient sources from differing habitats such as, marine or freshwater systems , Hobson et al.1997). Stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N) are typically enriched in marine versus freshwater systems and these isotopic signatures are incorporated by consumers (Braune et al. 2005). Stable-carbon and nitrogen isotopic analyses of avian eggs are particularly amenable because nutrients required for egg production are either derived from nutrient reserves or directly from the diet of laying females . ...
... In fact, almost any body tissue can yield information on diet, and muscle, liver, bone collagen and even breath have been utilized (Alisauskas & Hobson 1993, Hatch et al . 2002, Braune et al . 2005, Podelsak et al . 2005, Baduini et al . 2006). However, some of these require sacrifice of the animal, unless it has already died of other causes (e.g. hunting). ...
In the past 20 years the use of stable isotope analysis has become increasingly common in ecological studies. In fact, in some instances these techniques have yielded remarkable insights into the foraging preferences and migrations of birds. Despite these advances and the potential of the approach, it is possibly still not as widely used as might be expected. In this paper we aim to illustrate the potential of the approach in the hope of encouraging more avian ecologists to think again about how these techniques might provide insights in the systems on which they work. We discuss some of the principles behind the approach, and review some of the more recent ornithological studies that have used stable isotope techniques to trace trophic pathways or infer migratory origins. We follow this by discussing some of the latest ideas on how stable isotopes may be used to generate community metrics and close by detailing the important assumptions and caveats that should be considered before undertaking any studies using this technique.
... Red Knot Calidris canutus and Ruddy Turnstone Arenaria interpres) and waterfowl (e.g. Long-tailed Duck Clangula hyemalis), have d 13 C values with much wider ranges ()16.6 to )24.7&, )18.1 to )24.1&, )17 to )21&, respectively), mainly as a result of seasonal shifts in foraging between marine and terrestrial areas (Morrison & Hobson 2004, Braune et al. 2005. ...
Gyrfalcons Falco rusticolus use the same nest-sites over long periods of time, and in the cold dry climate of Greenland, guano and other nest debris decay slowly. Nineteen guano samples and three feathers were collected from 13 Gyrfalcon nests with stratified faecal accumulation in central-west and northwest Greenland. Samples were 14C dated, with the oldest guano sample dating to c. 2740–2360 calendar years (cal yr) before present (BP) and three others were probably > 1000 cal yr BP. Feather samples ranged from 670 to 60 cal yr BP. Although the estimated age of material was correlated with sample depth, both sample depth and guano thickness gave a much less reliable prediction of sample age than use of radiocarbon dating on which the margin of error was less. Older samples were obtained from sites farther from the current Greenland Ice Sheet and at higher elevations, while younger samples were closer to the current ice sheet and at lower elevations. Values for δ13C showed that Gyrfalcons nesting farther from the Greenland Ice Sheet had a more marine diet, whereas those nesting closer to the ice sheet (= further inland) fed on a more terrestrial diet. The duration of nest-site use by Gyrfalcons is a probable indicator of both the time at which colonization occurred and the palaeoenvironmental conditions and patterns of glacial retreat. Nowhere before has such extreme long-term to present use of raptor nest-sites been documented.
... Measurement of stable carbon (C) and nitrogen (N) isotope ratios of bone collagen allowed for appraisal of the long-term assimilation of food resources by these wolves. Bone collagen is remodeled at a rate such that isotope measurements are thought to reflect diets integrated over a period ranging from a few years (Gannes et al. 1998, Bocherens andDrucker 2007) to an individual's entire life (Braune et al. 2005). Because we knew the spatial distribution of home ranges of wolves we sampled, we could assess the contribution of salmon to wolf diets relative to the availability of salmon and ungulates across the Denali landscape. ...
Wolves (Canis lupus) in North America are considered obligate predators of ungulates with other food resources playing little role in wolf population dynamics or wolf prey relations. However, spawning Pacific salmon (Oncorhyncus spp.) are common throughout wolf range in northwestern North America and may provide a marine subsidy affecting inland wolf-ungulate food webs far from the coast. We conducted stable-isotope analyses for nitrogen and carbon to evaluate the contribution of salmon to diets of wolves in Denali National Park and Preserve, 1200 river-km from tidewater in interior Alaska, USA. We analyzed bone collagen from 73 wolves equipped with radio collars during 1986-2002 and evaluated estimates of salmon in their diets relative to the availability of salmon and ungulates within their home ranges. We compared wolf densities and ungulate:wolf ratios among regions with differing salmon and ungulate availability to assess subsidizing effects of salmon on these wolf-ungulate systems. Wolves in the northwestern flats of the study area had access to spawning salmon but low ungulate availability and consumed more salmon (17% +/- 7% [mean +/- SD]) than in upland regions, where ungulates were sixfold more abundant and wolves did or did not have salmon spawning areas within their home ranges (8% +/- 6% and 3% +/- 3%, respectively). Wolves were only 17% less abundant on the northwestern flats compared to the remainder of the study area, even though ungulate densities were 78% lower. We estimated that biomass from fall runs of chum (O. keta) and coho (O. kisutch) salmon on the northwestern flats was comparable to the ungulate biomass there, and the contribution of salmon to wolf diets was similar to estimates reported for coastal wolves in southeast Alaska. Given the ubiquitous consumption of salmon by wolves on the northwestern flats and the abundance of salmon there, we conclude that wolf numbers in this region were enhanced by the allochthonous subsidy provided by salmon and discuss implications for wolf-ungulate relations.
... Hg is a potentially toxic contaminant found in varying levels in Arctic marine biota (e.g., Rigét et al., 2007), and marine biota have been used to monitor the health of the marine environment ( Barrie et al., 1992;Furness and Camphuysen, 1997). In the Canadian Arctic, analyses of tissues from marine birds have revealed spatial differences in Hg concentrations within species ( Braune et al., 2002Braune et al., , 2005Mallory et al., 2004), as well as a temporal trend of increasing Hg in some areas since the 1970s (Braune, 2007). ...
Mercury (Hg) is a toxic metal that has been of increasing concern in the Canadian Arctic. We measured total Hg in eggs of three marine birds (Arctic terns Sterna paradisaea, common eiders Somateria mollissima borealis, long-tailed ducks Clangula hyemalis) that breed in the Canadian Arctic, to compare Hg laying order effects from the same clutch and to examine Hg among species. Early-laid eggs of all three species had 24-48% higher Hg concentrations than late laid eggs. Arctic terns had approximately twice the concentration of Hg in their eggs as the two duck species, and Hg in eider eggs from the High Arctic was higher than Hg in eggs from the Low Arctic. Higher Hg in tern eggs was consistent with this species occupying a higher trophic position in marine food webs, as indicated by stable nitrogen isotope (delta(15)N) values. The egg-laying sequence may need to be considered for Hg biomonitoring studies where small samples sizes are planned, and early eggs may be preferable for such studies since early eggs may be more representative of potential maximum levels of Hg in the marine food webs.
... It is likely that there is also variation in other elements such as S and Sr, which could also be reflected in spores or cells. Though no studies of isotope ratios of these elements in bacteriological media have been published, data for their variations in plant and animal materials suggest that microbiological media should vary as well (2,4,5,8,27,42). If that variation is translated into microbes, then incorporation of these elements into an isotopic signature would add to its discriminating power. ...
In the aftermath of the anthrax letters of 2001, researchers have been exploring various analytical signatures for the purpose
of characterizing the production environment of microorganisms. One such signature is stable isotope ratios, which in heterotrophs,
are a function of nutrient and water sources. Here we discuss the use of stable isotope ratios in microbial forensics, using
as a database the carbon, nitrogen, oxygen, and hydrogen stable isotope ratios of 247 separate cultures of Bacillus subtilis 6051 spores produced on a total of 32 different culture media. In the context of using stable isotope ratios as a signature
for sample matching, we present an analysis of variations between individual samples, between cultures produced in tandem,
and between cultures produced in the same medium but at different times. Additionally, we correlate the stable isotope ratios
of carbon, nitrogen, oxygen, and hydrogen for growth medium nutrients or water with those of spores and show examples of how
these relationships can be used to exclude nutrient or water samples as possible growth substrates for specific cultures.
Mercury (Hg) is a neurotoxin that can be particularly harmful to top predators because it biomagnifies through the food web. Due to variation in the food web structure, variation in Hg exposure in predators may represent variation in diet rather than Hg availability. We measured Hg in eggs from six seabird species (N = 537) over 47 years. In contrast to expectation, storm-petrels feeding partially on invertebrates had the highest Hg burden while herons feeding on large fish had the lowest Hg burden. A multiple regression showed that Hg correlated with δ34S (R2 = 0.86) rather than trophic level (δ15N of ‘trophic’ amino acids). Sulfate-rich environments (high δ34S) have sulfate-reducing bacteria that produce methylmercury. Variation in Hg within and among seabirds near the top of the food web was associated with variation in δ34S at the base of the food web more so than trophic position within the food web. Hg levels in seabirds only changed over time for those species where δ34S also varied in tandem; after accounting for diet (δ34S), there was no variation in Hg levels. Variation in Hg in seabirds across space and time were associated with the origin of sulfur in the diet.
This paper reviews factors affecting site selection amongst waterfowl (Anatidae)
during the flightless remigial moult, emphasising the roles of predation and food
supply (especially protein and energy). The current literature suggests survival during
flightless moult is at least as high as at other times of the annual cycle, but documented
cases of predation of flightless waterfowl under particular conditions lead us to infer
that habitat selection is generally highly effective in mitigating or avoiding predation.
High energetic costs of feather replacement and specific amino-acid requirements for
their construction imply adoption of special energetic and nutritional strategies at a
time when flightlessness limits movements. Some waterfowl meet their energy needs
from endogenous stores accumulated prior to remigial moult, others rely on
exogenous supply, but this varies with species, age, reproductive status and site.
Limited evidence suggests feather proteins are derived from endogenous and
exogenous sources which may affect site selection. Remigial moult does not occur
independently of other annual cycle events and is affected by reproductive investment
and success. Hence, moult strategies are affected by age, sex and reproductive history,
and may be influenced by the need to attain a certain internal state for the next stage
in the annual cycle (e.g. autumn migration). We know little about habitat selection
during moult and urge more research of this poorly known part of the annual cycle,
with particular emphasis on identifying key concentrations and habitats for specific
flyway populations and the effects of disturbance upon these. This knowledge will
better inform conservation actions and management actions concerning waterfowl
during moult and the habitats that they exploit.
The Canadian Arctic contains vast freshwater resources that cover about 140,000 km 2 of land north of 60° latitude (Prowse et al. 2009). Freshwater fish are important in the diet of many Northerners, particularly in the Northwest Territories, Yukon, and northern Quebec. Over the last two decades, extensive monitoring of Hg in freshwater fish has been conducted across the Canadian Arctic, and in some lakes, concentrations of Hg in top predator species exceed Health Canada's consumption guideline for commercial sale of fish. While trophic position, age, and size of fish have been identified as important factors, no geographic trends were discernable for the elevated Hg levels (Fisk et al. 2003). In the previous Canadian Arctic Contaminants Assessment Report (CACAR II), additional study was recommended to better explain the high lake-to-lake variability of Hg in freshwater fish and to investigate potential influences of atmospheric mercury depletion events (AMDEs) and climate change on food web bioaccumulation of Hg (Fisk et al. 2003). Several important advances have been made in our understanding of the Hg cycle in Arctic freshwater eco-systems during Phase III of the Northern Contaminants Program (NCP), particularly on Hg concentrations in water, Hg fluxes to sediment, methylmercury (MeHg) cycling, bioaccumulation in food webs, temporal changes in fish Hg levels, and impacts of climate change. Water concentrations of Hg are now available for Arctic lakes, ponds, and several large rivers. Mercury profiles in lake sediments across the Canadian Arctic provide new esti-mates of deposition rates to fresh waters. Production and loss rates of MeHg in ponds were modelled, and snowmelt fluxes of MeHg to lakes were investigated. To determine factors influencing lake-to-lake variability in Hg bioaccumulation, food webs were studied in Arctic lakes where landlocked char or trout are the top predator fish. A novel approach to tracing Hg sources using Hg stable isotopes was also applied to some of these Arctic lake food webs. Recent studies examined potential influences of climate change on Hg bioaccumulation in fish and on Hg sequestration in lake sediments. Impacts of thawing permafrost on Hg transport to lakes are under investigation in the Mackenzie River basin. Annual monitoring of key fish species during Phase III of the NCP has further strengthened the temporal trend datasets for the freshwater environment.
The isotopic distribution of the atoms composing the molecules of microorganisms is a function of the substrates used by the organisms. The stable isotope content of an organism is fixed so long as no further substrate consumption and biosynthesis occurs, while the radioactive isotopic content decays over time. The distribution of stable isotopes of C, N, O and H in heterotrophic microorganisms is a direct function of the culture medium, and therefore the stable isotope composition can be used to associate samples with potential culture media and also with one another. The 14C content depends upon the 14C content, and therefore the age, of the organic components of the culture medium, as well as on the age of the culture itself. Stable isotope signatures can thus be used for sample matching, to associate cultures with specific growth media, and to predict characteristics of growth media.
This paper presents design, fabrication, and testing of a microscale ceramic reactor for the pyrolysis of organic compounds. One application for this pyrolysis reactor is to convert the oxygen and hydrogen atoms in organic compounds to CO and H2 for isotope ratio measurements in a continuous flow mode. Existing commercial pyrolyzers use high carrier gas flow rates (typically 80−100 mL/min) such that >95% of the CO and H2 produced from a given sample is vented before introduction into the mass spectrometer. We describe here the fabrication and testing of a microscale pyrolysis reactor designed to be compatible with existing isotope ratio mass spectrometers. The microreactor uses carrier gas flow rates of 3−5 mL/min, decreasing the proportion of the CO and H2 lost in venting and permitting analysis of samples 20−50 times smaller than can be analyzed with conventional pyrolysis reactors. Results have shown that organic compounds, such as 1-butanol, ethanol, and ethanolamine, can be fully decomposed to desired products CO and H2, at a temperature of 1200 °C, which is 200 °C lower than conventionally reported. Furthermore, we are able to eliminate undesired products such as methane and CO2 in the pyrolysis process. The proof-of-concept experimental results clearly demonstrate that the micropyrolyzer quantitatively converts organic compounds to gases suitable for isotope ratio analysis.
The sex of a bird can, in principle, affect exposure and accumulation of mercury. One conventional explanation for sex differences in mercury burden suggests female birds should have lower concentrations than conspecific males, because breeding females can depurate methylmercury to their eggs. However, sex differences in body burden of mercury among birds are not consistent. We used meta-analysis to synthesize 123 male-female comparisons of mercury burden from 50 studies. For breeding birds, males had higher concentrations of mercury than did females, supporting egg depuration as a mechanism. However, the percentage of female body mass represented by a clutch did not significantly predict the magnitude of the sex difference in mercury contamination, as predicted. Furthermore, whether species were semialtrical or altrical versus semiprecocial or precocial also did not explain sex differences in mercury burden. Foraging guild of a species did explain near significant variation in sex differences in mercury burden where piscivores and invertivores showed significant sex differences, but sex differences were not detected for carnivores, herbivores, insectivores, and omnivores. The magnitude and direction of sexual size dimorphism did not explain variation in sex differences in mercury burden among breeding birds. We reveal targeted research directions on mechanisms for sex differences in mercury and confirm that sex is important to consider for environmental risk assessments based on breeding birds.
Arsenic is known to accumulate with iron plaque on macrophyte roots. Three to four years after the Aznalcóllar mine spill (Spain), residual arsenic contamination left in seasonal wetland habitats has been identified in this form by scanning electron microscopy. Total digestion has determined arsenic concentrations in thoroughly washed ‘root + plaque’ material in excess of 1000 mg kg−1, and further analysis using X-ray absorption spectroscopy suggests arsenic exists as both arsenate and arsenite. Certain herbivorous species feed on rhizomes and bulbs of macrophytes in a wide range of global environments, and the ecotoxicological impact of consuming arsenic rich iron plaque associated with such food items remains to be quantified. Here, greylag geese which feed on Scirpus maritimus rhizome and bulb material in areas affected by the Aznalcóllar spill are shown to have elevated levels of arsenic in their feces, which may originate from arsenic rich iron plaque.
Numbers of wintering sea ducks, including buffleheads (Bucephala albeola; BUFF), common goldeneyes (Bucephala clangula; COGO), and long-tailed ducks (Clangula hyemalis; LTDU), increased substantially at Lake Ontario after Dreissenid mussels (Dreissena bugensis and D. polymorpha) colonized the Great Lakes. Invertebrates, including Dreissenid mussels, are major diving duck prey items that can transfer some trace elements, such as selenium (Se) to higher trophic levels. Se can be problematic for waterfowl and it often has been detected at elevated levels in organisms using the Great Lakes. There are, however, few data on hepatic Se concentrations in sea ducks, particularly during the winter at Lake Ontario. In this study, we evaluated interspecific differences and temporal trends in hepatic Se concentrations among BUFF (n = 77), COGO (n = 77), and LTDU (n = 79) wintering at Lake Ontario. All three species accumulated Se throughout winter, but COGO did so at a higher rate than did BUFF and LTDU. Overall, Se concentrations were higher in LTDU [mean = 22.7; 95% CI = 20.8-24.8 microg/g dry weight (dw)] than in BUFF ([mean = 12.3; 95% CI = 11.6-13.1 microg/g dw) and COGO ([mean = 12.0; 95% CI = 10.7-3.5 microg/g dw) throughout the winter. Se concentrations were deemed elevated (>33 microg/g dw) in 0%, 5%, and 19% of BUFF, COGO, and LTDU, respectively. Presently there are no data on Se toxicity end points for these species, so it is unclear how acquiring concentrations of these magnitudes affect their short- and long-term health or reproduction.
El Hondo is a key area for marbled teal and white-headed duck. We present Pb, Cu, Zn, Se, and As data for bone and liver in birds found dead between 1996 and 2001. Several metals were higher in adult white-headed ducks than in marbled teal. They were higher in female than in male white-headed ducks, and did not differ with sex in marbled teal, but did by age. Lead in liver of adults was influenced by Pb shot ingestion, which was detected in 21% of marbled teal and in 71% of white-headed duck. No marbled teal had liver levels indicative of Pb poisoning, while 86% of white-headed ducks did. Selenium, Zn, and Cu were elevated in 13%, 7%, and 39% of birds, respectively. Whilst Pb shot poses the greatest threat to these species, further work should assess exposure via plants, invertebrates, water, and sediments for other metals, and investigate possible sub-lethal effects.
Total mercury and selenium were measured in livers of green-winged teal, northern pintails, buffleheads, king eiders, Barrow's and common goldeneyes, surf and white-winged scoters collected from 12 sites across northern Canada between 1988 and 1994. Hepatic mercury concentrations were <1.0 mg x kg(-1) ww in 80% of the birds analyzed. Mercury levels did not vary much among species, with green-winged teal, northern pintails, and white-winged scoters, in particular, generally having quite low levels (<0.5 mg x kg(-1) ww). Northern pintails had the lowest Se concentrations (<2.5 mg x kg(-1) ww) overall whereas the higher Se concentrations (10-20 mg x kg(-1) ww) were found in the king eiders and scoters. Selenium showed a much greater variation in concentrations, particularly in the king eiders and scoters. Hepatic mercury concentrations found in the waterfowl analyzed in this study were an order of magnitude lower than toxicological threshold levels found in the literature. However, hepatic selenium concentrations in 33% of the females exceeded 3.0 mg x kg(-1) ww and some king eiders as well as some surf and white-winged scoters contained hepatic selenium concentrations >10 mg x kg(-1) ww suggesting levels of potential concern.
The measurement of stable isotopes of nitrogen and carbon in tissues of marine consumers can provide trophic-level information that is a time-integrated approximation of assimilated diet. By measuring deltaN-15 and delta-C-13 concentrations in liver, muscle and bone collagen of 7 species of seabirds inhabiting the Barrow Strait - Lancaster Sound region, Northwest Territories, Canada, estimates of short-, intermediate-, and long-term trophic level (TL), respectively, were established. Trophic estimates were based on a simple model incorporating diet-tissue fractionation established through the captive rearing of piscivorous birds on known isotopic diets. DeltaC-13 was not a useful indicator of trophic position in this marine food web but may indicate inshore or benthic vs offshore or pelagic feeding preferences in seabirds. DeltaN-15 was a useful indicator and ranged from 12.7 +/- 0.3 parts per thousand (TL 3.3) in liver of dovekies Alle alle to 19.1 +/- 0.8 parts per thousand in the bone collagen of glaucous gulls Larus hyperboreus. Consistent with their known diets, dovekies and common eiders Somateria mollissima showed lowest trophic positions for all tissues; black-legged kittiwakes Rissa tridactyla, thick-billed murres Uria lomvia, northern fulmars Fulmarus glacialis and black guillemots Cepphus grylle showed intermediate trophic positions (TL 3.9 to 4.3) and glaucous gulls showed highest trophic position (TL 4.5 to 4.8). In general, seabirds increased their consumption of lower-trophic-level invertebrates during the breeding season over their lifetime averages but fed their chicks diets consisting of high proportions of fish. Isotopic estimates suggest greater dependence on lower-trophic-level prey by murres, fulmars, kittiwakes and guillemots than previously established through conventional dietary techniques.
We measured stable-carbon [C-13/C-12] and/or nitrogen [N-15/N-14] isotope ratios in 322 tissue samples [minus lipids] representing 43 species from primary producers through polar bears Ursus maritimus in the Barrow Strait-Lancaster Sound marine food web during July-August, 1988 to 1990. delta-C-13 ranged from -21.6 + 0.3 parts per thousand for particulate organic matter [POM] to -15.0 +/- 0.7 parts per thousand for the predatory amphipod Stegocephalus inflatus. Delta-N-15 was least enriched for POM [5.4 +/- 0.8 parts per thousand], most enriched for polar bears [21.1 +/- 0.6 parts per thousand], and showed a step-wise enrichment with trophic level of + 3.8 parts per thousand. We used this enrichment value to construct a simple isotopic food-web model to establish trophic relationships within this marine ecosystem. This model confirms a food web consisting primarily of 5 trophic levels. delta-C-13 showed no discernible pattern of enrichment after the first 2 trophic levels, an effect that could not be attributed to differential lipid concentrations in food-web components. Although Arctic cod Boreogadus saida is an important link between primary producers and higher trophic-level vertebrates during late summer, our isotopic model generally predicts closer links between lower trophic-level invertebrates and several species of seabirds and marine mammals than previously established.
Stable-carbon isotope analyses of bone collagen of gulls (Larus spp.) were used to estimate the relative proportion of marine and terrestrial protein in the diets of gulls that are known to use both types of food sources. Mean δ13C values for Glaucous-winged Gulls (n = 23) collected at a Vancouver dump and for Western Gulls (n = 18) from Southeast Farallon Island were −15.0 ± 1.3 and −15.1 ± 0.5‰, respectively. No significant difference in δ13C values was found between adult male and female Western Gulls. Archaeological gull bones (n = 3) show a mean δ13C value of −13.6 ± 1.0‰ and support the assumed marine end point of −13.0‰. The range of terrestrial protein in the diets of coastal gulls was 0–61%. The narrow distribution of δ13C values for Western Gulls from the Southeast Farallon Island colony suggests that gull colonies may be calibrated so that changes in dependence on terrestrial protein can be monitored.
Elevated dietary intake of selenium (Se) causes dramatic teratogenic and other reproductive effects in water birds at dietary levels only a few times greater than those that are generally regarded as nutritionally essential. Possible risks to the health of Canadian water birds and other wildlife from Se may be posed by seleniferous habitats in western Canadian provinces, and over-wintering by migratory water birds in some National Wildlife Refuges in the western U.S.A. where Se-related deaths and embryonic deformities in birds have occurred. These Refuges have in common an arid climate, closed drainage basins, seleniferous Cretaceous geology, and they receive irrigation drainage water from nearby agricultural areas. Similar conditions occur in SW Saskatchewan and SE Alberta, and these areas overlap parts of the critical water bird habitat of the region. Selenium concentrations in wetland ponds, agricultural tile drainage water and bird tissues in the western provinces are, with a few exceptions, generally lower than threshold concentrations for reproductive toxicity. However, some surface waters and aquifers contain dissolved Se concentrations that exceed guidelines for the protection of aquatic life, irrigation uses, and human and livestock drinking water. Use of this aquifer water for irrigation or replacement of freshwater flows into wetlands would greatly increase the risk of Se bioaccumulation to hazardous levels in water bird food chains.Key words: selenium, toxicity, birds, wildlife, Canada.
ABSTR^CT.--Stable-isotope analyses (carbon [13C/12C] and sulfur [ • 4S/32S]) were per-formed on eggs of two migratory fish-eating birds, Caspian Terns (Sterna caspia) and Double-crested Cormorants (Phalacrocorax auritus) collected from Lake Ontario, Canada, to examine the extent to which nutrient reserves acquired on marine wintering grounds are transferred to eggs laid on freshwater breeding grounds. In order to establish isotopic patterns typical of eggs of birds using marine and freshwater C-3 biomes, eggs of Herring Gulls (Larus ar-gentatus), a year-round resident on the Great Lakes, and those of Caspian Terns and Herring Gulls, breeding resepectively in the Gulf Coast of Texas and Atlantic Coast of Canada, were analyzed isotopically. Individual egg components showed distinct isotope values that were similar for both migratory and nonmigratory birds breeding in a freshwater biome and sig-nificantly lighter than those breeding in a marine biome. Hence, there appeared to be little evidence for significant nutrient transfer between the two biomes. The intermediate isotope values shown for egg components of Herring Gulls breeding on the Atlantic Coast suggest nutrient input from terrestrial as well as marine sources. Our results indicate the utility of stable-isotope analysis for tracing endogenous and exogenous contributions to reproduction in birds and further validate the use of migratory birds as indicators of breeding area con-taminant levels and their effects on the Great Lakes.
Stable isotopic ratios of animal tissues are related to those of their foods and can be used in palaeoecological reconstructions,
including those of extinct animals. Nitrogen isotopic analyses of marine organisms from coastal Newfoundland and Georges Bank
were used to construct a model predicting collagen δ15N values for seabirds feeding at various trophic levels (TL). This model was tested by measuring bone collagen δ15N values of extant alcids from the northwest Atlantic and high Arctic. Isotopic analysis of bone collagen of the extinct great
auk (Pinguinus impennis), the last flightless seabird in the northern hemisphere, indicate that this species occupied a trophic continuum from TL3
(crustacean diets) to TL5 (diets of piscivorous fish). We suggest that (a) great auk chicks and juveniles occupied lower trophic
levels and probably consumed euphausiids, and (b) great auks fed offspring via regurgitation, as do dovekies (Alle alle), the only extant fully planktivorous alcid in the Atlantic, and unrelated penguins of the southern hemisphere.
To understand the ecology of migratory animals it is important to link geographic regions used by individuals including breeding,
wintering, and intermediate stopover sites. Previous conventional approaches used to track animal movements have relied on
extrinsic markers and typically the subsequent recovery of individuals. This approach has generally been inappropriate for
most small, or non-game animals. The use of intrinsic markers such as fatty acid profiles, molecular DNA analyses, and the
measurement of naturally occurring stable isotopes in animal tissues offer alternative approaches. This paper reviews the
use of stable isotope analyses (primarily δ13C, δ15N, δ34S, δD, δ87Sr) to trace nutritional origin and migration in animals. This approach relies on the fact that foodweb isotopic signatures
are reflected in the tissues of organisms and that such signatures can vary spatially based on a variety of biogeochemical
processes. Organisms moving between isotopically distinct foodwebs can carry with them information on the location of previous
feeding. Such an approach has been used to track animal use of inshore versus offshore, marine versus freshwater, terrestrial
C3 versus marine, terrestrial mesic versus xeric, and C3 versus C4 or Crassulacean acid metabolism foodwebs. More recently, the use of stable hydrogen isotope analyses (δD) to link organisms
to broad geographic origin in North America is based on large-scale isotopic contours of growing-season average δD values
in precipitation. This technique, especially when combined with the assay of other stable isotopes, will be extremely useful
in helping to track migration and movement of a wide range of animals from insects to birds and mammals. Future research to
refine our understanding of natural and anthropogenic-induced isotopic gradients in nature, and to explore the use of stable
isotopes of other elements, is recommended.
Migration is the regular seasonal movement of animals from one place to another, often from a breeding site to a nonbreeding site and back. Because the act of migration makes it difficult to follow individuals and populations year round, our understanding of the ecology and evolution of migrating organisms, particularly birds, has been severely impeded. Exciting new advances in satellite telemetry, genetic analyses and stable isotope chemistry are now making it possible to determine the population and geographical origin of individual birds. Here, we review these new approaches and consider the relevance of understanding migratory connectivity to ecological, evolutionary and conservation issues.
Differential fractionation of stable isotopes of carbon during photosynthesis causes C-4 plants and C-3 plants to have distinct carbon-isotope signatures. In addition, marine C-3 plants have stable-isotope ratios of carbon that are intermediate between C-4 and terrestrial C-3 plants. The direct incorporation of the carbon-isotope ratio (C-13/C-12) of plants into consumers' tissues makes this ratio useful in studies of animal ecology. The heavy isotope of nitrogen (N-15) is preferentially incorporated into the tissues of the consumer from the diet, which results in a systematic enrichment in nitrogen-isotope ratio (N-15/N-14) with each trophic level. Consequently, stable isotopes of nitrogen have been used primarily to assess position in food chains. The literature pertaining to the use of stable isotopes of carbon and nitrogen in animal trophic ecology was reviewed. Data from 102 studies that reported stable-isotope ratios of carbon and (or) nitrogen of wild birds and (or) mammals were compiled and analyzed relative to diet, latitude, body size, and habitat moisture. These analyses supported the predicted relationships among trophic groups. Carbon-isotope ratios differed among species that relied on C-3, C-4, and marine food chains. Likewise, nitrogen-isotope ratios were enriched in terrestrial carnivorous mammals relative to terrestrial herbivorous mammals. Also, marine carnivores that ate vertebrates had nitrogen-isotope ratios that were enriched over the ratios of those that ate invertebrates. Data from the literature also indicated that (i) the carbon-isotope ratio of carnivore bone collagen was inversely related to latitude, which was likely the result of an inverse relationship between the proportion of carbon in the food chain that was fixed by C-4 plants and latitude; (ii) seabirds and marine mammals from northern oceans had higher nitrogen-isotope ratios than those from southern oceans; (iii) the nitrogen-isotope ratios of terrestrial mammals that used xeric habitats were higher than the ratios of those that used mesic habitats, indicating that water stress can have important effects on the nitrogen-isotope ratio; (iv) there was no relationship between body mass and nitrogen-isotope ratio for either bone collagen or muscle of carnivores; and (v) there was linear covariation between stable-isotope ratios of carbon and nitrogen in marine food chains (but not in terrestrial C-3 or C-4 food chains), which is likely a product of increases in carbon-isotope ratio with trophic level in marine food chains. Differences in stable-isotope composition among trophic groups were detected despite variation attributable to geographic location, climate, and analytical techniques, indicating that these effects are large and pervasive. Consequently, as knowledge of the distribution of stable isotopes of carbon and nitrogen increases, they will probably become an increasingly important tool in the study of avian and mammalian trophic ecology.
Because of the potential for increased trophic transfer of contaminants by zebra mussels (Dreissena sp.) to higher trophic levels, we collected four species of waterfowl (n = 65 ducks) from four locations in Lake Erie, Lake St. Clair, and Lake Michigan, USA, between 1991 and 1993 for organochlorine contaminant and trace element analyses. Geometric mean concentrations of total polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyldichloroethylene (DDE) were 1.35 and 0.15 mug/g wet weight in lesser scaup (Aythya affinis) carcasses and were below known effect levels. Total PCBs in 80% of carcasses, however, were above the U.S. Food and Drug Administration's threshold of 3.0 mug/g lipid weight for consumption of poultry. With the exception of selenium; trace elements were also at background or no-effect levels. Selenium concentrations in livers of 95% of lesser scaup, 90% of bufflehead (Bucephala albeola), and 72% of common goldeneye (Bucephala clangula) were in the elevated (>10 mug/g dry wt) or potentially harmful range (>33 mug/g dry wt). The effects of these high,selenium concentrations are unknown but should be investigated further based on reproductive effects observed in field and laboratory studies of dabbling ducks and because lesser scaup populations are declining. Concentrations of total PCBs in dreissenid mussels in western Lake Erie were 10 times higher than in the upper Mississippi River but were similar to concentrations in other industrialized rivers in Europe and the United States. Metal concentrations were similar to other industrialized sites where zebra mussels have been sampled.
Total mercury was determined in 99 oldsquaw (Clangula hyemalis) livers and 11 composite clutches collected on Lake Michigan and in northwest Hudson Bay. Residue levels were similar in different sex and age-classes collected during the same time period on Lake Michigan. Mercury levels were higher in oldsquaws collected in Hudson Bay than in those taken on Lake Michigan. Residues in the hen and clutch were positively correlated. Mercury in duckling livers was negatively correlated with the weight of the liver.
Use of habitat, food preferences, and food availability were studied for seven species of waterfowl (white-winged scoter (Melanitta deglandi), surf scoter (M. perspicillata), common scoter (Oidemia nigra), oldsquaw (Clangula hyemalis), common goldeneye (Bucephala clangula), bufflehead (B. albeola), and red-breasted merganser (Mergus serrator)) on a 34-km section of the New England coastline during 1968-70. The three scoters selectively used areas of sandy substrate and had very similar food habits. The principal foods were the Atlantic razor clam (Siliqua costata) and Arctic wedge clam (Mesodesma arctatum), which were characteristic of, and abundant in, sandy substrate. In contrast to scoters, goldeneye preferred areas of rocky substrate associated with rocky headlands. They fed primarily on amphipods, isopods, crabs, and gastropods, which were commonly found in the Irish moss (Chondrus crispus) covering of the rocky sublittoral areas. Red-breasted mergansers, like goldeneye, also used the rocky areas. They fed primarily on several small fish species that were observed among the Irish moss and crevices of the rocky substrate. Bufflehead had the most restrictive distribution, being confined mostly to estuaries. Bufflehead fed primarily on sand shrimp, which were found only in harbors with soft ooze bottoms. Oldsquaw had the most generalized diet of all the sea ducks. The major food items consisted of bivalves, gastropods, sand shrimp, and isopods, which were found throughout the study area and accounted for the generalized distribution of oldsquaw along the coastline and in the harbors. Sea ducks were concentrated near the mouths of the estuaries, where more abundant food resources particularly bivalves, were found. Although the species vary, the types of foods eaten by sea ducks were similar to those described in other studies. Thus, food availability, coupled with the physical structure of the substratum in the different coastal habitats, is apparently a major determinant in the way that coastal waterfowl selectively use habitat types. The described patterns of habitat usage appear to have implications for other wide geographical areas.
Stable carbon and nitrogen isotopic analyses were performed on tissues of 21 Marbled Murrelets (Brachyramphus marmoratus) collected in Barkley Sound (n = 18) and on Johnston Lake, British Columbia (n = 3). Three adult males had significantly lower muscle tissue δ 13C values (x̄ ± SD: -23 ± 2.7‰, n = 3) than did all other murrelets (- 16.5 ± 0.6‰, n = 18). Based on a model predicting muscle δ 13C values for murrelets feeding on freshwater and marine prey these three individuals had short-term freshwater-derived protein inputs to their diets ranging from 50 to 100%. The mean δ 13C value for Marbled Murrelet bone collagen (- 16.8 ± 0.3‰, n = 4) was not significantly different from that found for Ancient Murrelets (Synthliboramphus antiquus) from Reef Island, Queen Charlotte Islands. This suggests that while some Marbled Murrelets may feed exclusively on freshwater prey for a short but important period of several weeks, freshwater protein is not a significant long-term dietary component in their diets. Marbled Murrelets had a mean muscle δ 15N value of 15.3 ± 0.7‰ (n = 21). Because δ 15N values for freshwater and marine prey species overlapped significantly, stable-nitrogen isotope analysis did not distinguish between Marbled Murrelets feeding on freshwater or marine prey. The stable-nitrogen isotope values of muscle tissue from Marbled Murrelets were compared with those of nine other species of alcids from British Columbia and the high Arctic. The comparison indicates that stable-nitrogen isotope analysis is potentially useful for establishing trophic relationships in seabird communities.
Effective management of Canada geese (Branta canadensis) requires a reliable method to determine the population affiliation of geese in the harvest. We determined if stable isotope analysis of feather tissue could distinguish between migrant and resident populations. We obtained feather samples of migrants from Atlantic population of Canada geese in northern Quebec near Ungava Bay, Canada. We grouped resident population Canada geese as coastal residents and inland residents according to the habitats where they were captured in New Jersey. We analyzed for isotopes of carbon (δ 13C), nitrogen (δ 15N), and sulfur (δ 34S). We found significant differences among migrants, coastal residents, and inland resident for all 3 isotopes. Combinations of isotopic ratios for the 3 elements resulted in unique patterns among groups of geese. We entered the isotopic ratios into a discriminant analysis using collection site as the grouping variable (migrants, inland residents, and coastal residents). We formed 2 significant functions that discriminated among the 3 groups 92% of the time. The first function accounted for most of the variance, and was highly influenced by the isotope ratios for carbon and sulfur. The results indicate that stable isotope analysis of primary feathers can provide a reliable means to discriminate between migratory and resident populations of Canada geese. Stable isotope analysis is a promising technique for identifying the breeding areas of Canada geese, but additional studies are needed to determine inherent variability over broad geographic areas.
Zooplankton from the Bering, Chukchi, and Beaufort seas and a transect across the Arctic Ocean were collected from 369 stations on 18 cruises in the years 1985-1990 and 1993-1995. Carbon and nitrogen isotope ratio analyses were performed on the major taxonomic groups present-calanoid copepods, euphausiids and chaetognaths. The sampled waters around Alaska were divided into 11 subregions based on water mass characteristics and the zooplankton statistically tested for significant differences in the isotope ratios. Within all regions, copepods were significantly more depleted in C-13 than euphausiids (average delta(13)C difference for copepods = -1.1 parts per thousand than euphausiids), but showed no significant differences from euphausiids in delta(15)N except in the eastern Alaskan Beaufort Sea where copepods were relatively enriched in N-15. Th, greatest variability in isotope ratios was among geographic regions. All taxa tested were C-13-depleted in the eastern Beaufort Sea, the Arctic Ocean and in deep waters of the southwestern Bering Sea relative to the continental shelf waters of the Bering and Chukchi seas. The maximum enrichments were found in the southwestern Chukchi Sea and central Bering Sea shelf waters. The advection of water northward through the Bering Strait was evident as a plume of enriched zooplankton extending to the shelf break in the Arctic Ocean. In contrast, the delta(15)N within taxa generally increased moving northward from the deep Bering Sea to the Chukchi Sea and eastward into the Beaufort Sea. The delta(15)N values for chaetognaths were 2.5 to 3 parts per thousand more enriched than copepods or euphausiids in all locations, consistent nrith their carnivorous diet. Comparisons of zooplankton isotope ratios among years and cruises within the same region revealed no significant differences. Low delta(15)N and delta(13)C values in zooplankton of the pelagic Bering Sea are presumed to result from the isotopic discrimination arising in the presence of high nutrient abundances and slow phytoplankton growth rates whereas depleted values in coastal waters of the Canadian Beaufort Sea presumably derive from Mackenzie River inputs of terrestrially derived carbon and nitrogenous nutrients with low N-15 and C-13 abundances. The geographic heterogeneity in isotope ratios over short distances indicates a need for caution in the interpretation of isotope ratios in marine mammals and birds with regard to trophic status and habitat usage.
During a research cruise in 1979 to the area between New Guinea and northern Australia, 250 samples were collected for measurement of 13C/12C (δ13C) to analyse carbon flow in tropical marine food webs. Plants at the base of food webs could be divided into two groups on the basis of their mean δ13C values: benthic seagrasses (-8.8‰), macroalgae (-12.5‰) and epiphytic algae (-13.3‰) were enriched in 13C (had less-negative δ13C values) when compared to planktonic samples (-21.8‰). Animals collected offshore were enriched in 13C by up to 9.1‰ relative to planktonic samples and seemed to show an increasing 13C enrichment with increasing trophic level. Relative to these offshore specimens, animals collected in intertidal seagrass meadows were usually enriched in 13C by 2-8‰, indicating that 13C-enriched benthic plants are important food sources in grassflats. Unusual 13C- enriched values of -3 to -7‰ among benthic chitons, gastropods and holothurians at one grassbed site suggest that unsampled benthic microalgae are also important sources of food-web carbon in the Torres Strait.
Polychlorinated dibenzo-para-dioxins (PCDDs) are present as trace impurities in various manufactured chemicals and in combustion products. The chemical and environmental stability of PCDDs and their tendency to accumulate in fatty tissues have resulted in their widespread detection throughout the global ecosystem. The most toxic and extensively studied PCDD isomer is 2,3,7,8-tetrachlorodibenzo-para-dioxin (2,3,7,8-TCDD). Accidental contamination of the environment by 2,3,7,8-TCDD has resulted in deaths in many species of birds, wildlife, and domestic animals, and in the closing of rivers to fishing due to high residues in fish, i.e., >50 parts per trillion (ppt) wet weight. Laboratory studies with birds, mammals, aquatic organisms, and other species have conclusively demonstrated that exposure to 2,3,7,8-TCDD can be associated with acute and delayed mortality, carcinogenic, teratogenic, reproductive, mutagenic, histopathologic, and immunotoxic effects.
Stable isotope ratios provide clues about the origins and transformations of organic matter. A few key reactions control the isotopic composition of most organic matter. Isotopic variations introduced by these reactions are often passed on with little change so that isotopic measurements can indicate natural pathways and flows “downstream” from these key reactions. When chemical and metabolic processes scramble the information content of molecules, isotopic compositions are often preserved. This realization has prompted increasing use of stable isotope analyses as a tool for understanding complex ecological processes.
The Great Lakes Herring Gull Monitoring Program has annually provided information concerning levels of environmental contaminants in herring gull eggs since 1974, making it one of the longest running biomonitoring programs in the world. The program was initiated in response to observations of poor reproductive success in colonial waterbirds on the Great Lakes. Initial studies examined the role of halogenated hydrocarbons (HAHs) in causing this reproductive dysfunction. By the late 1970s, reproductive success in herring gulls had improved greatly and emphasis was placed on developing more sensitive indicators to measure the subtle effects associated with HAH exposure. Geographic and temporal trends in Great Lakes contamination were also elucidated. Analysis of herring gull tissues led to the identification of HAHs (mirex, photomirex, polynuclear aromatic hydrocarbons, chlorobenzenes, dioxins) previously undetected in Great Lakes upper trophic level biota. Data collected as part of this program have improved our understanding of contaminant sources and fate in the Great Lakes and have provided us with a means to assess our progress in controlling contaminant inputs. The extensive nature of this dataset has allowed detailed examination of the factors that regulate contaminant levels in this species. Most monitoring programs rely on less extensive datasets for the interpretation of environmental trends and may benefit from the mechanisms identified here. Research has also identified other stressors, e.g., dietary deficiencies, that may affect the success of Great Lakes herring gull populations. Ongoing monitoring of this species will continue to provide new insights into the dynamic Great Lakes ecosystem.Key words: herring gull, Larus argentatus, Great Lakes, environmental monitoring, halogenated hydrocarbons, contaminants.
Selective review and synthesis of the technical literature on copper and copper salts in the environment and their effects primarily on fishes, birds, mammals, terrestrial and aquatic invertebrates, and other natural resources. The subtopics include copper sources and uses; chemical and biochemical properties; concentrations of copper in field collections of abiotic materials and living organisms; effects of copper deficiency; lethal and sublethal effects on terrestrial plants and invertebrates, aquzatic organisms, birds, and mammals, including effects on survival, growth, reproduction, behavior, metabolism, carcinogenicity, mutagenicity, and teratogenicity; proposed criteria for the protection of human health and sensitive natural resources; and recommendations for additional research.
Ecological and toxicological aspects of silver (Ag) and silver salts in the environment are briefly summarized with an emphasis on natural resources. Elevated silver concentrations in biota occur in the vicinities of sewage outfalls, electroplating plants, mine waste sites, and silver-iodide seeded areas; in the United States, the photography industry is the major source of anthropogenic silver discharges into the biosphere. Silver and its compounds are not known to be mutagenic, teratogenic, or carcinogenic. Under normal routes of exposure, silver does not pose serious environmental health problems to humans at less than 50 ug total Ag/L drinking water or 10 ug total Ag/m3 air. Free silver ion, however, was lethal to representative species of sensitive aquatic plants, invertebrates, and teleosts at nominal water concentrations of 1.2 to 4.9 ug/L; sublethal effects were significant between 0.17 and 0.6 ug/L. Silver was harmful to poultry at concentrations as low as 1.8 mg total Ag/kg whole egg fresh weight by way of injection, 100 mg total Ag/L in drinking water, or 200 mg total Ag/kg in diets; sensitive mammals were adversely affected at total silver concentrations as low as 250 ug/L in drinking water, 6 mg/kg in diets, or 13.9 mg/kg whole body.
This account is a selective review and synthesis of the technical literature on nickel and nickel salts in the environment and their effects on terrestrial plants and invertebrates, aquatic plants and animals, avian and mammalian wildlife, and other natural resources. The subtopics include nickel sources and uses; physical, chemical, and metabolic properties of nickel; nickel concentrations in field collections of abiotic materials and living organisms; nickel deficiency effects; lethal and sublethal effects, including effects on survival, growth, reproduction, metabolism, mutagenicity, teratogenicity, and carcinogenicity; currently proposed nickel criteria for the protection of human health and sensitive natural resources; and recommendations for additional research.
Ecological and toxicological aspects of molybdenum (Mo) in the environment are briefly reviewed, with emphasis on fish and wildlife. Subtopics include sources and uses, chemical properties, mode of action, background concentrations in biological and nonbiological samples, and lethal and sublethal effects on terrestrial plants and invertebrates, aquatic organisms, birds, and mammals. Current recommendations for Mo and the protection of sensitive living resources are presented.
1. The numbers of cormorants Phalacrocorax carbo feeding at English freshwater fisheries during winter have increased rapidly over the last 20 years, causing concern among fishery managers and anglers.
2. In order to assess the extent of freshwater feeding, stable isotope ratios of carbon and nitrogen (δ13C and δ15N) in feathers of wild cormorants from inland freshwater fisheries were compared with those in the feathers of piscivorous birds with marine diets (captive ‘marine-fed’ cormorants, free-ranging shags Phalacrocorax aristotelis) and freshwater diets (juvenile goosanders Mergus merganser).
3. Isotope signatures of feathers represent the diet at the time of growth. Feathers grown at different times of the year were taken from wild cormorants; each feather type therefore represented the diet over a different temporal scale.
4. Isotopic analyses of feathers indicated that, when shot, nearly all of the cormorants had been feeding entirely on freshwater prey. The mean δ13C value of primary feathers growing when birds were shot was –22·2‰, indicative of an entirely freshwater diet.
5. The move to freshwater habitats from coastal breeding grounds occurred over several months, but once established cormorants appear to have fed at freshwater sites throughout the autumn and winter.
6. The suitability of using a two-source isotopic mixing model in order to quantify the extent of freshwater feeding in piscivorous birds is discussed.
7. Although the results indicate long-term residency and feeding in freshwater systems, they do not indicate whether birds were feeding regularly at the sites at which they were shot, or the composition of the diet. It is recommended that further studies using telemetry and multiple isotope analyses be carried out in order to address these issues.
Because of the potential for increased trophic transfer of contaminants by zebra mussels (Dreissena sp.) to higher trophic levels, we collected four species of waterfowl (n = 65 ducks) from four locations in Lake Erie, Lake St. Clair, and Lake Michigan, USA, between 1991 and 1993 for organochlorine contaminant and trace element analyses. Geometric mean concentrations of total polychlorinated biphenyls (PCBs) and p, p′-dichlorodiphenyldichloroethylene (DDE) were 1.35 and 0.15 μg/g wet weight in lesser scaup (Aythya affinis) carcasses and were below known effect levels. Total PCBs in 80% of carcasses, however, were above the U.S. Food and Drug Administration's threshold of 3.0 μg/g lipid weight for consumption of poultry. With the exception of selenium, trace elements were also at background or no-effect levels. Selenium concentrations in livers of 95% of lesser scaup, 90% of bufflehead (Bucephala albeola), and 72% of common goldeneye (Bucephala clangula) were in the elevated (>10 μg/g dry wt) or potentially harmful range (>33 μg/g dry wt). The effects of these high selenium concentrations are unknown but should be investigated further based on reproductive effects observed in field and laboratory studies of dabbling ducks and because lesser scaup populations are declining. Concentrations of total PCBs in dreissenid mussels in western Lake Erie were 10 times higher than in the upper Mississippi River but were similar to concentrations in other industrialized rivers in Europe and the United States. Metal concentrations were similar to other industrialized sites where zebra mussels have been sampled.
We examined the diet of Long-tailed Ducks (Clangula hyemalis) in the autumn and winter of 1998-99 in the Belcher Islands, Nunavut, Canada. Collections were made in early November before spa ice had formed and in February andMarch, the time of maximum ice cover. Eight birds collected in the autumn and 19 collected in the winter had food items in the proventriculus/esophagus. For birds collected in the fall, 89% (aggregate wet mass) of the diet consisted of the amphipod Calliopius laeviusculus. The remainder consisted of other smaller amphipods (5%) and sandlance (sandeels, Ammodytes sp.; 6%). In winter Long-tailed Duck diet consisted of the amphipod Is-chyrocerus anquipes (69%), fish eggs (probably sandlance; 24%), sandlance (1%) and otheramphipods (5%). Long-tailed Duck foraging at tile landfast ice flee edge along coasts fed mostly on fish and fish eggs, while those in polynyas amongislands fed on amphipods. Consuming soft-bodied prey with high energy densities is likely to allow Long-tailed Ducks to successfully winter in the predominately ice-covered Hudson Bay.
Forty out of 41 oldsquaw carcasses collected during a 3 month avian cholera outbreak in Chesapeake Bay, USA, in 1994 were culture positive for Pasteurella multocida. Pasteurella-positive birds collected in February had greater (p 0.05) mean (geometric) liver concentrations of cadmium (7.35 versus 3.71 g per g dry weight) and lower concentrations of selenium (9.90 versus 12.5 g per g dry weight) than Pasteurella-positive birds collected during March and April. The mercury content of the livers and cadmium content of the kidneys did not differ (p> 0.05) between birds collected early in the die-off and those collected in March and April. The liver and kidney concentrations of metals in the Pasteurella-positive birds collected in 1994 were compared to apparently healthy oldsquaw (n = 67) collected from Chesapeake Bay during 1985--1987, because healthy oldsquaw were not collected during the avian cholera outbreak in 1994. Compared to the apparently healthy oldsquaw collected in 1985--1987, the mean concentrations of cadmium (liver 4.32 versus 2.65 g per g dry weight and kidney 22.7 versus 11.5 g per g dry weight) were greater (p 0.05) in the oldsquaw which succumbed to avian cholera in 1994. In contrast, the liver concentrations of selenium (11.9 versus 17.8 g per g dry weight) and mercury (0.389 versus 1.83 g per g dry weight) were lower (p 0.05) in the birds from the 1994 die-off than for the apparently healthy oldsquaw collected in 1985--1987. Three birds from the 1985--1987 cohort and none of the birds from the 1994 cohort had liver lead concentrations greater than 4 g per g dry weight. The results of this study indicate a possible link between high cadmium tissue concentrations and susceptibility to avian cholera in oldsquaw
Arsenic (As) and selenium (Se) occur together in high concentrations in the environment and can accumulate in aquatic plants and invertebrates consumed by waterfowl. Ninety-nine pairs of breeding mallards (Anas platyrhynchos) were fed diets supplemented with As (sodium arsenate) at 0, 25, 100, or 400 g/g, in combination with Se (seleno-DL-methionine) at 0 or 10 g/g, in a replicated factorial experiment. Ducklings produced were placed on the same treatment combination as their parents. Arsenic accumulated in adult liver and egg, reduced adult weight gain and liver weight, delayed the onset of egg laying, decreased whole egg weight, and caused eggshell thinning. Arsenic did not affect hatching success and was not teratogenic. In ducklings, As accumulated in the liver and reduced body weight, growth, and liver weight. Arsenic did not increase duckling mortality, but it did decrease overall duckling production. Selenium accumulated in adult liver and egg, was teratogenic, and decreased hatching success. Selenium did not affect adult weight, liver weight, survival, onset of egg laying, egg fertility, egg weight, or eggshell thickness. In ducklings, Se accumulated in the liver and reduced body weight and growth, and increased liver weight. Selenium increased duckling mortality and decreased overall duckling production. Antagonistic interactions between As and Se occurred whereby As reduced Se accumulation in liver and egg, and alleviated the effects of Se on hatching success and embryo deformities. It was demonstrated that As and Se, in the chemical forms and at the dietary levels administered in this study, can adversely affect mallard reproduction and duckling growth and survival, and that As can alleviate toxic effects of Se.
Liver, muscle, kidney, and feather samples from nine species of seabirds were analyzed for total and organic (methyl) mercury (MM). Total mercury (TM) levels in liver showed great intra- and inter-species variations, with the concentrations varied from 306 g/g (dry weight) in black-footed albatross (Diomedea nigripes) to 4.9 g/g in arctic tern (Sterna paradisaea), while MM levels were less relatively variable. The order of MM concentrations in tissues of all the seabirds except oldsquaw (Clangula hyemalis) was as follows: liver > kidney > muscle. The mean percentage of MM in total was 35%, 36%, and 66% in liver, kidney, and muscle, respectively, for all the species. Statistically significant negative correlations were found between the proportion of MM to TM and concentrations of TM in the liver and muscle of black-footed albatross and in the liver of laysan albatross. Furthermore, the percentage of MM decreased with an increase in TM concentrations in the liver, muscle, and kidney of all the species. Black-footed albatross had the highest concentration and burden of mercury in the liver, wherein more than 70% of the TM occurred as inorganic mercury. On the other hand, the mercury burdens in feathers were less than 10% of the body burdens, indicating that excretion of mercury by moulting is negligible. The results suggest that some seabirds are capable of demethylating MM in the tissues (mainly in liver), and store mercury as an immobilizable inorganic form in the liver. It is noteworthy that the species with a high degree of demethylation capacity and slow moulting pattern showed low mercury burdens in feathers.
The stable nitrogen and carbon isotope ratios of bone collagen prepared from more than 100 animals representing 66 species of birds, fish, and mammals are presented. The δ15N values of bone collagen from animals that fed exclusively in the marine environment are, on average, 9%. more positive than those from animals that fed exclusively in the terrestrial environment; ranges for the two groups overlap by less than 1%. Bone collagen δ15N values also serve to separate marine fish from the small number of freshwater fish we analyzed. The bone collagen δ15N values of birds and fish that spent part of their life cycles feeding in the marine environment and part in the freshwater environment are intermediate between those of animals that fed exclusively in one or the other system. Further, animals that fed at successive trophic levels in the marine and terrestrial environment are separated, on average, by a 3%. difference in the δ15N values of their bone collagen. Specifically, carnivorous and herbivorous terrestrial animals have mean δ15N values for bone collagen of + 8.0 and + 5.3%., respectively. Among marine animals, those that fed on fish have a mean δ15N value for bone collagen of + 16.5%., whereas those that fed on invertebrates have a mean δ15N value of + 13.3%. These results support previous suggestions of a 3%. enrichment in δ15N values at each successively higher trophic level. In contrast to the results for δ15N values, the ranges of bone collagen δ13C values from marine and terrestrial feeders overlap to a great extent. Additionally, bone collagen δ13C values do not reflect the trophic levels at which the animals fed. These results indicate that bone collagen δ15N values will be useful in determining relative dependence on marine and terrestrial food sources and in investigating trophic level relationships among different animal species within an ecosystem. This approach should be applicable to animals represented by prehistoric or fossilized bone in which collagen is preserved.
Here, we report the results of a study to determine the frequency of elevated Pb concentrations in pectoral muscle tissue of hunter-killed game birds (mostly waterfowl), and to address the cause of occasionally observed high Pb values. Of 827 right pectoral muscle pools (1–12 individuals per pool), 92 had Pb concentrations greater than 0.5 μg/g wet weight, (∼2 μg/g dry weight). The average Pb concentration for these 92 pools was 12±38 μg/g wet weight (∼40±125 μg/g dry wt). When tissue from individuals making up some of these `high Pb' pools were analysed, 40 of 190 individual birds had Pb concentrations >5 μg/g dry weight in their right pectoral muscles. All tissue samples were examined visually prior to analysis, and none contained detectable Pb pellets. The average concentration of Pb in right pectoral muscle tissue of individual birds from high Pb pools with elevated muscle-Pb concentrations was 211±634 μg/g (n=40) and ranged from 5.5 to 3910 μg/g (dry wt). Large differences in Pb concentrations between right and left pectoral muscle of the same individuals, were often noted. The magnitude of the differences in Pb concentrations between left and right pectoral muscles of the same individual, and also between different samples taken from the same tissue, preclude both analytical error and biologically incorporated Pb as the cause of the elevated Pb concentrations in these animals. Radiography confirmed the presence of numerous small (<1 mm diameter) metallic fragments in pectoral muscle samples from these birds. Embedded fragments of metallic Pb from shot disintegration are a potential source of dietary Pb exposure for predators, and for human consumers of wild game, especially in communities that rely on subsistence hunting and for whom hunter-killed wild game represents a major food source. This risk can be eliminated by the use of non-toxic shot for hunting.
Concentrations of cadmium, lead, copper and zinc were measured in 774 livers, 266 kidneys and 271 ulnar bones from 15 species of ducks obtained from the Chesapeake Bay region. A major purpose of this study was to elucidate relationships between food habits and tissue accumulations of heavy metals in Chesapeake Bay waterfowl. Liver and kidney concentrations of cadmium were highest among two carnivorous seaduck species, Clangula hyemalis and Melanitta deglandi. In contrast, lead concentrations in tissues were generally highest in largely herbivorous species, such as Anas platyrhynchos, Anas rubripes and Anas strepera. Spent shot may be an important source for tissue burdens of lead in these ducks. No marked trends were observed between food habits and tissue concentrations of the nutrient elements, copper and zinc.
Explains isotope terminology and fractionation, and summarises isotopic distributions in the C, N and S biogeochemical cycles. Five case studies (delta 15N measures of N2 fixation; the global carbon cycle and the CO2 problem; sulphur and acid deposition; use in archaeology; and detrital organic matter in saltmarshes) show how stable isotope measurements can provide crucial information for ecosystem analysis.-P.J.Jarvis