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A study of autumnal postmigrant weights and vernal fattening of North American migrants in the tropics
... Spring migration sees a reduction in species richness in the region, and many transient species on route from South America, appear to be carrying sufficient reserves on arrival to reach North America without refuelling . For a smaller number of Central American wintering species, fuel loads, recapture rates and fuel deposition rates point to a stopover both on the Yucatan Peninsula and in south-eastern Mexico, including species of concern such as Wood Thrush Hylocichla mustelina and Kentucky Warbler Geothlypis formosa (Rogers and Odum 1966, Shaw and Winker 2011. ...
... Costa Rica and Panama -Stopover studies from Costa Rica and Panama are also surprisingly rare, and aside from those dating back 50 years (Rogers and Odum 1966) and a recent study on Swainson's Thrush Catharus ustulatus (Wilson et al. 2008), we could find no reference to the stopover behaviour of Nearctic-Neotropical migrants in this region. There is, however, a longterm migration monitoring station at Tortuguero, Costa Rica (Elizondo-Camacho and Ralph 2012), and the data collected there would no doubt shed light on the use of the Caribbean lowlands for stopovers, beyond the habitat selection inferences thus far reported (Wolfe et al. 2014). ...
... Cerulean Warbler) may depend on montane forest habitats in Costa Rica and Panama, especially in early autumn. Studies of autumn migrants on the Caribbean coast of Panama found a mixture of exhausted birds and individuals with sufficient reserves to continue their migration well into South America (Rogers 1965, Rogers andOdum 1966). There was some evidence that fueldepleted birds stopped over in Panama to rebuild their energy reserves (Galindo et al. 1963). ...
Nearly 300 species of landbirds, whose populations total billions, migrate between the Neotropics and North America. Many migratory populations are in steep decline, and migration is often identified as the greatest source of annual mortality. Identifying birds’ needs on migration is therefore central to designing conservation actions for Nearctic-Neotropical migratory birds; yet migration through the Neotropics is a significant knowledge gap in our understanding of the full annual cycle. Here, we synthesise current knowledge of Neotropical stopover regions and migratory bottlenecks, focusing on long-distance, migratory landbirds that spend the boreal winter in South America. We make the important distinction between “true” stopover—involving multi-day refuelling stops—and rest-roost stops lasting < 24 hours, citing a growing number of studies that show individual landbirds making long stopovers in just a few strategic areas, to accumulate large energy reserves for long-distance flights. Based on an exhaustive literature search, we found few published stopover studies from the Neotropics, but combined with recent tracking studies, they describe prolonged stopovers for multiple species in the Orinoco grasslands (Llanos), the Sierra Nevada de Santa Marta (Colombia), and the Yucatan Peninsula. Bottlenecks for diurnal migrants are well described, with the narrowing Central American geography concentrating millions of migrating raptors at several points in SE Mexico, Costa Rica, Panama and the Darién. However, diurnally migrating aerial insectivores remain understudied, and determining stopover/roost sites for this steeply declining group is a priority. Despite advances in our knowledge of migration in the Neotropics, we conclude that major knowledge gaps persist. To identify stopover sites and habitats and the threats they face, we propose a targeted and collaborative research agenda at an expanded network of Neotropical sites, within the context of regional conservation planning strategies.
... The usefulness of wing length in conjunction with body mass for estimating the fat content of individual nocturnal passefine migrants is well established for some species (e.g. Connell et al. 1960, Rogers and Odum 1964,1966). ...
... Averages were significantly higher for the four species on the Isthmus of Tehuantepec (0.025 < P < 0.05 for the Wood Thrush; P < 0.001 for the other three species; t-test). Mass values may not be directly comparable between the two sites for two reasons: (1)Rogers and Odum (1966) held their birds before weighing to reduce gut contents (differences, therefore, are not all fat); and (2) individuals of the three species wintering in the respective areas may represent different populations (apparent differences may be partly due to dissimilarities in size). Nevertheless, the comparison is valuable.The possibility that gut contents contribute to the differences observed is real. ...
... erved is real. However, even if guts were full at weighing on the Isthmus (generally not the case; pers. obs.), subtraction of a full gut (ca. 4.5% of body mass; Baldwin and Kendeigh 1938) renders only the difference observed in the Wood Thrush questionable (4.5% of mean body mass is 1.99 g). Differences in the other three species are rather large.Rogers and Odum (1966) found that Gray Catbirds and Ovenbirds in Panam• showed an average mass that was actually lower than the fat-free mass of each species: individuals of these two species were generally fat-depleted. Although possible size differences cannot be addressed, individuals of these two species were fatter on the Isthmus of Tehuantepec. Only 18. ...
The Isthmus of Tehuantepec in southern M6xico seems to cause a concentration of Nearctic-Neotropic mi • ;rant landbirds during migration. Despite its possible importance as an area for fat deposition, almost nothing is known about how this area is used by migrants. Of 11 small passefine species examined, 6 showed significant diurnal increases in body condition in relation to time of capture. All six showed gains suggesting low to moderate levels of fat deposition, concordant with the concept of the Isthmus as an important source of stopover resources. The area is not used in the same manner by all of these common species, however. The migrants at this site in autumn probably have not arrived via a long-distance, trans-Gulf migration. Comparison with data from other sources suggests that the energetic costs of molt are important at northerly stopover sites, and that modifications are needed in our concepts of Middle American migration routes. Received 8 February 1994, accepted I April 1994.
... Such body mass loss could be linked with capture stress, causing deterioration of individual body condition following ringing (e.g. Rogers & Odum 1966;Leberman & Stern 1977;Clausen & Madsen 2014;reviews in Clark 1979;Duarte 2013). The Tour du Valat traps used seed bait to attract ducks (see description of the Camargue technique in Bub 1991), however, so an alternative problematic if it causes ringed birds to behave in a way that differs from the population as a whole. ...
... Earlier studies documenting such handling traumatism causing reduction in body mass often concerned small passerines (e.g. Rogers & Odum 1966;Leberman & Stern 1977), but a recent study documented similar temporary loss of body condition after marking in Pink-footed Geese Anser brachyrhynchus (Clausen & Madsen 2014). Whether or not birds loose mass due to stress after handling may therefore be species-specific, and not simply related to body size (see also Casas et al. 2015). ...
Studies of waterbirds rely to a large extent on ringing and resighting or recapture data, whilst assuming that ringed birds are broadly representative of the population as a whole. This may not be the case if the capture process may in itself have an influence on the birds. The analyses presented here showed that the body mass of ringed ducks often decreases between capture and recapture if the latter occurs within a few days or weeks. This could possibly reflect stress caused by handling, which would be problematic if it causes ringed birds to behave in a way that differs from the population as a whole. Alternatively, body mass measurements could also be biased by the general use of bait to attract birds to the trap. Initial and subsequent body mass data recorded for Eurasian Teal Anas crecca caught then recaptured within three weeks were compared between sites where the birds were attracted to traps with bait or with live decoys. When bait was used individuals had a greater body mass at ringing but were lighter at recapture at all but one site, where only a marginal difference was found. Conversely, when using live decoys, body mass remained constant at the next capture event. This suggests that mass loss commonly observed between capture and recapture is not caused by handling, but is potentially an artefact linked to duck hyperphagia in the presence of abundant food at ringing. It also implies that most available duck body mass data, which are usually obtained from birds ringed at baited traps, may be artificially inflated. The present results are based on one single unbaited site, however, and experimental manipulative studies (alternating the use of bait and live decoys to trap birds) are needed to confirm the findings.
... By contrast, most Veery arrive on the northern coast of Colombia after crossing the Caribbean from the southeastern United Sates (González-Prieto et al. 2011, Heckscher et al. 2011, Bayly et al. 2012. They are uncommon fall migrants in Central America but sometimes appear in large numbers along the Caribbean coast from Belize to Panama (Rogers and Odum 1966, Remsen 2001, eBird 2014. The species winters in southern Amazonia and as far south as the Pantanal and southeastern Brazil and apparently makes long intrawinter movements (Remsen 2001, Heckscher et al. 2011, eBird 2014. ...
... Information about the fall migration of Gray-cheeked Thrush is scarcer. The few fall records from the Sierra Nevada de Santa Marta, Venezuela, and the Guyanas , eBird 2014, and reports of relatively large numbers of birds during the fall in Panama (Galindo et al. 1963, Rogers andOdum 1966), suggest that this species has a prevailing Central American route into South America. Wintering grounds are believed to be primarily in the northwestern Amazon basin, extending to the base of the Colombian and Venezuelan Andes (Hilty andBrown 1987, Hilty 2003, N. J. Bayly andC. ...
Northern South America is a geographic bottleneck that may be limiting the survival of Nearctic–Neotropic migrants. However, very little is known about the migration ecology of transcontinental migrants wintering in South America. We studied the fall migratory strategies of three species of thrush (Catharus ustulatus, C. fuscescens, and C. minimus) at 2 major migrant gateways into South America: the Dari´en and the Sierra Nevada de Santa Marta (SNSM) of northern Colombia. Assuming that migration route shapes the stopover strategy of birds and that our sites receive birds from 2 different routes, we predicted that (1) migrants travelling over land through Central America (Dari ´en) would make short and frequent stopovers followed by short flights and (2) migrants crossing the Caribbean (SNSM) would make few and long stopovers to acquire fuel for longer flights. To test these predictions, we estimated condition on arrival, stopover duration, fuel deposition rates, and potential flight ranges after stopover, using 3 yr of capture–recapture data. Each species adopted a different stopover strategy, with Swainson’s Thrush arriving in South America through the Darién,
making the shortest stopovers and achieving the shortest flight ranges (800 km); Gray-cheeked Thrush arriving primarily through the Dari´en, making short stopovers but achieving longer flight ranges (1,200 km); and Veery arriving in both the Dari´en and the SNSM, making the longest stopovers and achieving the longest flight ranges (1,900 km). Our results suggest that stopover strategies are shaped by both migratory route (over land vs. over water) and distance to final destination in South America. Unravelling the breeding origins and wintering destinations of individuals passing through northern Colombia would greatly improve our understanding of hemispheric migration systems and will be critical if we are to protect the most important stopover sites and habitats.
... Land availability for these birds during spring migration increases rapidly north of the Isthmus of Tehuantepec. Several studies have addressed refueling and stopover ecology during autumn on this isthmus and farther south in Middle America (Galindo et al. 1963;Galindo and Mendez 1965;Rogers and Odum 1966;Child 1969;Winker 1995a, b;Johnson and Winker 2008), but there are few reports of work conducted in spring (e.g., Galindo et al. 1963, Wilson et al. 2008. ...
... (Linear regressions of wing chord on time of day showed no significant relationships for any species examined.) Mass has been shown in fat-free mass studies to correlate with fat carried (Rogers 1965, Rogers andOdum 1966). The underlying assumption is that condition index is correlated with amount of fuel carried. ...
The narrowing of the North American continent at the Isthmus of Tehuantepec creates an important geographic bottleneck for songbirds on their northward spring migrations. The Sierra de Los Tuxtlas, in the northwestern portion of the Isthmus, provide an ideal location from which to address questions of resource use and fuel acquisition during migration. We operated mist nets during morning and evening to capture passerines during spring migration in 2003 and 2004. Seven of 13 taxa had significant diurnal increases in body condition (an index of size-adjusted mass): Swainson's Thrush (Catharus ustulatus), Wood Thrush (Hylocichla mustelina), Magnolia Warbler (Dendroica magnolia), Kentucky Warbler (Oporornis formosus), Hooded Warbler (Wilsonia citrina), Worm-eating Warbler (Helmitheros vermivorum), and Ovenbird (Seiurus aurocapilla). All of these species, except Ovenbird, also had a significant increase in fat score. Indigo Buntings (Passerina cyanea) had a significant increase in fat score but not in condition index. A comparison with autumn migration at this site showed overall similarities in percentage of species gaining mass and in the amount gained, but there were seasonal differences within species. There was no relationship between increase in body condition and a mainland versus trans-gulf migratory strategy.
... By contrast, most Veery arrive on the northern coast of Colombia after crossing the Caribbean from the southeastern United Sates (González-Prieto et al. 2011, Heckscher et al. 2011, Bayly et al. 2012. They are uncommon fall migrants in Central America but sometimes appear in large numbers along the Caribbean coast from Belize to Panama (Rogers and Odum 1966, Remsen 2001, eBird 2014. The species winters in southern Amazonia and as far south as the Pantanal and southeastern Brazil and apparently makes long intrawinter movements (Remsen 2001, Heckscher et al. 2011, eBird 2014. ...
... Information about the fall migration of Gray-cheeked Thrush is scarcer. The few fall records from the Sierra Nevada de Santa Marta, Venezuela, and the Guyanas , eBird 2014, and reports of relatively large numbers of birds during the fall in Panama (Galindo et al. 1963, Rogers andOdum 1966), suggest that this species has a prevailing Central American route into South America. Wintering grounds are believed to be primarily in the northwestern Amazon basin, extending to the base of the Colombian and Venezuelan Andes (Hilty andBrown 1987, Hilty 2003, N. J. Bayly andC. ...
Hourly mass gain during migratory stopover in spring and fall was estimated for 48 species at three sites on Long Point, Ontario. Estimates were based on regression of size- corrected mass at first capture on time of day. Mean mass gain for all species and sites in fall was 0.61% of lean body mass/h, well over the mean estimated gain required to maintain daily energy balance (0.27% of lean body mass/h). In spring, mass gain was 0.50% of lean body mass/h at two sites but only 0.17% at the extreme tip of Long Point, where cold lake temperature in spring probably affects insect abundance. While most species fared well in fall, thrushes did not, perhaps due to poor habitat for ground foraging on Long Point. Except for the eastern tip of Long Point in spring, the study sites compare favorably in mass gain to two other stations in the northern U.S. where similar analyses have been done. CAMBIOS EN MASA DURANTE PARADAS EN LA MIGRACION: UNA COMPARACION DE GRUPOS DE ESPECIES Y LOCALIDADES
... Few studies have addressed energetic needs (Rogers and Odum 1966;Child 1969;Winker 1995a, b), and there are no published studies of migrant stopover ecology near the Gulf of Honduras. We chose a site near the Gulf of Honduras in lowland tropical forest to examine the autumn migration of Nearctic-Neotropic migrants. ...
... The high levels of fat observed at our site may be in preparation for a longdistance migratory flight, rather than shorter flights south through Central America. The emaciated migrants observed by Rogers and Odum (1966) in Panama would seem to suggest they arrived from a great distance, also supporting the possibility of longer flights over Central America, rather than shorter flights through it. Mass gain data from farther south in Central America would be useful in elucidating this situation. ...
The southeastern Yucatan Peninsula hosts high numbers of transient Nearctic-Neotropic migrants during autumn migration, but the importance of this region during migratory stopover has not been addressed. We studied autumn stopover body mass gains among passerine migrants in tropical lowland forest 20 km inland from the Gulf of Honduras. Most individuals captured had some subcutaneous fat. Ten of 15 taxa with sufficient sample sizes had significant positive diel (24 hr) gains in a body condition index. Estimates of net mass gains in these 10 taxa suggested they all were depositing fat; average individuals in four of these taxa were depositing sufficient fuel to undertake an entire night of migration after only 1 day of fattening: Empidonax spp., Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Northern Waterthrush (Seiurus noveboracensis). Two (Wood Thrush [Hylocichla mustelina] and Common Yellowthroat [Geothlypis trichas]) of the four species apparently not gaining mass at the study site migrate late in the season and occurred only after Hurricane Iris severely altered the habitat. Four other species (Gray Catbird, Magnolia Warbler [Dendroica magnolia], American Redstart [Setophaga ruticilla], and Indigo Bunting [Passerina cyanea]) had significant gains in mass after the hurricane. These data demonstrate the importance of the region as an autumn stopover site for some species and suggest that stopover areas farther north are also important to migrants passing through the southeastern part of the Yucatan Peninsula.
... Since metabolic rate per gram of fat-free weight appears to be similar among passerines of 10 -40 g [5], the flight range of a bird with a given amount of fat can be estimated. Several authors [21,22] agree that, during stopover all of the mass gain results from fat storage. Therefore, this increase in body mass (g) was first converted into energy equivalents by considering the energy value of fat to be 39.8 kJ g -1 [23]. ...
... Therefore, this increase in body mass (g) was first converted into energy equivalents by considering the energy value of fat to be 39.8 kJ g -1 [23]. Secondly, different empirical data were used to estimate flight metabolism in skylarks [22][23][24][25][26][27]. The most basic estimate was given by Nisbet et al. [24] with a consumption of fat by passerines at a rate of about 1% of their body mass per hour during migratory flight. ...
Mist-nettings of Eurasian skylarks (Alauda arvensis) were conducted throughout the day near the coastline in south-western France during the fall migratory period. The main objective of this work was to document some aspects of body condition (mass and fat stores) in skylarks. Between 1997 and 2004, a total of 8903 birds were captured in October-November. The median capture dates of fall migrations for females and males were October 24 and October 26, respectively. About 58.4% and 34.0% of birds were females and males respectively, the remaining 7.6% corresponding to unsexed birds. Skylarks arrived to our study site with low fat stores, 42% of the individuals showing no visible fat deposits. Rates of mass changes were found to be positively related to the time of day: individuals captured during the night before 07:00 were 3-4% heavier than individuals captured during daylight between 07:00 and 20:00. On the daytime, the average rate of body mass gain was about 5% for both sexes, suggesting that migratory birds were not only able to gain energy for their regular metabolism, but they were also able to store fat for migration. According to allometric equations to estimate the energetic cost of flight, flight ranges for the majority of birds were estimated to be less than 180 - 240 km for females and lower than 160 - 220 for males. As migratory stopover sites are used for refuelling by many migrant land birds, our data suggest that most of the skylarks might exhibit a « feed-by-day, fly-by night » strategy in our region, highlighting the need for preserving stopover sites, such as those encountered in south-western France, for successful migration. Considering that many migrant birds such as skylarks feed heavily on seeds, changes in agricultural practices might affect survival capabilities of skylarks during their fall migration and in winter.
... Since metabolic rate per gram of fat-free weight appears to be similar among passerines of 10 -40 g [5], the flight range of a bird with a given amount of fat can be estimated. Several authors [21,22] agree that, during stopover all of the mass gain results from fat storage. Therefore, this increase in body mass (g) was first converted into energy equivalents by considering the energy value of fat to be 39.8 kJ g -1 [23]. ...
... Therefore, this increase in body mass (g) was first converted into energy equivalents by considering the energy value of fat to be 39.8 kJ g -1 [23]. Secondly, different empirical data were used to estimate flight metabolism in skylarks222324252627. The most basic estimate was given by Nisbet et al. [24] with a consumption of fat by passerines at a rate of about 1% of their body mass per hour during migratory flight. ...
Mist-nettings of Eurasian skylarks (Alauda arvensis) were conducted throughout the day near the coastline in south-western France during the fall migratory period. The main objective of this work was to document some aspects of body condition (mass and fat stores) in skylarks. Between 1997 and 2004, a total of 8903 birds were captured in October-November. The median capture dates of fall migrations for females and males were October 24 and October 26, respectively. About 58.4% and 34.0% of birds were females and males respectively, the remaining 7.6% corresponding to unsexed birds. Skylarks arrived to our study site with low fat stores, 42% of the individuals showing no visible fat deposits. Rates of mass changes were found to be positively related to the time of day: individuals captured during the night before 07:00 were 3-4% heavier than individuals captured during daylight between 07:00 and 20:00. On the daytime, the average rate of body mass gain was about 5% for both sexes, suggesting that migratory birds were not only able to gain energy for their regular metabolism, but they were also able to store fat for migration. According to allometric equations to estimate the energetic cost of flight, flight ranges for the majority of birds were estimated to be less than 180 - 240 km for females and lower than 160 - 220 for males. As migratory stopover sites are used for refuelling by many migrant land birds, our data suggest that most of the skylarks might exhibit a « feed-by-day, fly-by night » strategy in our region, highlighting the need for preserving stopover sites, such as those encountered in south-western France, for successful migration. Considering that many migrant birds such as skylarks feed heavily on seeds, changes in agricultural practices might affect survival capabilities of skylarks during their fall migration and in winter.
... We found strong evidence that lower lean mass leads to longer stopover duration in Northern Waterthrush, presumably to rebuild muscle or organ masses, as has been shown in other species (Biebach, 1998;Carpenter et al., 1993;Karasov & Pinshow, 1998). Average lean mass of Northern Waterthrush on first capture was nearly 3 g (~20%) lower than previously estimated (Cano et al., 2020;Rogers & Odum, 1966), and the large range in lean mass (9.05 g-13.98 g) may indicate that Northern ...
During the long‐distance migratory flights of birds, lean mass breakdown occurs in concert with fat catabolism and is expected to have repercussions on total stopover duration because birds require time to rebuild lean tissue before accumulating fat reserves. Despite this, little is known about the role of in‐flight lean mass breakdown on stopover duration because direct measurements are restricted by the destructive nature of traditional body composition analysis and the technological limitations of tracking small birds over large expanses.
We used non‐lethal, non‐invasive Quantitative Magnetic Resonance technology and plasma metabolite profiling to measure the body composition and physiological state of free‐living birds captured at a migratory stopover site after flight across the Gulf of Mexico, and an automated radiotelemetry array covering ~5000 km² to track stopover duration and regional movements. We tested whether stopover duration is prolonged in individuals arriving with lower lean mass and investigated how lean mass affects regional movements.
Stopover duration decreased by 22% for each additional gram of lean mass in Northern Waterthrush (Parkesia noveboracensis), but this relationship was not apparent in Swainson's Thrush (Catharus ustulatus), Grey‐cheeked Thrush (Catharus minimus) or Yellow‐billed Cuckoo (Coccyzus americanus), even though these species also arrived with depleted lean mass. Stopover duration increased for Swainson's Thrush with higher plasma uric acid, a marker of protein catabolism. Northern Waterthrush with higher plasma triglycerides had longer stopover duration.
Our findings suggest that migratory birds may compensate for substantial lean mass losses by increasing refuelling rate or moving to a different stopover site, and highlights species‐level differences in lean mass breakdown and the associated impacts on physiological function. Our results highlight the strategies used by different species to recover from a trans‐Gulf of Mexico flight and resume migration, which improves our understanding of the annual cycle of migratory birds.
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... Physiological studies of migratory landbirds following endurance flights have revealed remarkable adaptations, including partial consumption of the gastrointestinal tract and extensive flight muscle catabolism, which provide essential components of fat metabolism, emergency fuel and facilitate dehydration avoidance (Biebach 1998, McWilliams and Karasov 2001, Schwilch et al. 2002, Biebach and Bauchinger 2003, Gerson and Guglielmo 2011. These physiological changes, coupled with oxidative stress (Jenni-Eiermann et al. 2014), often result in migrants arriving in an emaciated state (Rogers andOdum 1966, Newton 2006). We hypothesize that associated reductions in digestive capacity and flight muscle efficiency Karasov 2001, Gerson et al. 2020), coupled with the slower speed at which lost protein can be replaced relative to fat stores (Smith and McWilliams 2010), will induce behavioral changes in emaciated birds to facilitate the rebuilding of essential protein structures and repair oxidative damage (Eikenaar et al. 2020; for alternative strategies, see Weber and Hedenström 2001). ...
Nonstop endurance flights are a defining characteristic of many long-distance migratory birds, but subsequent recovery phases are not typically distinguished from fueling phases (collectively “stopovers”), despite endurance flights inducing marked physiological changes including flight muscle atrophy and gastrointestinal tract reductions. Here, we hypothesize that recovery requires unique behavioral adaptations, leading to departures from the predictions of optimal migration theory for time-minimizing migrants. We predict that recovering birds will (1) select (moist) food-rich habitats on arrival; (2) have slow initial fueling rates due to decreased gastrointestinal capacity; (3) show a negative correlation between stopover duration and arrival condition instead of a negative correlation with fuel deposition rate (FDR); (4) stopover longer than required to store energy reserves for subsequent flights; and (5) show evidence of rebuilding flight muscles. To test these predictions, we studied Blackpoll Warblers (Setophaga striata) in northern Colombia following trans-oceanic flights >2,250 km. Birds selected dry seasonal habitats, despite the proximity of moist forests, and among 1,227 captured individuals, 14–21% were emaciated and 88% had atrophied flight muscles. We recaptured 74 individuals, revealing net positive mass gains and, contrary to prediction (2), no evidence for slow initial recovery rates. Contrary to prediction (3), stopover duration was only weakly correlated with arrival condition and birds with high FDR (4.9% lean body mass day–1) had shorter durations (3 days) relative to birds with slower rates (7 days): both groups accumulated sufficient fuel to reach nonbreeding (over-wintering) grounds 500–1,000 km away. Mass increases were largely attributable to fat deposition but some birds improved flight muscle condition (31.9%), consistent with prediction (5). Together these results reveal a strong selection for time-minimization in the decisions made by Blackpoll Warblers following trans-oceanic flights, likely mediated through advantages to early arrival on nonbreeding grounds, contrary to our hypothesis of recovery imposing unique selection pressures.
... a "bottleneck" (c.f.Bayly et al. 2018) for NeotropicalMigrants. However, our findings identified only Costa Rica as an area of importance during migration, although there is a small region that was approaching significance around the Gulf of Montijo, suggesting that Panama is also a migratory bottleneck (c.f.Bayly et al. 2018;Mehlman et al. 2005).Rogers and Odum (1966) hypothesized that Panama was an essential stopover region during migration because of the emaciated state of the birds arriving there during Studies focusing on the stopover behavior of Neotropical migrants within Hispaniola are extremely rare(Bayly et al. 2018). The occurrence of Veeries on the Dominican Republic was confirmed by the N ...
Nearctic-Neotropical migrant passerines have experienced population declines
presumably largely due to habitat loss and degradation on both the wintering and breeding grounds. Only recently have these declines been attributed in part to the loss of suitable stopover sites available during migration. Stopover sites of high ecological quality are essential along an ecological barrier in order to provide areas for migrants to rest and refuel. The identification and conservation of high quality stopover sites has become a research priority; however, until recent advances in technology it was difficult to identify these sites without quantitative field surveys. Archival light-level geolocators are the only technology that allows ornithologists to recreate the daily positions of small songbirds (<50g) throughout their annual cycle. The focus of the present
research was to further our knowledge of the annual movements of the Nearctic-Neotropical migratory species, the Veery (Catharus fuscescens), through the use of miniaturized tracking technology. My objectives were to (1) identify important stopover regions used by migrating Veeries, and (2) identify important migratory flyways between the Veery’s breeding and wintering grounds. I used kernel density estimations and hot spot analysis to identify important stopover regions used by two distinct eastern breeding populations and compared the results of the different analyses. I identified differences in stopover regions used during migration on the basis of age, sex, and seasons. I also identified the migratory routes taken by 58 individuals over an eight-year period and found that age and sex did not significantly affect the migratory routes taken during migration; however, I did find that the migratory routes varied greatly between years with respect to the path taken by individuals preparing to cross the Gulf of Mexico. My results highlight the importance of long-term geolocator studies to furthering our understanding of migratory connectivity. Also, through this study, I began establishing a potential framework for the identification of important stopover regions for Nearctic-Neotropical migrants in general. This research will enable conservationists to make more informed decisions regarding the stopover regions to prioritize for protection in future long-term conservation planning efforts.
... However, it is worth noting that these fine-scale eddies (sensu [84]) are unlikely to be exploited by a large soaring bird such as the AWPE. The patterns we found could be partially explained by the fact that birds are in poorer condition during the autumn migration after the breeding season [85,86], which could lead to pelicans taking advantage of the lift generated by turbulence encountered during their flight, as an energy-saving mechanism. Additionally, the higher elevation at northern latitudes provides a source of potential energy, so that the lift by turbulences may be sufficient for gliding down southward during the autumn migration. ...
Energy and time expenditures are determinants of bird migration strategies. Soaring birds have developed migration strategies to minimize these costs, optimizing the use of all the available resources to facilitate their displacement. We analysed the effects of different wind factors (tailwind, turbulence, vertical updrafts) on the migratory flying strategies adopted by 24 satellite-tracked American white pelicans (Pelecanus erythrorhynchos) throughout spring and autumn in North America. We hypothesize that different wind conditions encountered along migration routes between spring and autumn induce pelicans to adopt different flying strategies and use of these wind resources. Using quantile regression and fine-scale atmospheric data, we found that the pelicans optimized the use of available wind resources, flying faster and more direct routes in spring than in autumn. They actively selected tailwinds in both spring and autumn displacements but relied on available updrafts predominantly in their spring migration, when they needed to arrive at the breeding regions. These effects varied depending on the flying speed of the pelicans. We found significant directional correlations between the pelican migration flights and wind direction. In light of our results, we suggest plasticity of migratory flight strategies by pelicans is likely to enhance their ability to cope with the effects of ongoing climate change and the alteration of wind regimes. Here, we also demonstrate the usefulness and applicability of quantile regression techniques to investigate complex ecological processes such as variable effects of atmospheric conditions on soaring migration.
... Pycr']ono1-us goiavier, kep j, overnight without f ood, Among passerines, the proportion of vrater during migratory flight has been variously reported as remaining constant (Odum, Rcgers & Hicks 1964., Child 1969 and belng highly variable (Moreau & Dolp 1970). I,,loutting passe rines ofi.en contain a higher proportion of body vrater than non-moulting birds (Newtolr 196g, Evans 1969), although in shorebirds Evans & Sml th (1975) Rogers & Odum 1966, Johnsto. 1968, chiid 1969) even before lipid reserves have ocen exhausted (Evans 1969 l4any of the normal seasonaf changes in the lean r.;eighl ol shorebirds can also be attribul_ed io changes 1n ihe ieat-l dry weight. ...
... rantes & Pereira (1992) in Costa Rica. Rogers (1966), Smith (1980), Thurber (1980), and Stiles (1994) are the only others to publish reports specifically treating autumn bird migration in Central America, and none studied coastal areas. In nearby southern Mexico, Paynter (1953), Thiollay (1977), Buskirk (1980), and Winker (1995) studied autumn bird migration, but not along the Pacific coast. ...
Autumn bird migration in Central America is poorly known, especially along the Pacific coast. I observed migrating birds at 28 estuaries along the Pacific coast of El Salvador in 1994. At least 19 species appeared to migrate diurnally along the coast: Wood Storks (Mycteria americana) and Brown Pelicans (Peleca-nus occidentalis) were notable as both are frequently considered non-migratory. American White Pelicans (Pelecanus erythrorhynchus) and American Avocets (Recurvirostra americana) may represent regular transients or winter visitors in El Salvador. The rarely reported Collared Plovers (Charadrius collaris) and Elegant Terns (Sterna elegans) were abundant during October and November, perhaps their peak migratory period. I report El Salvador's first photographic documentation for Collared Plover, Stilt Sandpiper (Calidris himanto-pus), and Arctic Tern (Sterna paradisaea), and first sight records for the Chimney Swift (Chaetura pelagica). Accepted 8 August 2002.
... This gave rise to the regression equation: LBM = 3.60 + 0.227*wing length (F 1,41 = 3.93, r 2 = 0.087, P = 0.054). Our LBM estimate for a bird with the mean spring wing length (102 mm), 26.8 g, is in reasonable agreement with an estimate from specimens after fat extraction of 25.7 g (Rogers & Odum 1966), and may better represent the values birds attain after long-distance over-water flights. ...
Stopover sites used to accumulate the energy that fuels migration, especially those used prior to crossing ecological barriers, are regarded as critically important for the survival of Nearctic−Neotropical migratory birds. To assess whether South American stopover sites are used to store the energy required to cross the Caribbean Sea and the Gulf of Mexico to North America by a Neotropical migratory landbird, we studied Gray-cheeked Thrushes in northern Colombia through constant effort mist-netting during spring migration in 2010 and 2011. We combined stopover duration estimates and models of body mass change based on recaptures to estimate departure body mass and potential flight range from our study site. We recaptured 62 birds, the majority of which gained mass. Models indicated significant differences in rates of mass gain between years and age groups and with arrival date. Estimated total stopover durations varied between 15.4 (2010) and 12.5 days (2011). Predicted departure mass ranged between 41.3 and 44.9 g, and potential flight range was estimated at between 2727 and 4270 km. Gray-cheeked Thrushes therefore departed our study site with sufficient energy reserves to cross the Caribbean Sea and the Gulf of Mexico (2550 km). As the first demonstration that birds departing from South American stopover sites can reach North America without refuelling, this has important implications for stopover site protection. Strategic conservation measures in the Sierra Nevada de Santa Marta could protect habitats in which up to 40% of the energy required to complete spring migration is stored by a Neotropical migratory land bird.
... The rate of mass change was estimated by dividing mass change by stopover length (g / day) and by the slope of the regressions between initial capture time and amount of deposited fat. We assumed that water gain or loss was negligible ( Nisbet et al. 1963, Rogers and Odum 1966, Winker 1995. ...
The conservation of long-distance migratory songbirds is complicated by their life-history characteristics and the spatial scales that they traverse. Events during migratory stopovers may have significant consequences in determining the population status of migratory songbirds. Using Wilson's Warbler (Wilsonia pusilla) as a focal species, we investigated effects of age and sex on stopover parameters during spring and fall migration. Variation in stopover patterns was predominantly sex related in spring and age related in fall. In spring, males appeared at study sites earlier than females, and they carried higher fat stores and had lower recapture rates and higher rates of mass gain. In fall, migratory passage overlapped temporally among age and sex classes, but young birds had lower fat stores, higher recapture rates, and longer stopovers than adults. Habitat use differed between spring and fall migration and was affected by the combination of age and sex. Wilson's Warblers appeared to prefer native willow habitat during spring migration. Agriculture field/edge habitats may have represented 'sink habitats' because birds in these habitats tended to be immatures and had a lower rate of fat deposition and longer stopovers. The data suggest that immatures were particularly vulnerable to habitat disturbances at stopover sites during fall migration, probably because of their lower social status and inexperience with long-distance migration. We conclude that knowledge of intraspecific variation in migration strategies is important for effective management of stopover habitats for migratory songbirds.
... Between 21 March and 9 May 1987, 13 individuals of 5 migrating species were found dead in the wooded interior of a coastal island off Louisiana, apparently having starved, and another 66 corpses of 18 species were found on daily walks on a 2-km stretch of beach ). Other instances of birds arriving in Panama in autumn in very poor condition (below fat-free mass) were given by Rogers and Odum (1966), and other severely emaciated birds were collected from oil drilling platforms in the Gulf of Mexico (Gauthreaux 1971). ...
Populations of migratory birds are usually considered to be limited by conditions in breeding or wintering areas, but some
might be limited by conditions encountered on migration. This could occur at stopover sites where competition for restricted
food supplies can reduce subsequent survival or breeding success, or during the flights themselves, when adverse weather can
occasionally kill large numbers of individuals. Competition for food could act in a density-dependent manner and help to regulate
populations, whereas weather effects are more likely to act in a density-independent manner. The evidence for these views
is explored in this paper. When preparing for migration, birds must normally obtain more food per day than usual, in order
to accumulate the body reserves that fuel their flights. Birds often concentrate in large numbers at particular stopover sites,
where food can become scarce, thus affecting migratory performance. Rates of weight gain, departure weights, and stopover
durations often correlate with food supplies at stopover sites, sometimes influencing the subsequent survival and reproductive
success of individuals, which can in turn affect subsequent breeding numbers. Many studies have provided evidence for interference
and depletion competition at stopover sites, relatively few for migration conditions influencing the subsequent breeding or
survival of individuals, and even fewer for effects on subsequent breeding numbers. Migrants in flight occasionally suffer
substantial mortality in storms, especially over water, sometimes involving many thousands of birds at a time. Other mass
mortalities have resulted from atypical ‘winter-like’ weather, occurring soon after the arrival of summer migrants in their
breeding areas or just before their departure in autumn. Again, many thousands of birds at a time have been killed in such
incidents, causing reductions of 30–90% in local breeding densities. In some bird species, migration-related events can at
times have substantial effects on the year-to-year changes in breeding population levels. Nonetheless, the difficulties involved
in investigating migrating birds at different points on their migration routes have so far limited the number of studies on
the influence of events during migration periods on population levels.
... The values for metabolic rate are converted using the equivalent of 39.5kJ/g of fat. We assume that water gain or loss during stopover is negligible, and mass change reflects the variation of the amount of fat deposits [18,21,22] . The likelihood ratio chi-square test was used to see if the recapture rate differed between the spring and the fall and between males and females. ...
The conservation of songbird migrants in China faces challenges similar to those in other parts of the world such as Europe and North America. Songbird migrants have complex life history and are associated with large spatial scale. The events occurred during migration play a critical role in determining population status. Little is known about stopover behavior of migratory songbirds in China during passage, including stopover duration, energetic condition (e.g., the amount of fat stores), and habitat use of these birds. We investigated migration timing, stopover duration, change of energetic condition, and sex-related variations among Red-flanked Bush Robin (Tarsiger cyanurus) at a stopover site in northeast China. A total of 1,751 and 684 Red-flanked Bush Robins were captured in fall 2002 and in spring 2003, respectively. Body mass of fall birds was higher than that of spring birds. Condition index (i.e., body mass adjusted for body size) was lowest among spring females. Birds were more likely to stay longer in fall than in spring. We detected a positive relationship between time of initial capture and condition index regardless of season or sex, suggesting birds were able to replenish energy stores. The net daily mass gain was the highest among males in fall (3% body mass). The net daily mass gain would sustain a flight of 0.6 h for females and 3.1 h for males in fall. The stopover biology of Red-flanked Bush Robins is similar to some songbird migrants of Europe and North America. For example, spring passage time and fat store variation between sexes agree with the hypothesis that males are selected to arrive at their breeding grounds as early as food resources or climatic conditions are adequate in spring. Further research on stopover ecology is urgently needed in China for a better understanding of the migratory behavior and for the conservation of these songbird migrants.
From 1965 to 1970, 15,525 Coal tits were captured at La Golèze pass, situated in the French Alps at approximately 35 Km south of Lac Leman and 3 Km South-West of Bretolet pass. The number and location of mist-nests remained the same throughout each trapping period (mid-august to mid-october) from one year to another. Fat deposits and coloration of the upper parts of a large number of birds were noted, wing length measured, and the weight, age and sex determined.
1) The number of captures varied considerably from year to year despite constant trapping effort : 5408 in 1967 and 9131 in 1969 (years of irruption) ; 209 in 1966 and 537 in 1968 (years of partial migration) ; 162 in 1965 and 71 in 1970 (years of erratic movement).
2) Coloration varied from year to year. In 1968, a year of partial migration, large individuals had grey-green upper parts. In 1969, a year of irruption, small individuals had grey-blue upper parts. In 1970, a year of erratic movements, the large individuals had grey-green upper parts.
The studies of Jouard (1928) and of Snow (1955) suggest that there are a greater proportion of individuals of northern origin in the autumn of years of irruption than in other autumns. Some of the recaptured birds (fig. 11) and field observations of the present study confirm these conclusions. 3) The locations of recapture of 102 coal tits, ringed at La Golèze and Bretolet during irruption years, indicated a winter range which included Languedoc-Roussillon, northern Italy and Italian peninsula. During years of partial migration and erratic movements, no recaptures were recorded.
4) Coal tits invariably migrated at very low altitudes and by sinuous routes, generally following lines of woody vegetation and avoiding mountain obstacles.
5) The dates of passage of Coal tits varies considerably from year to year. The passage was late in years of partial migration (not before October), and early in years of irruption (the end of August).
6) In 1969, the migration of adults preceeded that of immatures by fifteen days.
7) The percentage of adults was very high (42,5 % in 1969 and 23 % in 1967) during irruptions, very low during partial migrations, and very variable during erratic movements.
8) The male/female sex-ratio approximates to 1/1 during irruptions, 1/4 during partial migrations and 1/1 during erratic movements.
9) The dates of passage for males and females did not differ significantly.
10) During irruptions, the dates of passage of Northern populations coincided with the dates of passage of all other individuals.
11) The migration of the Coal tit takes place exclusively during daylight hours. The passage begins around 06.30 hours (local time), attains a maximum at 11.00 hours and decreases throughout the afternoon.
We review ornithology in Belize, formerly British Honduras, since Russell's 1964 monograph and summarize published and unpublished reports, banding records, and museum data. Unpublished reports (gray literature) are an important source of information within the country. Since 1960, there have been numerous studies by the British Forces ornithological societies and others on avian ecology and behavior. the effects of logging on birds, the distribution of overwintering Neotropical migrants (approximately 20% or Belize's avifauna), and comparisons of avian distribution in disturbed versus undisturbed habitat. We review recent distributional records and problematic species records requiring verification and identify distributional "knowledge gaps" Although 70% of the country is stilt dominated by natural vegetation and 20% falls under some form of protected status, certain bird species and families are at risk from human impacts such as habitat conversion, hunting, introduced species, and in some cases, tourism. Areas for future study are suggested.
Although lean migrants are more likely to be recaptured than fatter ones at many stopover sites, the effects of mass loss on the probability of recapture have not been investigated experimentally. During fall mist-netting on Appledore Island, Maine, when two Northern Waterthrushes (Seiurus noveboracensis) or American Redstarts (Setophaga ruticilla) were captured simultaneously, they were divided randomly into control and experimental categories. In the spring, pairs of American Redstarts or Magnolia Warblers (Dendroica magnolia) were treated similarly. Experimental individuals were held without food for up to 6 h before release to investigate the effects of mass loss on the probability of recapture, while control birds were banded and immediately released. Experimental birds significantly decreased in mass during holding. During the fall, experimental individuals were more likely to be recaptured at least 1 d after initial capture than control individuals. However, during the spring, I did not find a difference in recaptures between control and experimental categories, although recapture rates were quite low. These results indicate that mass loss, either directly or as a result of lost foraging time, does lead to extended stopover by migrants during the fall. However, differences in priorities apparently exist between spring and fall migration. During the spring, mass loss may not lead to extended stopovers if migrants have enough energy to continue migration, especially when migrants are close to their final destination.
This book presents an up-to-date, detailed and thorough review of the most fascinating ecological findings of bird migration. It deals with all aspects of this absorbing subject, including the problems of navigation and vagrancy, the timing and physiological control of migration, the factors that limit their populations, and more. Author, Ian Newton, reveals the extraordinary adaptability of birds to the variable and changing conditions across the globe, including current climate change. This adventurous book places emphasis on ecological aspects, which have received only scant attention in previous publications. Overall, the book provides the most thorough and in-depth appraisal of current information available, with abundant tables, maps and diagrams, and many new insights. Written in a clear and readable style, this book appeals not only to migration researchers in the field and Ornithologists, but to anyone with an interest in this fascinating subject. * Hot ecological aspects include: various types of bird movements, including dispersal and nomadism, and how they relate to food supplies and other external conditions * Contains numerous tables, maps and diagrams, a glossary, and a bibliography of more than 2,700 references * Written by an active researcher with a distinguished career in avian ecology, including migration research.
We estimated fat load, length of stopover, and rate of mass change for six Neotropical migrant landbird species at a site along the northern coast of the Gulf of Mexico. Swainson's Thrushes (Catharus ustulatus), Gray Catbirds (Dumetella carolinensis), White-eyed Vireos (Vireo griseus), Red-eyed Vireos (V. olivaceus), Magnolia Warblers (Dendroica magnolia), and American Redstarts (Setophaga ruticilla) were captured on Fort Morgan Peninsula in coastal Alabama during fall migration, 1990 to 1992. In Swainson's Thrushes, White-eyed Vireos, and American Redstarts, adults carried significantly higher fat loads than young birds, whereas no age-related differences in fat loads were evident in the other species. The likelihood of staying beyond the day of capture and the rate of change in body mass did not differ between age classes. One consequence of differences in fat load is reflected in flight range in relation to the Gulf of Mexico. On average, adult Swainson's Thrushes, White-eyed Vireos, American Redstarts, and both age classes of Magnolia Warblers carried sufficient energy stores to complete a trans-Gulf flight, whereas young Swainson's Thrushes, White-eyed Vireos, American Redstarts and both age classes of Gray Catbirds carried insufficient stores for such a flight, based on flight-performance simulations.
We investigated fat deposition in transient, nocturnal, long-distance migrants at a wooded stopover site that is not near an ecological barrier (e.g. desert, large water body). The changes in body mass of recaptured birds have traditionally been used as a measure of mass gains at stopover sites. This technique ignores the majority of transients, however, possibly hindering the ability to answer species-level questions regarding stopover mass gain. We compare an analysis of recaptures with a technique that considers all captures and their condition by time of day. Eleven woodland-associated migrant species were analyzed, as well as a resident species (Black-capped Chickadee, Parus atricapillus) for comparison. Based on recapture data alone, our study site appears to be primarily a location of mass loss, rather than one of fat deposition. Conversely, the examination of condition by time of day suggests that individuals of several species have net daily gains greatly exceeding those of recaptured individuals. During autumn, however, several species exhibited net daily losses. Although some of these losses may be related to molt, it seems unlikely that molt is the only contributing factor. Differences among species in mass gains at our site suggest that various fat-deposition patterns (and, thus, migration strategies) may occur among migrants that are not approaching ecological barriers.
Climatic changes induced by the El Niño—Southern Oscillation (ENSO) commonly influence biological systems; however, climatic variability and multitrophic interactions within tropical latitudes remain poorly understood. We examined relationships between migrant condition and ENSO during spring migration in Costa Rica. Our study is based on correlating an ENSO index with body-condition metrics of six Nearctic—Neotropic migrant bird species during stopover in Costa Rica over a 10-year period. This study is the first to report correlations between El Niño and changes in condition of multiple migrant species. The condition of one insectivore improved, whereas two frugivores experienced reduced condition during El Niño. Our detected correlations suggest that the ENSO cycle may influence changes in migrant mass; such interactions may ultimately affect demographics of certain frugivorous and insectivorous migrant species. Potential future management considerations are discussed in light of global climate change and our findings.
The movements of birds in Middle America are probably the poorest knOWIl aspect of the biogeogTaphy of North American vertebra tell. Neotropical migrants are composed ofintrat:ropical, nearetic-neotropic, altitudinal, and neaustral· neotropic migranU. Individuals of the first three categorie.s are commOD at stopover sites in southern Mnico. The Isthmus ofTehuantepec ill the northernmost narrowing ofthe North American c:ootinentallandmll88, causing a funneling and concentration of nearctic-neotJ'opic landbird migrantll. This paper focuses on woodland birds in this region in autumn, examining abundance (using mil t nets), patterns of movement, community composition, and mass gaina. This avian community is dominated by nearctic-neotropic migrants during October. The preseoce of these migrant.!! might affect the resident community. Resident species are in many cues not ae dentary. From the perspective ofhabilat use, woodland migrants in Los Tuxtlas constitute a heterogeneous assemblage, requiring a wide arrayoihabitat types. Many species seem to deposit fat in migration at this site. In two species, mass deposition is correlated with stopover behavior. It is suggested that migratory route selection is rather poorly known, and the autumn route of the Red-eyed Vireo (Vireo olivaceus) is updated and diaculsed baaed on data from thilstudy and the literature. Without knowledge of distributions, move ments, and habitat selection in neotropical migrants,conservation plans iocusing on thil broad group are not likely to achieve a high degree of success. This knowledge is not likely to be obtained under current research agendas. RESUMEN Los movimientos de aves en Mesoamerica Ion probablemente el aspecto menO!! conocido de la biogeografia de los vertebrados de Norteamerica. Las elpecies migrat.orias neotropica1es estan compuesW de aves migratorias intratropica1es, ndrcticas.neotr6picales, altitudinales, y neaustraJes-neotropica1es. Es oomlin que algunas de las tres primeras categorfas hagan eaca1a en sitios del sur de Mexico. EI Istmo de Tehuantepee esla masa continental mas angosta de la porci6n aurefia de Norteamerica, provoca.ndo un embudo y una c:oncentraci6n de las aves terrestrea migratorias ne4rctiC88-neotropica1es. Elte estudio enfoca el anaIisill de los ~aros migratorios de las tierras OOscosas deestaregi6n en et otofio, STaminando la abundancia (usando rede! de neblina), patrones de movimiento, II composici6n de la comunidad y el aumento de masl. Esla comunidad de aves esta dominada por loa migrantes nelircticos.neotropica1es durante el mes de.octubl'1!. La presencia de estos migrantea puede aiectar a la comunidad de aVeJII reaidentes. Las especies I'1!sidentes, en muchos C88oa, no son sedentarlas. Deade la perspectiva del uso del habilat,103 migratorios de las tierras boecoaaa en Loa Tunlaa coutituyen un conjunto heterogeneo, necesitando un amplio deapliegue de tipos de h'bitats. Mucha. especies parecen depositar grasa en migraci6n en este sitio. En dos especies, la acumulaci6n de masa esta. correlacionada con la conducts en las eBca1as. Se sngiere que la selecci6n de la ruta migratoria es en general poco conocida; y Is ruta otof!.ai del Vine oliu~1U 18 encuentra actualiu.da y Be discute, basada en infonnaci6n del presente estudio y del material publicado. Sin el conocimiento de la distribuci6n, los movimientos, y la selecci6n de habitats en las aves migratorias neotropicalea 103 planes de conservaci6n que se enfoca.n en este amplio grupo no pueden lograr un alto grado de bito. Eate conocimiento no es f'cil de obtener en los temas actuales de investigaci6n. Tbe main obstacle to progress is not ignorance, but the illusion of knowledge.
This study examined the autumnal stopover patterns of migratory passerines on Appledore Island, Maine, from 1983 to 1992. We recaptured 13.4% of migratory passerines at least one day after initial capture with species averages ranging from 2.8% in Eastern Wood-Peewee (Contopus virens) to 33.5% in Philadelphia Vireos (Vireo philadel-phicus). Most observed stopovers were less than four days. Young birds were more prevalent than adults in all species studied. Among Red-eyed Vireos (Vireo olivaceus), Black-and-white Warblers (Mniotilta varia), and Northern Waterthrushes (Seiurus noveboracensis) young birds were more likely to be recaptured than adults. Young Northern Waterthrushes had significantly longer stopovers than adults. No difference in recaptures was detected between the sexes in any species studied. Most of the birds captured were lean (fat class 0 or 0.5) at initial capture. In several species, young birds were significantly leaner both in terms of fat class and mass than adults. Most species studied experienced significant increases in fat class and mass during stopovers. We did not find significant differences in mass or fat increases between age groups or between the sexes in any species studied. Cape May Warblers (Dendroica tigrina), Black-and-white Warblers, and American Redstarts (Setophaga ruticilla) did not exhibit any differences in recaptures, stopover lengths, or mass increases among years. Northern Waterthrushes exhibited significant differences in recaptures and Red-eyed Vireos exhibited differences in recaptures and mass increases among years during this study.
Measurements, weights, and lipid levels of 85 Dunlins collected during two autumn seasons at the Ottenby Bird Observatory in South Sweden were analyzed. Males had significantly shorter wings and bills, and lower body weights than females. Fat depots ranged from about 5 to 30 per cent of total weight and accounted for the major variations in body weight. No correlation was found between body size and lipid level. The water content expressed as a percentage of fat-free weight was virtually constant within each year sample, irrespective of body size and lipid level. Significant differences in fat-free dry weights and water content between the two year samples were found. A formula for calculation of fat stores from total weight and wing length is presented. The results are compared to other work on waders and passerines.
Wing lengths and some major body components were compared among the sexes and age classes of a sample of 48 South Island pied oystercatchers (Haematopus ostralegus finschi). Immature males were significantly lighter in wet weight and fat‐free weight than either immature females or adults, and were significantly lighter than adults in lean dry weight. No statistical differences were found in wing length, total lipids, or fat measure for birds in this sample. In a larger sample of 182 birds, fat measure varied similarly in the age classes, from a low in autumn to a peak in spring just before vernal migration. Massive pre‐migratory fattening typical of many small passerines does not occur in this species, but even so the average fat reserves in spring adults are sufficient for an approximate flight range of 2140 km, well in excess of need. It is hypothesised that the amount of fat deposited before vernal migration is a compromise between the energy cost of acquiring and transporting extra fat and the advantages of arrival at the breeding grounds with sufficient fat reserves for early achievement of breeding condition.
Since 1969 remarkable numbers of night migrants have been attracted during misty conditions in November and December to three 1 kW floodlights at a game viewing lodge on the northeastern side of the Ngulia ridge, a small range of hills in the Tsavo National Park (West), southeast Kenya. The main species involved have been Palaearctic passerines, principally the Marsh Warbler Acrocephalus palustris , the Whitethroat Sylvia communis and the Sprosser Luscinia luscinia.
Data were collected at the Lodge in the late autumns of 1969–71, and in particular between November 1972 and early January 1973, when over 2500 Palaearctic passerines were caught and ringed. Large falls have depended on mist or rain during the latter part of the night, at any time during the month except around full moon. Highest numbers have occurred in late November and the first half of December. In 1973 falls continued into the second week of January. Grounded birds move on quickly, extremely few having been retrapped. During 1972–73, the species prominent in falls at the Lodge were abundant as transit migrants in Tsavo only from mid‐December to early or mid January, at which time retrap rates were highest. The high weights and considerable fat deposits of many birds caught suggested they were grounded some distance north of their destination. Forty‐two migrants analysed had a mean lipid content of 12·9% of their live weight; none was appreciably dehydrated. In 1972–73, highest weights were found at the beginning and end of the season.
Individual species are discussed, and in several cases their African status reviewed. Several species were encountered at Ngulia in numbers far larger than those previously reported from elsewhere in Africa. In 1972–73, for instance, over 1000 Marsh Warblers were caught and many thousands of others seen, hundreds of River Warblers Locustella fluviatilis occurred, and White‐throated Robins Irania gutturalis , Basra Reed Warblers Acrocephalus griseldis , Rufous Bush Chats Cercotrichas galactotes and Olive‐tree Warblers Hippolais olivetorum were caught regularly.
Most of the Basra Reed Warblers, Upcher's Warblers Hippolais languida and Olivaceous Warblers H. pallida , and many of the Whitethroats (apparently all of the eastern race icterops ) handled during late December and early January were in fresh plumage, although these species are not known to moult north of the Sahara. They are presumed to have renewed their plumage in northeast Africa earlier in the autumn. In many Basra Reed Warblers and Whitethroats moult was only partly completed; in almost all such cases it was arrested.
Itinerancy south of the Sahara is discussed. It seems clearly established that a regular southward migration, in the usually accepted sense of the word, occurs across Tsavo, of Palaearctic species which have already been in tropical Africa up to three months. Most species involved in this migration cross the equator on a remarkably narrow front, and are rarely recorded in Kenya west of Nairobi.
A population of 400–600 Acrocephalus orientalis wintering in a Phragmites habitat at 3°N in West Malaysia was studied during four northern hemisphere winters, by means of systematic mist‐netting. Data from other study‐areas, other habitats and other winters are also used.
Intensive mist‐netting appears to have made birds move over longer distances than they did in the absence of disturbance, and to have led to the emigration of marked birds from the study‐area. Trapping also affected feeding behaviour, resulting in weight‐loss; repeated trapping may have increased mortality.
Males and females could be separated by means of wing‐length in fresh plumage. Females were largely confined to Phragmites; males were more numerous on the edge of reed‐beds and in scrub vegetation. Males suffered greater feather‐wear than females.
As measured by the trapping rate, birds were uniformly distributed throughout the Phragmites habitat, at the same density in different winters. Undisturbed birds used a “home‐range” of 1–4 ha, overlapping with 15–50 other individuals. Disturbed birds overlapped with 100–200 others.
Individual birds returned to exactly the same “home‐range” in successive winters. After correcting for the effects of disturbance and incomplete sampling, the proportion of adults ringed in one winter which returned in the next is estimated as 65% in each of two study‐areas. This is a minimum estimate of the annual survival rate for adults.
Mean total body‐weights were at a minimum in midwinter (November‐February). Fat‐free weights were also lower in midwinter than in autumn and spring.
Body‐moult was observed in March and April. Moult of the flight‐feathers takes place between July and September, on the breeding grounds or slightly to the south.
Females departed on spring migration between 10 and 25 May; males some 11–14 days earlier. Adults arrived in autumn between 8 September and 7 October; males and females often came in in separate “waves”. Females were absent for only about 127 days, about the minimum required for migration, breeding and moult.
Dates of migration match those of the more northern breeding populations. Spring departure is later than dates of passage recorded in south China; hence birds of this population appear to make long nights.
On average, birds departing in spring carried about 9 g of fat, roughly 40% of total fat‐free body‐weight. This is about half the energy reserve required for the entire journey. Dates of passage in central China are consistent with a hypothesis that they make the journey (4,500‐5,000 km) in two “hops”.
A few birds which remained light until very late in the spring showed a significantly lower return rate in the next year.
Most birds arriving in autumn appear to have carried 1–2 g of fat, but some were at or below the normal fat‐free weight. Many birds appear to have lost weight soon after arrival.
Returning ringed adults were amongst the very first birds trapped in September. Individual birds appear to have migrated on very similar dates in different years: many of the dates of trapping differed by 2 days or less in successive years.
Trapping rates reached a peak in early October and then declined rapidly, reaching the midwinter level by 21 October. The decline coincided with the differential disappearance of juvenile birds. However, birds collected at this time had adequate fat reserves, and the disappearance appears to have preceded the period of food‐shortage. It is suggested that the loss of juvenile birds resulted from behavioural interactions favouring the more dominant individuals, as has been described for several temperate zone residents.
The first few weeks in the wintering area may thus be the critical period of mortality during the year. Because birds from different breeding areas are expected to be mixed in the winter‐quarters, and vice versa, local mortality factors in winter may affect a number of breeding populations.
High adult survival rates have been recorded in several other birds which breed in the temperate zones and winter in the tropics. In general their breeding success appears to be high, so the first‐year mortality must be high.
The closely related A. arundinaceus , which winters in Africa, differs from A. orientalis in size, wing‐shape, timing of spring migration and timing of moult. These differences can be interpreted as adaptations to different environmental (primarily climatic) factors experienced during migration and on the breeding grounds.
The segregation of males and females into different habitats probably reduces inter‐sexual competition in winter, but this is not necessarily its primary function. Males collected in the evening in Phragmites had smaller fat reserves than females, suggesting that the females are better adapted to this habitat. The large size of the males is probably maintained in part by sexual selection in the breeding season. On the other hand, the size of females and their habitat is probably limited by the specialisation of their nest. These factors would suffice to explain the sexual dimorphism in size and habitat.
Urban parks often represent the only stopover habitats available to migrat-ing birds encountering expansive metropolitan areas. Green spaces remaining within cities may therefore be valuable to migrants; yet studies of migrants in this context are few. I examined the lipid content of birds killed by window collisions in spring and autumn in a small recreational park in New York City to assess the energetic condi-tion of migratory passerines utilizing an urban habitat as a stopover site. I compared chemically determined fat content (expressed as a lipid index: g fat / g lean dry mass) and visible subcutaneous fat scores between seasons, autumn age classes, and birds grouped by family and foraging guild. Average total body fat (as % of dry mass) was 29.4% in spring and 24.1% in autumn; few lean birds were found in either season. Birds in spring were signifi cantly fatter than in autumn. In spring and autumn, no differences in fat content (i.e., fat scores and lipid indices) were observed between warblers and thrushes. In spring, there were no differences in fat content between warbler foraging guilds, whereas in autumn, ground/understory-foraging warbler species were fatter than warbler species associated with arboreal foraging. In autumn, the fat content of imma-ture birds was comparable to that of adults. It could not be determined whether the high fat content of birds found here was acquired during stopovers in the study site or if birds arrived with substantial fat stores remaining from previous stopovers. The likelihood of each scenario and the value of urban parks to migratory birds are discussed.
The Black-capped Chickadee,Parus atricapillus, is a year-round resident of deciduous forests near Ithaca, New York. Chickadees are confronted with high nightly energetic demands, due to their small size (10–12 g) and the subfreezing winter temperatures, which must be met by an adequate energy reserve. The fat stores of Chickadees on midwinter evenings provide slightly more energy then expended overnight, as based on metabolic measurements made in the laboratory.
The Chickadee has a much lower metabolic expenditure overnight than would be predicted for a bird of its size. This is accomplished by regulating nocturnal body temperatures 10–12 °C below normal diurnal body temperature (42 °C). When exposed to 0 °C overnight, Chickadees reduce their hourly metabolic expenditure by 23%.
The nocturnal energetics of the insectivorous Black-capped Chickadee and the granivorous Common Redpoll are compared to illustrate two different strategies for winter residence in the north temperate zone.
The narrow woodlands and wooded barrier islands along the northern coast of the Gulf of Mexico provide the first available landfall for Neotropical landbird migrants after their spring trans-Gulf flight. We studied the timing, volume, fat stores, length of stay, and fat deposition of thrushes (n = 1,903) during stopover at a coastal Louisiana woodland in 1987, 1988, and 1990. Peak migration occurred around mid-April in Wood Thrushes (Hylocichla mustelina) and was one to two weeks later for Catharus thrushes. More than one-third of the thrushes carried no observable subcutaneous fat stores upon initial capture, and only 5% of the birds had estimated fat stores that exceeded 20% of lean body mass. Body mass and condition index (mass/wing length) were negatively related to time of capture, suggesting that birds captured later in the day arrived with lower fat stores. Wing size varied negatively with capture date, suggesting differential migration between sexes and among age classes and/or populations. Recapture probability was related to the amount of fat stores upon initial capture, and length of stay was predictable from estimated fat stores, rate and amount of fat replenishment, and capture date. Flight range estimates suggest that most thrushes captured in spring along the northern coast of the Gulf of Mexico are unable to reach breeding destinations in a single flight. A series of short flights may represent a better migratory strategy than attempting to cover the same distance in one long flight.
Low-virulence Newcastle disease viruses (loNDV) are frequently recovered from wild bird species, but little is known about their distribution, genetic diversity, or potential to cause disease in poultry. NDV isolates recovered from cloacal samples of apparently healthy waterfowl and shorebirds (WS) in the United States during 1986 to 2005 were examined for genomic diversity and their potential for virulence (n = 249). In addition 19 loNDV isolates from U.S. live bird markets (LBMs) were analyzed and found to be genetically distinct from NDV used in live vaccines but related to WS-origin NDV. Phylogenetic analysis of the fusion protein identified nine novel genotypes among the class I NDV, and new genomic subgroups were identified among genotypes I and II of the class II viruses. The WS-origin viruses exhibited broad genetic and antigenic diversity, and some WS genotypes displayed a closer phylogenetic relationship to LBM-origin NDV. All NDV were predicted to be lentogenic based upon sequencing of the fusion cleavage site, intracerebral pathogenicity index, or mean death time in embryo assays. The USDA real-time reverse transcription-PCR assay, which targets the matrix gene, identified nearly all of the class II NDV tested but failed to detect class I viruses from both LBM and WS. The close phylogenetic proximity of some WS and LBM loNDV suggests that viral transmission may occur among wild birds and poultry; however, these events may occur unnoticed due to the broad genetic diversity of loNDV, the lentogenic presentation in birds, and the limitations of current rapid diagnostic tools.
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