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The Orientation of Transoceanic Migrants
... These observers have been amazed to find passerines hundreds of kilometers offshore (Durand 1963(Durand , 1972Casement 1974). Typically, these passerines are in poor condition (McClintock et al. 1978, Williams andWilliams 1990), and a storm is in the area before or at the time of the observation (Bailey 1913, Durand 1963, McClintock et al. 1978. Strangely, most of the passerines observed are thought to be overland migrants (Williams and Williams 1990). ...
... Typically, these passerines are in poor condition (McClintock et al. 1978, Williams andWilliams 1990), and a storm is in the area before or at the time of the observation (Bailey 1913, Durand 1963, McClintock et al. 1978. Strangely, most of the passerines observed are thought to be overland migrants (Williams and Williams 1990). Many ornithologists have concluded that dangerous storms like hurricanes push these birds off course and force those in poor condition to land on ships (Scholander 1955, McClintock et al. 1978). ...
Ornithologists have observed migratory landbirds from offshore ships for over a century. These birds are often in poor condition and thrown off course by storms. We report observations of migratory landbirds on a research vessel that was 320 km offshore in the western North Atlantic Ocean, shortly after Hurricane Gonzalo moved through the area. Between 19 and 25 October 2014, we observed nine passerine species and one falcon species. Two of these passerine species have not previously been observed on offshore ships. We also describe passerine and falcon foraging behaviors that have not been reported before. We examined six passerine birds found dead on the ship and concluded that they likely died of starvation and exhaustion. The passerines we observed may have been disturbed by Hurricane Gonzalo, forcing birds in poor condition to land on the ship. We encourage ornithologists to publish offshore accounts of migratory landbirds to improve our understanding of avian migration.
... Our observations indicate that once the birds had left the coast they usually did not return. This differs from relatively large sea-crossings at the south coast of Spain and on the island of Mallorca (Bruderer and Liechti 1998a) but conforms with various North American studies (review in Williams and Williams 1990), including very long overwater flights such as from the southern tip of Florida (Williams et al. 1977). Birds migrating at high altitudes seem to engage in sea-crossings towards the closest land on the opposite site of the sea (directed towards SW; see Fig. 1), rather than flying in reverse directions to stopover sites further inland in southern Sweden, as was reported for migrants grounded and captured at Falsterbo bird observatory (A , kesson et al. 1996b). ...
... Since the birds allow themselves to be drifted, we assume that for the majority of nocturnal migrants flying above 100 m AGL the local coastline does not serve as a leading line. This is in line with studies at continental coastlines and oceanic islands, where birds have been observed moving on a broadfront without deviations (Williams and Williams 1990). ...
We investigated the patterns of nocturnal bird migration in autumn 1998 at a coastal site on the Falsterbo peninsula in south-western Sweden, by means of a passive infrared device. In total 17 411 flight paths, including track direction and altitude, of migrating birds were recorded for 68 nights from August to October. Mean migratory traffic rate per night varied between 6 and 6618 birds km1 h1, with an average of 1319 birds km1 h1. Migration at Falsterbo showed a similar seasonal pattern to that reported for central Europe, with pronounced peaks of migration and intermittent periods with relatively low migratory intensities. Weather factors explained two thirds of the variance in the intensity of bird migration. During nights with intense migration, associated with weak winds, the mean track direction was close to that in central western Europe (225°). Birds usually maintained a constant heading independent of wind directions and, in consequence, were drifted by the wind. The mean orientation clearly differed from that of the nearest coastline, suggesting that the birds did not use the topography below to compensate for wind drift.
... Virus isolations and antibody studies have established that birds are the major vertebrate host in Australia (Doherty et al., 1966). Many species of birds migrate annually within the Australian continent between the north-west and south-east regions and north-east and south-east regions of Australia (Williams & Williams, 1990). Thus, it seems likely that such species may play an important role in widely disseminating SIN virus in Australia. ...
... Indeed, KUN virus, a flavivirus which is widely distributed in Australia, has also been isolated from mosquitoes collected in Malaysia (Bowen et al., 1970) and JE virus has recently been isolated in the Torres Strait of north-eastern Australia (Hanna et al., 1995). Many species of birds migrate annually between south-east Asia and northern Australia (Williams & Williams, 1990) providing an opportunity for virus spread between these geographic regions by movement of viraemic birds. The identification of a new distinct genetic type of SIN virus circulating in the south-west region of WA was an unexpected result. ...
The molecular epidemiology and evolution of Sindbis (SIN) virus in Australia was examined. Several SIN virus strains isolated from other countries were also included in the analysis. Two regions of the virus genome were sequenced including a 418 bp region of the E2 gene and a 484 bp region containing part of the junction region and the 5' end of the C gene. Analysis of the nucleotide and deduced amino acid sequence data from 40 SIN virus isolates clearly separated the Paleoarctic/Ethiopian and Oriental/Australian genetic types of SIN virus. Examination of the Australian strains showed a temporal rather than geographic relationship. This is consistent with the virus having migratory birds as the major vertebrate host, as it allows for movement of virus over vast areas of the continent over a relatively short period of time. The results suggest that the virus is being periodically redistributed over the continent from an enzootic focus of evolving SIN virus. However, SIN virus strains isolated from mosquitoes collected in the south-west of Australia appear to represent a new SIN virus lineage, which is distinct from the Paleoarctic/Ethiopian and Oriental/Australian lineages. Given the widespread geographic dispersal of the Paleoarctic/Ethiopian and Oriental/Australian lineages, it is surprising that the South-west genetic type is so restricted in its area of circulation. Nucleotide sequence data from the C gene of the prototype strain of the alphavirus Whataroa were also determined. This virus was found to be genetically distinct from the SIN virus isolates included in the present study; however, it is clearly SIN-like and appears to have evolved from a SIN-like ancestral virus.
... It deals with an estimation of species composition of migrants, their numbers, seasonal and daily temporal patterns of passage, height distribution of birds, flight direction and their probable association with weather and mainly wind conditions. An application of standardized quantitative methods for registration of flying birds has already enabled one to get a picture of the spatial and temporal distribution of migrants over the vast territories of North America, Asia and Europe [4][5][6], to detect funnels with high concentrations of birds and to determine what strategies the migrants use to overcome ecologically unfavorable extents such as seas, oceans, deserts and highlands [5,7,8]. ...
... In the sequel it will be called the intensity of migration of The last part of this point will deal with justification the consistency of our model; that is, with checking of compatibility of the requirement of stationarity of measure M postulated in (H5) and the hypotheses (H1)-(H4) about the dynamics of bird flight. For this goal we will construct the stationary dynamic Poisson ensemble of points in the space X with mean measure M which satisfy (8). ...
The study of nocturnal bird migration by cone methods of observation has a century-long history but has continued to be used up to the present. To describe the flux and estimate the number of passing birds a probabilistic model is proposed. This model is based on the concept of dynamic Poisson ensemble of points in appropriate phase space and has two parameters. One is scalar and the other one is functional. We constructed consistent estimations of these parameters and discuss their use for the numerical estimation of the flux of birds observed in a narrow light cone generated by the bright lunar disk and formed by an open angle of telescope. Selection on the same type of birds was suggested as the necessary condition for the model application. Ground speed of each bird was introduced into the model as a new but obligatory value determining the quantification of the flux of bird.
... Although large numbers of migrants opt to fly over land (e.g. the Texas coastal plain; Forsyth andJames 1971, Horton et al. 2019) by taking a circum-Gulf route around the Gulf of Mexico, many birds alternatively take a trans-Gulf route, flying directly across the open water. Migrant strategies that require or involve overwater movements occur in many areas of the globe (Williams and Williams 1990, Diehl et al. 2003, Biebach et al. 2008, Shamoun-Baranes and van Gasteren 2011, but there are few regions that have received the amateur and professional attention bestowed on bird migration through the Gulf of Mexico region. Studies in this region include some of the earliest accounts proposing the likely existence of migratory crossings (Cooke 1904(Cooke , 1905, markedly contrasting views expressed by Williams (1945) and Lowery (1945Lowery ( , 1946, and the first broad application of remote sensing technology to study the diel and seasonal dynamism of bird migration (Gauthreaux 1971). ...
More than two billion birds migrate through the Gulf of Mexico each spring en route to breeding grounds in the USA and Canada. This region has a long history of complex natural and anthropogenic environments as the northern Gulf coast provides the first possible stopover habitats for migrants making nonstop trans‐Gulf crossings during spring migration. However, intense anthropogenic activity in the region, which is expanding rapidly at present, makes migrants vulnerable to a multitude of obstacles and increasingly fragments and alters these habitats. Understanding the timing of migrants' overwater arrivals has biological value for expanding our understanding of migration ecology relative to decision‐making for nonstop flights, and is imperative for advancing conservation of this critical region through the identification of key times in which to direct conservation actions (e.g. temporary halting of wind turbines, reduction of light pollution). We explored 10 years of weather surveillance radar data from five sites along the northern Gulf of Mexico coast to quantify the daily timing and intensity of arriving trans‐Gulf migrants. On a daily scale, we found that migrant intensity peaked an average of nine hours after local sunrise, occurring earliest at easternmost sites. On a seasonal level, the greatest number of arrivals occurred between late April and early May, with peak intensity occurring latest at westernmost sites. Overall intensity of migration across all 10 years of data was greatest at the westernmost sites and decreased moving farther to the east. These findings emphasize the differential spatial and temporal patterns of use of the Gulf of Mexico region by migrating birds, information that is essential for improving our understanding of the ecology of trans‐Gulf migration and for supporting data‐driven approaches to conservation actions for the migratory birds passing through this critical region.
... This genetic conservation in Asia is intriguing for a virus that is known to be maintained only between humans and peridomestic mosquitoes. Additionally, migration routes from India across the Indian Ocean to East Africa have been documented (Williams and Williams, 1990 ...
... The prevailing assumption has been that infected birds can sometimes travel far enough in a short enough period to be effective arbovirus transport agents (Dickerman et al. 1980, McLean 2006, Owen et al. 2006). This belief is probably based, in part, on observations and inferences that landbirds routinely cross 1,000 km or more of inhospitable terrain such as oceans or the Sahara Desert nonstop in 60 h or less of flight time (Blondel 1972, Williams and Williams 1990, Delingat et al. 2008. For example, radar data have suggested that migrant birds leaving the eastern coast of North America may travel to Bermuda in 18 h, to the Caribbean in 64-70 h, and to the northern coast of South America in 80-90 h (Williams et al. 1978). ...
The encephalitic arthropod-borne viruses (arboviruses) can cause a variety of serious human and wildlife diseases, including eastern equine encephalomyelitis, western equine encephalomyelitis, St. Louis encephalitis, Japanese encephalitis, and West Nile neuroinvasive disease. Understanding how these pathogens are dispersed through the environment is important both in managing their health-related impact and in interpreting patterns of their genetic variability over wide areas. Because many arboviruses infect wild birds and can be amplified to a level that makes birds infectious to insect vectors, numerous workers have suggested that the movements of migratory birds represent a major way that these viruses can be transported on a local, continental, and intercontinental scale. Virus transport by birds can, in theory, explain the colonization of new geographic regions by arboviruses, why some arboviruses in widely separated areas are genetically similar, and how arboviruses annually recur in temperate latitudes following interrupted transmission during the winter months. The four scenarios in which a bird could transport an arbovirus include (1) a viremic bird moving while it maintains a viremia sufficient to infect an arthropod that feeds on it at a new locale; (2) a bird previously infected by an arbovirus maintaining a chronic, low-level virus infection that, perhaps because of the stresses associated with annual movement, recrudesces to produce a viremia high enough to infect an arthropod at a new locale or at a different time of year; (3) an infected bird moving and then directly transmitting the virus to other animals either by being preyed upon or scavenged or when other birds contact its saliva or feces; and (4) a bird transporting virus-infected arthropods that drop off at a new location. The idea that birds spread arboviruses is based largely on records of virus-positive birds of unknown movement status caught during the migration season, serological data showing that migrant birds were exposed to virus in the past, and indirect inferences about arbovirus movement based on patterns of genetic variation in viruses in different geographic locations. We review the direct and indirect evidence for these scenarios. Although there are a few records of migrant birds having moved arboviruses over long distances, we conclude that there is no strong empirical evidence that wild birds play a major role in the dispersal of these pathogens at the continental or intercontinental levels or that arboviruses routinely become established at new foci or are seasonally reintroduced into established foci as a result of transport by birds. Additional field and laboratory studies on how virus infection directly affects a bird's likelihood of moving are needed. Researchers interested in virus transport should focus on the extent to which birds move viruses locally and how local transport contributes to arbovirus dispersal more generally, whether virus-infected arthropod vectors disperse long distances, and the extent to which arboviruses are maintained at established foci through vertical transmission and overwintering by adult vectors. Unjustified assumptions that wild birds disperse pathogens could negatively affect the conservation of many migratory species throughout the world and cause public health resources to be diverted into ineffective ways to predict or prevent disease spread.
... They do not seem to detect current flow, and consequently drift off course, reorienting later in the journey [3]. Birds migrating across oceans may also follow a constant compass bearing and do not compensate for wind drift until nearer to the goal (e.g., [1,2,54]). In both cases, these strategies do not prevent migrants from eventually reaching their goal, nor do they directly impact their survival, as would be the case for slow-moving species. ...
Cross-flows (winds or currents) affect animal movements [ 1–3 ]. Animals can temporarily be carried off course or permanently carried away from their preferred habitat by drift depending on their own traveling speed in relation to that of the flow [ 1 ]. Animals able to only weakly fly or swim will be the most impacted (e.g., [ 4 ]). To circumvent this problem, animals must be able to detect the effects of flow on their movements and respond to it [ 1, 2 ]. Here, we show that a weakly swimming organism, the jellyfish Rhizostoma octopus, can orientate its movements with respect to currents and that this behavior is key to the maintenance of blooms and essential to reduce the probability of stranding. We combined in situ observations with first-time deployment of accelerometers on free-ranging jellyfish and simulated the behavior observed in wild jellyfish within a high-resolution hydrodynamic model. Our results show that jellyfish can actively swim countercurrent in response to current drift, leading to significant life-history benefits, i.e., increased chance of survival and facilitated bloom formation. Current-oriented swimming may be achieved by jellyfish either directly detecting current shear across their body surface [ 5 ] or indirectly assessing drift direction using other cues (e.g., magnetic, infrasound). Our coupled behavioral-hydrodynamic model provides new evidence that current-oriented swimming contributes to jellyfish being able to form aggregations of hundreds to millions of individuals for up to several months, which may have substantial ecosystem and socioeconomic consequences [ 6, 7 ]. It also contributes to improve predictions of jellyfish blooms’ magnitude and movements in coastal waters.
... Wind has received more attention and is more integral to optimal migration theory for winged organisms than any other aspect of movement ecology (Alerstam, 1979(Alerstam, , 2011Chapman et al., 2010;Felicísimo, Muñoz, & Gonzáles-Solis, 2008;Gauthreaux, Michi, & Besler, 2005;Liechti, 2006;Liechti & Bruderer, 1998). Because air can move as fast as or faster than most winged organisms, strong selection pressure should favour strategies that undertake migration under advantageous atmospheric conditions (Åkesson & Hedenström, 2000;Alerstam, 1979Alerstam, , 2011Liechti, 2006;Mellone, López-López, Limiñana, & Urios, 2011;Shamoun-Baranes, Bouten, & van Loon, 2010;Shamoun-Baranes & van Gasteren, 2011;Shamoun-Baranes, Leyrer, et al., 2010;Williams & Williams, 1990). The foundation of wind selection and optimal migration theory is rooted in case histories of mostly landbird species that alternate bouts of migration with stopovers to refuel as they move long distances across the landscape (Rappole, 2013). ...
The annual 29 000 km long migration of the bar-tailed godwit, Limosa lapponica baueri, around the Pacific Ocean traverses what is arguably the most complex and seasonally structured atmospheric setting on Earth. Faced with marked variation in wind regimes and storm conditions across oceanic migration corridors, individuals must make critical decisions about when and where to fly during nonstop flights of a week's duration or longer. At a minimum, their decisions will affect wind profitability and thus reduce energetic costs of migration; in the extreme, poor decisions or unpredictable weather events will risk survival. We used satellite telemetry to track the annual migration of 24 bar-tailed godwits and analysed their flight performance relative to wind conditions during three major migration legs between nonbreeding grounds in New Zealand and breeding grounds in Alaska. Because flight altitudes of birds en route were unknown, we modelled flight efficiency at six geopotential heights across each migratory segment. Birds selected departure dates when atmospheric conditions conferred the greatest wind assistance both at departure and throughout their flights. This behaviour suggests that there exists a cognitive mechanism, heretofore unknown among migratory birds, that allows godwits to assess changes in weather conditions that are linked (i.e. teleconnected) across widely separated atmospheric regions. Godwits also showed adaptive flexibility in their response not only to cues related to seasonal changes in macrometeorology, such as spatial shifting of storm tracks and temporal periods of cyclogenesis, but also to cues associated with stochastic events, especially at departure sites. Godwits showed limits to their response behaviours, however, especially relative to rapidly developing stochastic events while en route. We found that flight efficiency depended significantly upon altitude and hypothesize that godwits exhibit further adaptive flexibility by varying flight altitude en route to optimize flight efficiency.
... Despite the documented ornithological significance of the Iberian Peninsula wetlands, studies on the structure and organization of water birds assemblages and their relation to biotic and abiotic factors are limited (Liordos, 2010). In South Portugal, a region well known for its importance for migrating and wintering birds (Williams and Williams, 1990;Berthold et al., 1993;Erwin, 1996), there is some evidence for the importance of small, scattered inland artificial aquatic habitats for water birds (Almeida et al., 2003;Causarano and Battisti, 2009). As this is a Mediterranean region, many of the water bird species are dependent on (around 55) or preferentially associated with (around 28) the availability of inland aquatic environments (Instituto da Água, 2010). ...
Wetlands are considered fundamental for the conservation of many species of birds. They are among the most threatened habitats on Earth, due to area loss through drainage and other land use changes, which lead to large-scale redistributions of birds and population declines. Although anthropogenic activities in wetlands tend to negatively affect water birds, by changing their natural habitat conditions, many species may benefit from the creation of artificial reservoirs, using these areas to feed, breed and rest. Reservoirs and some types of flooded agricultural fields are preferred by many species using Mediterranean extents for wintering and as stopover migration spots. The present paper examined the applicability of a Stochastic Dynamic Methodology (StDM) to predict the dynamics of the daylight water bird assemblages on artificial small reservoirs facing different climatic and hydrological conditions. The final model provided some basis to analyze the responses at community level (total abundance, species richness and behavioural categories) under very complex and variable environmental scenarios. The obtained results show how expected changes in the climatic and hydrological patterns will alter the bird community daylight dynamics, namely their composition and behavioural interactions.
... The Blackpoll Warbler (Dendroica striata) exhibits the most dramatic autumn migration of any Neotropical passerine. This small bird (11–15 g lean body mass) can double its body mass with lipid reserves in preparation for a 4-to 5-day nonstop transoceanic flight over the North Atlantic to winter in South America (Nisbet 1970;Williams and Williams 1990;Nisbet et al. 1995). It has been estimated that Blackpolls have the greatest fuel efficiency during migration compared with other warblers (Hussell and Lambert 1980). ...
L IFE ON OUR PLANET IS intimately tied to its changing seasons. Migratory birds exemplify this with their seasonal comings and goings. Past research programs tended to focus on a single season of the avian annual cycle, but within the last decade we have come to understand that the stages of the annual cycle are deeply interconnected. To understand how an individual fares within a particular stage, we must look at that individual's past and how it prepares for the future. Ecol-ogists, behaviorists, and physiologists now work together to uncover the capabilities and constraints of migratory birds. In this chapter, we look into some of the eco-physiological aspects of the transitional lifestyle of migratory birds, with an emphasis on songbirds because that group has received most of the attention in endocrine studies. It is not our goal to develop a comprehensive survey of avian life history strategies. However, when possible, we describe various hormonal mechanisms involved with activities in different stages of the annual cycle and compare migrants with nonmigrants, and tropical with temperate species. We first present an overview of the stationary periods on the breeding and wintering grounds, and for brevity's sake we have limited this chapter to the well-known monogamous system with bi-parental care. We then discuss behavioral and physiological aspects of energy demand during the periods of transition when all birds prepare or recover from breeding , and as migrants move between the wintering and breeding quarters. Finally, we suggest future horizons for endocrine studies on birds residing in, and moving between , two worlds.
... We conclude that cloud cover along the coast not only causes disorientation by removing or reducing the effectiveness of celestial cues (Griffin 1973, Able 1982, but may also preclude migrants from detecting the coast, thereby increasing the probability of drift over the ocean (Bellrose 197 1; but see Williams and Williams 1990). The marine influence often causes the presence of coastal low cloudiness over SEFI and the immediate coast while at the same time clear skies prevail over most of California (Fig. 2b); thus, both widespread and proximal cloud cover effects, although opposite, can simultaneously contribute to amval. ...
Proximal climatic and lunar effects on amval and departure of nocturnal mi- grant landbirds at Southeast Farallon Island (SEFI), California, were examined using mul- tivariate and univariate statistics. Predictive models including date, weather and lunar variables were developed for both spring and fall, which accounted for 33-40°/o of variation in amval totals and 18-2 1% of vanation in departure proportions. Seasonal, regonal, and taxonomic variation in weather- and lunar-migration relationships were assessed and, along with comparisons of amval and departure patterns, used to differentiate proximal effects on amval to SEFI, from widespread effects resulting in increased migration volume over California. Low wind speeds, low to moderate visibility, full cloud cover and lack of fog viere proximal effects increasing amval to SEFI, while low wind speeds, low but rising barometric pressure, clear and clearing skies, high visibility, and decreased moonlight (in fall) resulted in increased departure proportions and, presumably, caused higher migration volume over the region. Effects of wind direction and air temperature, although related to synoptic weather-migration relationships, generally had obscure or minimal direct influences on amval and departure at SEFI. Departure proportion in spring increased with decreased departure proportion the day before, but few other delay effects between weather variables and amval or departure were found. Seasonal, regional, and taxonomic variation in departure effects were relatively small suggesting that selection of weather-migration strategies has evolved convergently in a diverse group of migrants flying over a region the size of California.
... Statements about flight altitudes based on sea-watch observations have generally been vague; scattered information about species migrating at a particular height may be found in Berndt & Drenckhahn (1974), Camphuysen & van Dijk (1983), Nehls & Zö llick (1990) and Temme (1995). Although radar observations have improved our understanding of bird migration over the North Sea substantially (Lack 1963;Jellmann 1979;Buurma 1987), they have not been able to provide clear information on low-level mig ratory movement until very recently; radar equipment used to date is mostly accurate only at heights above (50) 100-300 m, and it is often not possible to identify birds to species level using radar (Williams & Williams 1990;Berthold 2000). Fo r a long time the intensity of low-level migratory movements over the sea generally were thought -aside from the moult migrat ion of Shelduck Tadorna tadorna-to be of minor importance (cf. ...
During systematic sea watches carried out between 1
September and 15 November 1999 on the East Friesian island of Wangerooge, observations were
recorded of the flight altitude of coastal birds in relation to wind direction and speed. In Red-
throated Diver Gavia stellata, Common Eider Somateria mollissima and Common Scoter Melanitta
nigra the proportion of birds flying into the wind low over the water (0-1.5m) increased with wind
speed. On the other hand, in the same species, the number of low-flying birds decreased in inverse
proportion to the speed of a tail wind and the ratio of birds flying at greater altitudes increased
(1.5-12m and 12-25m respectively). Irrespective of wind speed, the proportion of individual birds
flying low into the wind was highest in Red-throated Diver, Shelduck Tadorna tadorna, Common
Eider and Common Scoter. This pattern is repeated at a higher level in Sandwich Tern Sterna
sandvicensis and Common/Arctic Terns S. hirundo/paradisaea. In contrast, in tail winds, the greatest
proportion of birds of these species invariably flew at the highest levels. Comparisons of flight
altitudes reveal that these species fly noticeably higher in tail winds. This behaviour can be
explained in terms of economy of effort on migration. The present study also reveals that diurnal
movement of the observed species takes place mainly at a low flight altitude (up to 25m,
occasionally up to 50m, rarely higher) above sea level. This demonstrates potentially adverse effects
on birds from construction of proposed offshore wind farms. The data indicate that, to be of any
value in the assessment of the potential disturbance of the wind farms to North Sea migrants, flight
altitude records must be viewed against the background of the meteorological situation as a whole.
... Under such conditions, the North Sea is not a barrier for migration; on the contrary, large-scale synoptic conditions result in an atmospheric 'corridor' facilitating migration . Other studies have also shown that birds take advantage of such large-scale weather systems during transoceanic flight (e.g. Williams & Williams 1990; Felicísimo et al. 2008; Gill et al. 2009). Thus, especially in autumn, when conditions are generally unfavourable for seasonal migration in northwest Europe, we expect selectivity of the appropriate atmospheric conditions to be an important adaptive strategy for numerous migrating taxa, including insects (e.g. ...
Crossing large bodies of water can be extremely risky for terrestrial migrants and yet such migrants have been observed to cross hundreds and even thousands of kilometres of water. However, the mechanisms that enable nocturnal migrants to cross large bodies of water successfully remain unclear. In the north of the Netherlands, autumn migration of birds occurs mainly along a southwesterly axis and can be predicted very successfully. However, on rare occasions, intense and unexpected migration events occur with a significantly different track direction. We hypothesized that these events represent birds arriving from Norway and other Scandinavian countries after crossing the North Sea barrier. We implemented a back-trajectory model calibrated with radar data from autumn 2006-2008 to test our hypothesis, assuming that birds maintain a constant heading and airspeed during flight. A total of 14 events were identified. In some cases measured mean ground speeds were twice as high as mean airspeeds. Model results demonstrated that birds took advantage of atmospheric conditions to cross the North Sea quickly. In the majority of cases, birds could be tracked to Norway, Denmark or Sweden when maintaining a constant airspeed and heading en route, but not in all cases. Thus migrants must be flexible in their reaction to wind to take advantage of dynamic and heterogeneous atmospheric conditions experienced en route. The integration of measurements with simulation modelling provides a powerful framework to improve our understanding of how animals move through a dynamic environment and the consequences of their behaviour.
... In species such as wildfowl that migrate in family groups, migration may be determined largely by culture (Gwinner 1971, Owen & Black 1990. However, the evidence suggests that in many bird species the control of migration is largely genetically determined, with inexperienced migrants finding their wintering areas on the basis of innate spatio-temporal programs (Pienkowski & Evans 1984, Williams & Williams 1990, Wdtschko & Wiltschko 1991, Berthold 1993. Cross-breeding and selective breeding experiments with Blackcaps Sylvia atricapilla and Robins Erithacus rubecula and analysis of genealogies of Song Sparrows Melospiza melodica and Blackbirds Turdus merula have shown genetic determination of various aspects of migration, including the control of obligate migration, whether or not particular individuals migrate in partially migratory populations, the timing and length of the migratory journey and the orientation of migration (Biebach 1983, Schwabl 1983, Berthold 1984. ...
Environmental change through altered climate and land use could have a severe impact on bird populations. Predicting the consequences for the size of bird populations is one of the crucial problems for their conservation. We show how a population model based on the behaviour of individuals can be used to predict the consequences of habitat loss. For a wide range of conditions, loss of either wintering or breeding habitat results in population reduction. The approach is then extended to consider the impact of habitat loss in the wintering area on bird species with complex migratory systems. This shows that ‘knock-on’ effects may occur, so that habitat loss in a wintering area may affect populations which did not initially use that area. The ability to alter migration routes in response to environmental change may be crucial to the future viability of populations. Using a simple model combining genetics and population dynamics, we show that aspects of the biology of a species may affect whether or not its migration strategy is flexible enough to shift in response to habitat change. Some species may be able to adopt new migration routes and avoid the catastrophic consequences of habitat loss in traditional wintering areas; however, other species may lack this flexibility and may suffer severe population declines as a consequence.
... Migrants from the Nearctic and the western Palaearctic can cross barriers along their migration pathways. Nearctic migrants not only cross the Caribbean and Gulf of Mexico (Gauthreaux 1991) but in the autumn many fly out over the Atlantic around the Bermuda high-pressure cell before making landfall in the Antilles or on the northern coast of South America (Richardson 1985(Richardson , 1990Williams and Williams 1990). They are aided by the tail winds generally present at the time of migration, whether in spring or autumn (summarised in Dingle 1996). ...
To broaden perspectives and stimulate research on migration, I survey the bird species that breed in the northern hemisphere and migrate to the southern hemisphere and species that migrate within the southern hemisphere, comparing routes, seasonal patterns and life histories. Differences in the area and latitudinal extent of land masses on the two sides of the Equator influence patterns of bird migration. In contrast to birds breeding in the northern hemisphere, no land or freshwater birds breeding in the southern hemisphere migrate between continents and only a very few cross the Equator. Furthermore, except for shorebirds, few northern intercontinental migrants reach the southern hemisphere in regions south of the equatorial forest belt, because most encounter, and are filtered out by, suitable habitats en route. Australasia is an extreme case because only 10 land or freshwater migrants from the northern hemisphere regularly occur there (most are uncommon or rare) compared with 42 in Africa and 28 in South America, and no Australasian breeders enter Asia beyond Wallace’s Line. Historical geographical and oceanic barriers may be an additional factor limiting migration to Australasia. There are generally no or only slight differences in frequencies of austral migrants within foraging guilds or families across southern continents. Exceptions are rallids, with more migrants in Africa, and cuckoos and nectarivores, with more Old World than New World migrants. Austral migrations are of shorter distances than most of those of the northern hemisphere, and they appear to vary more with respect to routes and patterns. Breeding and non-breeding ranges frequently overlap. Partial migration is common, but there is no evidence that it differs in frequency from that in northern regions. Because climate is generally milder and drier in the southern hemisphere, rainfall is a more important influence on migration than in the north especially in some nomadic birds, but temperature also predicts migration frequency and pathways for many species. These patterns are similar across southern continents, but each continent has its own characteristics. Southern hemisphere migrants seem to display ecophysiologies and orientation mechanisms similar to those found in northern hemisphere species, but very few southern species have been studied. I argue that the variation present among southern hemisphere migrations provides exceptional opportunities to understand the evolution and ecology of migration systems. In order to take advantage of these systems, we need to focus on variation in movement behaviour, on associated syndromes of traits, and on the particular features of natural selection and ecology setting thresholds that lead to the diverse migration patterns observed.
... There is evidence from the field that bad weather, including low temperature, can delay onset, slow down, or even reverse vernal migration in several avian species (e.g., Elkins, 1983;Williams and Williams, 1990). Greater temperature sensitivity of the fattening response in females could reflect some propensity to modify the migratory schedule. ...
We tested the effects of naturally relevant environmental temperatures on long day-induced reproductive development in male and female white-crowned sparrows, Zonotrichia leucophrys gambelii. Transfer from short days (8L 16D) to long days (20L 4D) resulted in rapid testicular development and partial ovarian development as has been reported many times previously. Exposure of experimental groups to low (5 degrees), moderate (20 degrees), and high (30 degrees) temperature during photostimulation had only subtle effects on plasma levels of follicle-stimulating hormone and luteinizing hormone over time and no effects on the size of testes, cloacal protuberance, ovaries, or brood patch at Day 30 of treatment. Long days resulted in the well known increase in body mass and fat score, indicative of preparations for migration. In females, treatment with low temperature resulted in a reduction in the premigratory increase in fat and body mass when transferred to long days. This was accompanied by an increase in plasma levels of corticosterone during the early stages of photostimulation at low temperature. Temperature regimes had no effects on fattening or body mass in males, despite an early increase in plasma corticosterone at low temperature. Circulating levels of thyroxine (T4) and triiodothyronine (T3) increased to varying degrees following photostimulation. Temperature treatment had no effect on plasma levels of thyroid hormones in males, but low temperature did inhibit thyroid hormone secretion (particularly T4) in females. Although reproductive development appears to be resistant to naturally relevant temperature extremes in both sexes, low environmental temperature impaired preparations for migration in females but not males. This effect may be mediated through glucocorticosteroids and not thyroid hormones. Reasons for the sexual dimorphism in this response are unknown, but may be related to sexual selection for males to arrive on the breeding grounds ahead of females regardless of local weather conditions.
... Migratory patterns of both passerines and shorebirds do encompass much of Southeast Asia ranging from the Yellow Sea and South China Sea across the Philippines and Indonesia to Australia. Additionally, migration routes from India across the Indian Ocean to East Africa have been documented (Williams & Williams, 1990). Serological testing of passerines and shorebirds in Southeast Asia could reveal if this is a plausible means of virus dispersal. ...
Chikungunya (CHIK) virus is a member of the genus Alphavirus in the family TOGAVIRIDAE: Serologically, it is most closely related to o'nyong-nyong (ONN) virus and is a member of the Semliki Forest antigenic complex. CHIK virus is believed to be enzootic throughout much of Africa and historical evidence indicates that it spread to other parts of the world from this origin. Strains from Africa and Asia are reported to differ biologically, indicating that distinct lineages may exist. To examine the relatedness of CHIK and ONN viruses using genetic data, we conducted phylogenetic studies on isolates obtained throughout Africa and Southeast Asia. Analyses revealed that ONN virus is indeed distinct from CHIK viruses, and these viruses probably diverged thousands of years ago. Two distinct CHIK virus lineages were delineated, one containing all isolates from western Africa and the second comprising all southern and East African strains, as well as isolates from Asia. Phylogenetic trees corroborated historical evidence that CHIK virus originated in Africa and subsequently was introduced into Asia. Within the eastern Africa and southern Africa/Asia lineage, Asian strains grouped together in a genotype distinct from the African groups. These different geographical genotypes exhibit differences in their transmission cycles: in Asia, the virus appears to be maintained in an urban cycle with Aedes aegypti mosquito vectors, while CHIK virus transmission in Africa involves a sylvatic cycle, primarily with AE: furcifer and AE: africanus mosquitoes.
... The classic case is the departure from eastern North America of small land-birds on a southeastern route following a frontal system. After #ying through the decaying front, the birds get assistance from the trade winds allowing them to reach the coasts of central America (Williams & Williams, 1990; Nisbet et al., 1995). Hence, the departure is triggered by the passage of a weather front with a predictable sequence of wind trajectories. ...
Wind speed and direction have a significant effect on a flying bird's ground speed. Migrants are therefore expected to be sensitive to wind conditions and this should have consequences for optimal strategies of stopover and refuelling. Based on an earlier model of time-minimizing migration which includes wind condition, we investigate the consequences of the temporal correlation of wind conditions. Day-to-day changes in wind conditions are modelled with a two-state Markov process and an expression for the expected speed of migration is derived. The policy of the migrants is described by two parameters: a day t(g) when the birds start to leave whenever favourable conditions occur and a later day t(b)when they leave even in unfavourable winds. The model predicts that in most cases departures should be close to the date which is predicted by a wind-free deterministic model and that the birds should never leave without wind assistance. Only if the probability that the condition remains the same on the following day is close to 1 should the birds leave even in unfavourable conditions shortly after the deterministic optimal date. If the transition matrix is highly asymmetrical, i.e. if it is very probable that unfavourable conditions remain and that favourable conditions will change into unfavourable, then the birds are predicted to start using good winds several days before the deterministic optimal date. An analysis of six years of wind data from two sites in Sweden shows that wind directions on successive days are in fact correlated in all years.
... Many arctic shorebirds are capable of very long nonstop flights (e.g. Williams & Williams 1991;Pennyquick & Battley 2003). Because the energy, time, and safety costs associated with migration ought to increase roughly in proportion with migratory distance (e.g. ...
We analysed migratory connectivity between different winter quarters and breeding sectors in the circumpolar tundra region for arctic shorebirds, in relation to migratory distances and ecological barriers. Total distances and barriers were calculated and measured for all potential migratory orthodrome links between 10 selected winter regions and 12 breeding sectors. The migratory segment between the northernmost stopover site and the breeding area, associated with the entry to and exit from the tundra during spring and autumn migration, respectively, was also identified and measured for each potential link.
The analysis indicated that the evolution of migratory links among arctic shorebirds is constrained not by distance as such but by distance across ecological barriers, possibly because of the complex adaptations required for barrier crossing and extensive detour migration (and in a few cases because barrier distances exceed the birds' theoretical flight range capacity). A particularly pronounced barrier effect of the Arctic Ocean, as apparent from a sharp decline in migratory connectivity between the opposite sides of the Arctic Ocean, may reflect a crucial importance of favourable entry and exit conditions for successfully occupying different sectors of the tundra breeding area by shorebirds from winter regions situated at widely different total distances in both the southern and northern hemispheres.
Populations of the Bar-tailed Godwit (Limosa lapponica; Scolopacidae) embark on some of the longest migrations known among birds. The baueri race breeds in western Alaska and spends the nonbreeding season a hemisphere away in New Zealand and eastern Australia; the menzbieri race breeds in Siberia and migrates to western and northern Australia. Although the Siberian birds are known to follow the coast of Asia during both migrations, the southern pathway followed by the Alaska breeders has remained unknown. Two questions have particular ecological importance: (1) do Alaska godwits migrate directly across the Pacific, a distance of 11 000 km? and (2) are they capable of doing this in a single flight without stopping to rest or refuel? We explored six lines of evidence to answer these questions. The distribution of resightings of marked birds of the baueri and menzbieri races was significantly different between northward and southward flights with virtually no marked baueri resighted along the Asian mainland during southward migration. The timing of southward migration of the two races further indicates the absence of a coastal Asia route by baueri with peak passage of godwits in general occurring there a month prior to the departure of most birds from Alaska. The use of a direct route across the Pacific is also supported by significantly more records of godwits reported from within a direct migration corridor than elsewhere in Oceania, and during the September to November period than at other times of the year. The annual but rare occurrence of Hudsonian Godwits (L. haemastica) in New Zealand and the absence of their records along the Asian mainland also support a direct flight and are best explained by Hudsonian Godwits accompanying Bar-tailed Godwits from known communal staging areas in Alaska. Flight simulation models, extreme fat loads, and the apparent evolution of a wind-selected migration from Alaska further support a direct, nonstop flight.
Atravesando la Barrera Ecológica Final: Evidencia de un Vuelo sin Escala de 11 000 km de Longitud desde Alaska a Nueva Zelanda y el Este de Australia por Limosa lapponica
Resumen. Las poblaciones de Limosa lapponica (Scolopacidae) se embarcan en una de las migraciones más largas conocidas para aves. La raza baueri cría en el oeste de Alaska y pasa la estación no reproductiva a un hemisferio de distancia en Nueva Zelanda y el este de Australia; la raza menzbieri cría en Siberia y migra hacia el oeste y el norte de Australia. Aunque se sabe que las aves de Siberia siguen la costa de Asia durante ambas migraciones, la ruta meridional que siguen las aves reproductivas de Alaska ha permanecido desconocida. Dos preguntas tienen particular importancia ecológica: (1) ¿las aves de Alaska migran directamente a través de Pacífico, a lo largo de 11 000 km? y (2) ¿son capaces de hacerlo en un único vuelo sin parar a descansar y reabastecerse? Exploramos seis líneas de evidencia para responder a estas preguntas. La distribución de avistamientos de aves marcadas de las razas baueri y menzbieri fue significativamente diferente entre vuelos hacia el norte y el sur, sin que hubiera prácticamente un solo avistamiento de individuos marcados de baueri a lo largo del continente asiático durante la migración hacia el sur. El período de la migración hacia el sur de ambas razas indica la ausencia de una ruta costera asiática para baueri, con un pico en el paso de las aves ocurriendo allí un mes antes de la partida de la mayoría de las aves desde Alaska. El uso de una ruta directa a través del Pacífico también está avalado por un número significativamente mayor de aves reportadas para un corredor migratorio directo que para cualquier otro lugar de Oceanía, y para el período entre septiembre y noviembre que para otros momentos del año. La presencia anual, aunque rara, de L. haemastica en Nueva Zelanda y la ausencia de registros a lo largo del continente asiático también avalan la posibilidad de un vuelo directo y se explican mejor por el hecho de que L. haemastica acompaña a L. lapponica desde áreas de escala comunes en Alaska. Evidencia complementaria de un vuelo directo sin escalas está dada por modelos de simulación de vuelo, la gran acumulación de grasa en las aves y la aparente evolución de una migración seleccionada por el viento.
Using the altitudinal profiles of wind, temperature, pressure, and humidity in three flight models, we tried to explain the altitudinal distributions of nocturnal migrants recorded by radar above a desert in southern Israel. In the simplest model, only the tailwind component was used as a predictor of the most preferred flight altitude (T model). The energy model (E model) predicted flight ranges according to mechanical power consumption in flapping flight depending on air density and wind conditions, assuming optimal adjustment of airspeed and compensation of crosswinds, and including the influence of mass loss during flight. The energy-water model (EW model) used the same assumptions and parameters as the E model but also included restrictions caused by dehydration. Because wind was by far the most important factor governing altitudinal distribution of nocturnal migrants, differences in predictions of the three models were small. In a first approach, the EW model performed slightly better than the E model, and both performed slightly better than the T model. Differences were most pronounced in spring, when migrants should fly high according to wind conditions, but when climbing and descending they must cross lower altitudes where conditions are better with respect to dehydration. A simplified energy model (Es model) that omits the effect of air density on flight costs explained the same amount of variance in flight altitude as the more complicated E and EW models. By omitting the effect of air density, the Es model predicted lower flight altitudes and thus compensated for factors that generally bias height distributions downward but are not considered in the models (i.e. climb and descent through lower air layers, cost of ascent, and decrease of oxygen partial pressure with altitude). Our results confirm that wind profiles, and thus energy rather than water limitations, govern the altitudinal distribution of nocturnal migrants, even under the extreme humidity and temperature conditions in the trade wind zone.
Within the animal kingdom, birds are unrivalled at covering large distances quickly and passing over geographic barriers. They use this power to reach food supplies, go where environment conditions are most suitable, and escape predators. Many bird species are migratory and regularly shuttle between winter and summer quarters, which may be far apart. The marked site fidelity of most species both when breeding and in winter, often even at stop-over sites, makes birds an ideal object of homing studies.
Annually, hundreds of millions of small passerines migrate between their breeding grounds in temperate and high latitudes of the Palaearctic and winter quarters in Africa and Asia (Moreau 1972; McClure 1974). Practically everywhere between the Atlantic and the Pacific, the migrants encounter a wide belt with the environment drastically different from the conditions these species are used to in summer and in winter. For woodland passerines from the Central and Eastern Palaearctic, this unfavourable zone includes the belt of steppes, semideserts and deserts, large highlands of Central Asia and mountain deserts. The most difficult situation may arise for passerines from the Eastern Palaearctic which spend their winter in Africa to the south of the equator. In Eastern Siberian populations of Phylloscopus trochilus or Oenanthe oenanthe, the calculated migration distance may reach 10 000 km which is 1.5–2 times longer than in the European populations (Moreau 1972). Finally, both Asian and African migrants may face the necessity to cross the world’s largest highlands in Central Asia, including the Tien Shan, Pamiro-Alay and the Himalayas. The overall length of the migratory route over the ecologically inhospitable areas of western Central Asia alone may reach 3500 km. This is quite comparable with the migratory route over the Atlantic between the Americas (Williams and Williams 1990).
More than 200 years ago, Lazzaro Spallanzani (Accademia d’Italia, 1934) wondered how birds — sand martins in his case — found their way back home after they had been displaced inadvertently to unknown territory, but the first to marvel at the amazing homing abilities of insects was Jean Henri Fabre (1879, 1882). He released some megachilid bees and sphecid wasps up to 4 km away from home and was surprised to find that many of them returned to their nesting sites the very same day. Even though he performed a number of experiments including the attachment of tiny magnets to the homing bees, he finally was left with the conclusion that his experimental animals possessed some enigmatic sense of directionality. Nevertheless he started what can be called the first period of research on homing in insects. In this period, which culminated in the discovery of the insect’s celestial compass (Santschi, 1911, 1923; see Wehner, 1990a), most investigators focused on the sensory basis of insect navigation.
A goal oriented migrant optimizing energy expenditure during flight should coordinate the adaptation of heading and airspeed with respect to wind. The model introduced in this study combines for the first time the simultaneous adaptation of heading and airspeed in an optimal strategy. Compared to other models (constant track or constant airspeed), the largest benefit from using the optimal strategy results with lateral and opposing winds. With decreasing distance to the goal, compensation for wind drift should be extended by adjusting heading and increasing airspeed. Regardless of their flight mechanics, birds completing their migratory journey in a few long flights should fly faster and compensate more for lateral wind drift, than birds travelling in numerous short hops. An analysis of flight paths of small passerines gathered with a tracking radar at night showed good correlations between measured headings and airspeeds and those predicted by the optimal strategy.
Migratory birds occupy geographically and ecologically disparate areas during their annual cycle with conditions on breeding and non-breeding grounds playing separate and important roles in population dynamics. We used data from nuclear microsatellite and mitochondrial DNA control region loci to assess the breeding and non-breeding spatial genetic structure of a transoceanic migrant shorebird, the bristle-thighed curlew. We found spatial variance in the distribution of allelic and haplotypic frequencies between the curlew’s two breeding areas in Alaska but did not observe this spatial structure throughout its non-breeding range on low-lying tropical and subtropical islands in the Central Pacific (Oceania). This suggests that the two breeding populations do not spatially segregate during the non-breeding season. Lack of migratory connectivity is likely attributable to the species’ behavior, as bristle-thighed curlews exhibit differential timing of migration and some individuals move among islands during non-breeding months. Given the detrimental impact of many past and current human activities on island ecosystems, admixture of breeding populations in Oceania may render the bristle-thighed curlew less vulnerable to perturbations there, as neither breeding population will be disproportionally affected by local habitat losses or by stochastic events. Furthermore, lack of migratory connectivity may enable bristle-thighed curlews to respond to changing island ecosystems by altering their non-breeding distribution. However, availability of suitable non-breeding habitat for curlews in Oceania is increasingly limited on both low-lying and high islands by habitat loss, sea level rise, and invasive mammalian predators that pose a threat to flightless and flight-compromised curlews during the molting period.
Reconstruction of breeding habitat of North American Neotropical migrants 18,000 years ago and 9,000 years ago indicated major shifts in both location and composition of plant communities relative to present conditions. Increased vegetation in xeric areas may have compensated, at least in part, for the reduction in breeding habitat due to glaciation. Autumnal flights of Neotropical passerine migrants flying on constant headings from North America to Central and South America were simulated under present wind conditions and for winds during periods of glaciation at 18,000 and 9,000 years ago. The 155 ø average headings currently observed for Atlantic migrants were found to function well during periods of glaciation and may have been more generally useful during those times than at present.
Migrating birds make the longest non‐stop endurance flights in the animal kingdom. Satellite technology is now providing direct evidence on the lengths and durations of these flights and associated staging episodes for individual birds. Using this technology, we compared the migration performance of two subspecies of bar‐tailed godwit Limosa lapponica travelling between non‐breeding grounds in New Zealand (subspecies baueri) and northwest Australia (subspecies menzbieri) and breeding grounds in Alaska and eastern Russia, respectively. Individuals of both subspecies made long, usually non‐stop, flights from non‐breeding grounds to coastal staging grounds in the Yellow Sea region of East Asia (average 10 060 ± SD 290 km for baueri and 5860 ± 240 km for menzbieri). After an average stay of 41.2 ± 4.8 d, baueri flew over the North Pacific Ocean before heading northeast to the Alaskan breeding grounds (6770 ± 800 km). Menzbieri staged for 38.4 ± 2.5 d, and flew over land and sea northeast to high arctic Russia (4170 ± 370 km). The post‐breeding journey for baueri involved several weeks of staging in southwest Alaska followed by non‐stop flights across the Pacific Ocean to New Zealand (11 690 km in a complete track) or stopovers on islands in the southwestern Pacific en route to New Zealand and eastern Australia. By contrast, menzbieri returned to Australia via stopovers in the New Siberian Islands, Russia, and back at the Yellow Sea; birds travelled on average 4510 ± 360 km from Russia to the Yellow Sea, staged there for 40.8 ± 5.6 d, and then flew another 5680–7180 km to Australia (10 820 ± 300 km in total). Overall, the entire migration of the single baueri godwit with a fully completed return track totalled 29 280 km and involved 20 d of major migratory flight over a round‐trip journey of 174 d. The entire migrations of menzbieri averaged 21 940 ± 570 km, including 14 d of major migratory flights out of 154 d total. Godwits of both populations exhibit extreme flight performance, and baueri makes the longest (southbound) and second‐longest (northbound) non‐stop migratory flights documented for any bird. Both subspecies essentially make single stops when moving between non‐breeding and breeding sites in opposite hemispheres. This reinforces the critical importance of the intertidal habitats used by fuelling godwits in Australasia, the Yellow Sea, and Alaska.
Many birds live in environments that undergo marked variation in the course of the day and the year. From day to night the light level can change 1,000,000-fold, and under extreme conditions the air temperature can drop from +30°C to 5°C, or the relative humidity can rise from 20% to 80%. The same kind of variation can apply to the alternation between summer and winter, with months of permanent light followed by months of permanent darkness at the poles, with a temperature range of +30°C to -40°C in a continental climate and a several-meter snow cover that can persist for several winter months in mountain areas or high latitude with high precipitation. Superimposed on these predictable changes in the abiotic environment are unpredictable weather events. The climatic fluctuations are paralleled by changes in the biotic environment of a bird; certain prey animals or food plants disappear temporarily or are periodically not accessible. Birds have a relatively high metabolic rate, which implies continual energy consumption and a constant supply of food. To ensure that this supply is uninterrupted despite the extreme variation in availability of food, birds have developed many strategies, without which they would not have been able to survive in a diversity of habitats.
A migrating bird's response to wind can impact its timing, energy expenditure, and path taken. The extent to which nocturnal migrants select departure nights based on wind (wind selectivity) and compensate for wind drift remains unclear. In this paper, we determine the effect of wind selectivity and partial drift compensation on the probability of successfully arriving at a destination area and on overall migration speed. To do so, we developed an individual-based model (IBM) to simulate full drift and partial compensation migration of juvenile Willow Warblers (Phylloscopus trochilus) along the southwesterly (SW) European migration corridor to the Iberian coast. Various degrees of wind selectivity were tested according to how large a drift angle and transport cost (mechanical energy per unit distance) individuals were willing to tolerate on departure after dusk. In order to assess model results, we used radar measurements of nocturnal migration to estimate the wind selectivity and proportional drift among passerines flying in SW directions. Migration speeds in the IBM were highest for partial compensation populations tolerating at least 25% extra transport cost compared to windless conditions, which allowed more frequent departure opportunities. Drift tolerance affected migration speeds only weakly, whereas arrival probabilities were highest with drift tolerances below 20°. The radar measurements were indicative of low drift tolerance, 25% extra transport cost tolerance and partial compensation. We conclude that along migration corridors with generally nonsupportive winds, juvenile passerines should not strictly select supportive winds but partially compensate for drift to increase their chances for timely and accurate arrival.
We studied flight direction relative to wind direction (hereafter referred to as “flight direction”), the relation between wing morphology and flight behaviour and interspecies relationships in flight behaviour among all major seabird taxa. We calculated wing loading and aspect ratios for 98 species from 1029 specimens. Species were sorted into 13 groups on the basis of similarity in patterns of flight direction. The primary flight direction of Pelecaniformes and Charadriiformes was into and across headwinds. The most common flight direction of Procellariiformes was across wind. Seabirds avoided flying with tailwinds. Wing loading and aspect ratios were positively correlated in Procellariiformes, Pelecaniformes and alcids but negatively correlated in larids. In Procellariiformes, incidence of headwind flight and that of tailwind flight were significantly correlated with wing loading and aspect ratio; species with higher wing loading and aspect ratios flew more often into headwinds and less often with tailwinds. In contrast, the proportion of Pelecaniformes and Charadriiformes flying with tailwinds increased significantly with increased wing loading. Our results demonstrate a close link in seabirds between flight behaviour, wing morphology and natural history patterns in terms of distribution, colony location, dispersal and foraging behaviour.
We documented fat loads and abdominal organ sizes of Bar-tailed Godwits (Litnosa lapponica baueri) that died after colliding against a radar dome on the Alaska Pen-insula, most likely just after takeoff on a trans-Pacific flight of 11,000 km, and of birds of the same subspecies just before northward departure from New Zealand. We compared these data with data on body composition of godwits of the smaller lapponica subspecies obtained during a northward stopover in The Netherlands. As a consequence of high amounts of sub-cutaneous and intraperitoneal fat, and very small fat-free mass, Bar-tailed Godwits from Alaska had relative fat loads that are among the highest ever recorded in birds (ca. 55% of fresh body mass). Compared with northbound godwits from New Zealand, the Alaskan birds had very small gizzards, livers, kidneys, and guts. This suggests that upon departure, long-distance migrants dispense with parts of their "metabolic machinery" that are not di-rectly necessary during flight, and rebuild these organs upon arrival at the migratory des-tination.
We used radio-telemetry to study autumn migratory flight initiation and orientation in relation to wind and air pressure in a nocturnal passerine migrant, the reed warbler Acrocephalus scirpaceus at Falsterbo, southwest Sweden. The majority of the reed warblers departed in the expected migratory direction towards south of southwest, while a low number of the birds took off in reverse directions between north and east. Flight directions at departure correlated with wind directions. These correlations were particularly prominent at higher wind speeds but were absent at wind speeds below 4 m/s. Birds departing in the expected migratory direction compensated completely for wind drift. The reed warblers preferred to depart during nights with tailwinds and when air pressure was increasing suggesting that reed warblers are sensitive to winds and air pressure and select favourable wind conditions for their migratory flights. Since air pressure as well as velocity and direction of the wind are correlated with the passage of cyclones, a combination of these weather variables is presumably important for the birds' decision to migrate and should therefore be considered in optimal migration models.
The study of bird migration by satellite tracking began in the 1980s, after transmitters had become sufficiently small to allow the monitoring of larger migrating species. The initial studies in this direction were all successful with respect to establishing this method (Section 2) of elucidating new migration patterns and various aspects of orientation. These pilot studies are summarized in Section 3, Table 1, Figures 1-4. We believe that studies on avian orientation and navigation will, in general, greatly benefit from satellite tracking if some prerequisites are fulfilled and adequate experiments planned (Section 4). In future studies, smaller transmitters with increased life expectancies are needed, and possible effects of these transmitters on bird behaviour must be examined. Considerable improvement of satellite tracking in avian orientation research is to be expected, along with the development of a new generation of satellites allowing communication between satellites and transmitters (Sections 4, 5).
The general basis of migratory orientation in birds is most probably an endogenous time-and-direction programme. Directions are selected with respect to celestial as well as geomagnetic clues. These clues appear to be integrated within a system that profits from the special advantages of either kind of environmental signal, and thereby can cope with their limitations. Using these clues, and following a genetically determined intended direction (or sequence of directions) over a genetically determined period of time, a bird may reach a larger population-specific area. However, it will hardly be able to find a particular location, such as, for instance, its previous breeding site. Homing to a familiar site over several hundred kilometers of unfamiliar terrain is substantially based on the smelling of atmospheric trace compounds. At shorter distances from home, orientation by means of--presumably visual--familiar landmarks completes the repertoire of mechanisms guiding a bird back home. These mechanisms are considered to be based on different kinds of 'maps' and 'compasses'. Conceptual approaches to the properties of an 'olfactory map' have as yet only reached an early state of speculation.
Polish white storks migrate through the Carpathians or keep away from them, through the Bosphorus, eastern side of the Mediterranean, Sinai and the Nile river, omitting its delta. They winter mainly in Africa, south of 15oN. No differences have been noticed in distribution of wintering places of young storks and adults. Young storks begin and finish autumn migration earlier, and spring migration later than adults. Storks in their 1st and 2nd years of life often do not return to Poland, and stop for summer in the winter quarters, on migration route or off it, mainly in the Nile delta.-from English summary
South African wintering birds migrate via the W seaboards of Africa and Europe. Siberian knots seem to use only a few staging sites between W Africa and Siberia. Most birds only use the W German Wadden Sea. Staging areas of lesser importance are the Tejo Estuary in Portugal, the Vendee coast in France and probably the Westerschelde in SW Netherlands. At the latter 3 sites in early May, birds appear to arrive with lower body weights than in Schleswig-Holstein (W Germany) at the same time. The migration from W Germany to central Siberia is most probably made in one flight via the Gulf of Finland. A model of body weight changes during migration in a fixed time schedule is employed to discuss the energetic constraints on the migration strategy of Siberian knots. -from Authors
Describes the area and presents data on the numbers of waders wintering and the percentage this represents of the East Atlantic flyway. Describes research carried out in the area on food resources for waders and wader foraging.-from Authors
This paper lists a total of 279 bird and 44 mammal species from Micronesia through December 2003, with listings provided for nine island groups or islands, including Palau, Yap, Guam, the Commonwealth of the Northern Mariana Islands, Chuuk, Pohnpei, Kosrae, the Marshall Islands, and Wake Atoll. The region’s avifauna currently comprises 167 visiting species, 81 native breeding species, 13 introduced breeding species, four extinct species, one species extinct in the wild, and 13 hypothetical species. Its mammal fauna contains 18 visiting species, eight native breeding species, 14 introduced breeding species, two extinct species, and two hypothetical species. Species counts are highest for birds at Palau (148 species), the CNMI (144), and Guam (128), and for mammals at Guam (25), Palau (19), and the CNMI (19). These numbers reflect both the closer proximity of these islands to eastern Asia, New Guinea, and the East Asian-Australasian Flyway, and the greater number of observers present. Thirty-eight new bird species have been reported for Micronesia since the last region-wide checklist was published in 1985, whereas the mammal list is the first ever compiled for the region. Species entries in the checklist are annotated with information on status and a documenting reference that is often the first published record. Additional background information on occurrence or taxonomy is given for some species.
ANY passerine birds make long overwater flights during the course of their seasonal migrations; it is obvio8us that natural selection has fa- vored these flights in spite of the risks and energetic demands involved. The Gulf of Mexico is one region where the arrival and departure of overwater migrations can be observed to advantage. Even at the height of the exchange between Lowery (1945) and Williams (1945) concerning the occurrence of spring trans-Gulf migration, it was gen- erally assumed that autumn migrants regularly cross the Gulf in large num- bers (e.g., Williams, 1947). In the years following the controversy, spring migration in the Gulf region has been extensively studied, but there have been few concentrated investigations of fall migration. More or less anecdotal ob- servations of birds crossing the Gulf in fall were made by Griscom (1945), Paynter (1951, 1953) and Siebenaler (1954). Buskirk (1968) studied the arrival of migrants on the north coast of Yucatan. The extensive investigations of vernal trans-Gulf migration have shown that the pattern of air flow around the Bermuda high-pressure system char- acteristic of that season is conducive to overwater flights (Lowery, 1951; Gauthreaux, 1971). Indeed, Gauthreaux has shown that trans-Gulf migra- tions early in spring, when the Bermuda high is not a consistent feature, occur in spurts which are dependent upon the establishment of southerly air flow over the Gulf. After the beginning of April, moist tropical air moves north- ward across the Gulf, interrupted only by the infrequent penetration of power- ful cold fronts. The consistency of this favorable flow pattern has probably been a strong selective force in the evolution of vernal trans-Gulf migration. If this is true, one would predict the development of a different pattern in fall because wind patterns are not favorable for regular, large-scale Gulf crossings. During the fall of 1969 I obtained data on the direction and magnitude of bird flow in southwestern Louisiana while I was conducting field studies on the orientation of nocturnal migrants. These observations shed light on three questions: What is the general flow pattern of autumn migration on the northwestern Gulf coast?; How is this pattern related to major weather sys- tems? ; and What evolutionary strategy has led to the broad-front migration patterns we see today? 231
Two hypotheses for the orientation of autumnal migration over the western North Atlantic Ocean, proposed by Williams and Richardson, were tested by simulating the flight of birds from North to South America through calculated wind fields in the western North Atlantic Ocean. Use of a constant compass heading proved to be a tenable strategy for birds departing from the North American coast as far north as Nova Scotia. The range of successful headings, however, became increasingly restricted at northern latitudes. Airspeed, heading, altitude, and point of departure all had major effects on migratory success. Time required for successful non-stop migration was found to lie between 70 and 100 h for passerines and 40 to 60 h for shorebirds.
Several species of shorebirds migrate between eastern Asia and the southern Pacific islands, Australia, and New Zealand. Observations made from Guam (13°25′N, 144°45′E) during autumn 1983 indicate that a significant number of birds take a direct route over the western Pacific Ocean. Radar observations and ground counts of migrants on Guam showed two periods of autumnal migratory activity. The first, largely adult birds, was in August and September. The second, largely juveniles, was in late September and October. Radar indicated that large numbers of birds passed over the island to the south with no evidence of compensation for drift by the easterly winds. Comparison of radar and ground observations on Guam showed that only a small subset of migrants stop on the island, suggesting that some species may make nonstop flights between eastern Asia and the South Pacific.
This paper reports on recoveries of waders (Charadrii) banded in Australia and recovered in China. From 1953 to 1982, twenty waders and ten species were recovered. Several northward migration routes are depicted. Coastal areas of southeast China are the most important feeding areas for waders migrating from Australia north to the Palearctic. Opportunities exist for strengthening the study of international bird migration between China and Australia. /// 本文首次报道鸻鹬类候鸟, 根据环绕在中国和澳大利亚以外地区回收情况, 分析鸻鹬类迁徙的时间, 地点, 路线和特点. 它们的北迁路线和南迁路线不同, 而且, 中国东南沿海回收环境地点, 是鸻鹬类从澳大利亚北返古北界的重要取食地点; 每年的间隔从 2 个 月 至 4 个 月 不 等; 在中国的迁徙路线, 沿广东, 福建, 浙江和江苏沿海地区北上, 与此同时, 沿海迁徙时亦有分路, 或者沿海岸飞行, 或由长江口分路到朝鲜, 日本北上, 或由山东越过庙岛群岛至东北各省北上; 另一条路线, 由澳大利亚经菲律宾, 至中国河北, 沿海直达黑龙江, 再至西伯利亚. 此外, 文中还提出加强鸟类环境和国际间交流与合作的建议.
This is the first field guide to the identification of the birds of the islands of the tropical Pacific, including the Hawaiian Islands, Fiji, Samoa, Tonga, southeastern Polynesia, and Micronesia. It is intended both as a reference for the expert and as an introduction to birding in the region for the novice. Small enough to be carried afield, it contains much previously unpublished information about behavior, vocalizations, ecology, and distribution. The forty-five color plates depict all plumages of all bird species that breed in the islands, as well as of those that regularly visit them and the surrounding oceans, and of most species believed to be extinct on the islands. Black-and-white figures show many of the rarer visitors.Introductory sections discuss the tropical Pacific as an environment for birds, problems of birding on islands, and bird conservation. Appendixes include maps of the island groups and a thorough bibliography.
The most probable species to carry out a transglacial E/SE-migration in spring are Gavia immer, Clangula hyemalis, Mergus serrator, Anas platyrhynchos and, possibly, Alle alle and Larus hyperboreus. Species involved in the transglacial W/NW-migration comprise geese, Anser albifrons and Branta bernicla, and high arctic waders, Charadrius hiaticula, Arenaria interpres, Calidris canutus and Calidris alba. In addition, it is highly probable that also Oenanthe oenanthe, Sterna paradisaea and Phalaropus lobatus belong to this category.-from Authors
Observations from a network of radars on ships and on islands in the western North Atlantic Ocean and on the eastern coast of North America suggest that successful autumnal migrants moving between North and South America utilize simple compass orientation and do not require bicoordinate navigation. Successful migrants maintained a southeast heading from the North American coast to the Caribbean, Unsuccessful migrants became disoriented over the Atlantic. Visual observations suggest that successful migratory behavior is restricted to certain taxonomic groups of passerines.
Annual cyclicity of body components in wintering Pacific Golden-Plovers (Pluvialis fulva), combined with ecological and behavioral features were variously studied from 1978 through 1987. The primary research site was in Hawaii at the Bellows Air Force Station (BAFS), Oahu. After fall arrival, body weights trended downward for several weeks, possibly in response to the energy required for the behaviors associated with establishing (and reestablishing) residency combined with molting. Major premigratory weight gains began in late March about 1 month prior to migration. Statistical correlations between body weight and fat content are described. Premigratory dehydration as an adaptation to increase flight range and/or energy stores at the migratory destination was likely. Fat-free dry weights (FFDW) at BAFS were least in the fall and greatest in the spring. For juveniles, this difference relates to overall body growth during the first wintering season. With older birds, it may reflect the environmental conditions at the respective end points of migration--predictably favorable for southbound migrants, unpredictable for northbound birds. Plovers wintering on Enewetak Atoll and Wake Island had significantly higher FFDWs than the birds at BAFS. Possible factors in this relationship are discussed. The BAFS population contained many territorial birds, and showed high rates of survival and site fidelity over successive years. Juveniles arriving on the wintering grounds for the first time probably experience considerable mortality as they compete with established adults for space and resources. Based on wing lengths, many of the plovers involved in this study were from Alaska breeding grounds. Flyways to the tundra may involve staging areas, but specific information is lacking. Using current formulae, we describe the relationship between body weight and flight range, and provide estimates of the fat required to reach various landfalls.
Relationships of short-term weather to daily migration intensity are reviewed, with sections for each weather variable, for waterfowl, shorebirds and hawks, and for reverse migration. Selecting factors, methodology, hypotheses and results to date are summarized, generalizations about migration-weather relationships are extracted from the pooled results, and high-priority research topics are identified. Ultimate factors responsible for present responses are thought to include aspects of weather en route and a the take-off point and destination. Proximate factors affecting the probability of take-off may include variables useful in predicting, as well as those that measure, aspects of weather with selective significance. Causative and coincidental relationships remain difficult to separate, and at least a few birds migrate in almost any weather conditions. However, maximum numbers migrate with fair weather, with tailwinds and with temperature, pressure and humidity conditions that accompany tailwinds. Correlations with weather differ among populations with different flight directions. General patterns of responses appear to be modified by special selecting factors that apply to certain groups - soaring hawks tend to fly on days with strong updrafts, landbirds migrating along coasts prefer onshore to offshore winds, and transients in unsuitable habitats seem less likely to wait for favourable travelling conditions. /// дан обзор взаимосвязи погодных усповий и иитенсивности суточных миграпий с раздепами, посвященными анализу впияния отдельных погодных факторов на миграции водоплавающих, береговых и хищных птиц и на обратные мнграции. Обобщены сепеютирукщие факторы, методопогия, гипотезы и результаты, имеющиеся в настоящее время, сдепаны выводы о взаимосвязях миграции-погода, на основании имеющихся материапов определены генералвные направюения иччледований. Предполагается, что ультимативные фактопы, определяющие эти отношения, включают характер погоды по маршруту миграции, а также в точках отлета и назначения. Непосредственное влияние на отлет могут оказывать различные аспекты погоды, которые можно измерить ипи предсказать: отдельные факторы имеюь различную значимость. Причинные и сопутсвующие связи трудно разделить и, по крайней мере, некоторые птицы мигрируют при погодных условиях. Однако, максимальное количество птиц мигрирует при хорошей погоде, попутном ветре и соответствующих температурах, атмосферном давлении и влажности. Основной характер взаимосвязей может модифицироваться специальными фактояами, которые имеюь значение для некоторых хищников, парящих группами и предпочитающих дни с сильными вертикальными токами, а также у сухопутных птиц, мигрирующих вдопь берега и предпочитающих ветер с моря береговому бризу, и наконец, у перелетных птиц, оказывающихчя на пролете в неподходящих местообитаниях, которые не дожидаются наиболее благоприятных условий для перелета.
Knots occurring in north Norway in spring have been presumed to breed in Siberia. We find that, based on their body size, ringing locations and migration timing, Knots in Balsfjord, north Norway, in May belong to the Nearctic breeding population C. c. islandica. Some moult in autumn on the Wash and Wadden Sea, and overwinter in Britain, notably at Teesmouth and the Wash. Some may reach Balsfjord in May after a direct flight from the Wash. 15 000-28 000 Knots are present for 2-3 wk in May, departing between 25-30 May, making Balsfjord a staging site of major international importance to Knots. The breeding origins of at least 30 000 Knots present in Porsangerfjord (250 km NE) are unknown, but migration timing and ringing location indicates possible Nearctic origin for these also.
A network of nine radar sites was used to estimate the flight time of autumnal migrants crossing the western North Atlantic Ocean between the northeastern North American coast and Bermuda and Antigua, West Indies. Arrival of large numbers of birds at Bermuda showed a significant increase during the day with a peak of 1600 G.M.T.; if this peak corresponds to the sharp onset of departures after sunset recorded at North American coastal sites, a flight time of approximately 18 hours between the coast and Bermuda is indicated. Arrival at Antigua of large numbers of birds from the north and northeast showed a gradual increase during the day. Observations at North American coastal radars indicated that departures were most likely to be moderate or heavy 64-70 hours before significant numbers of birds were detected at Antigua. After passing over Antigua, the birds presumably arrived at the northern coast of South America about 18 hours later.
Although radar screens are frequently covered with bird echoes during migration periods, estimating bird densities from the displayed echoes is difficult. Weather radars have attenuation circuits that are used to measure the intensity of rain storms, and these devices can be employed to determine the number of migrating birds aloft at night and during the day. The types of birds responsible for the echoes can be identified by simultaneous telescopic observations, and these observations can also be used to calibrate the radar displays.
THE opportunity to record bird movements with radar has undoubtedly
existed in the Far East, but we know of no published studies of bird
migration that utilized radar in Indonesia, Malaysia, Thailand, Vietnam,
the Philippine Islands, Taiwan, American Micronesia or even Japan. We
report here a radar study of bird migration over Hong Kong (which lies
between 22° 9' and 22° 37' N and 113° 52' and 114° 30'
E) to stimulate the use of radar to study bird migrations across or
between some of the countries mentioned, and also additional studies on
the mainland of China.
Radars, systematic visual observations from the coast, and aerial surveys were used to study migration near the Yukon (1975) and Alaskan (1977-78) coasts of the Beaufort Sea. Conspicuous eastward migration of loons, brant, seaducks, jaegers and glaucous gulls occurs along the icebound coast, and in the Yukon some eastbound species (especially brant) concentrate coastally. Overall, however, eastward migration is predominantly broad-front with little coastal concentration. Most eiders and perhaps most oldsquaws, the commonest waterbirds, fly east offshore where there is more open water. Westward migration is much less conspicuous visually; swans, geese and pintails are the main groups seen. However, radar shows extensive broad-front westward flights, probably largely of shorebirds. Most spring migration, both east and west, is from 15 May to 20 June, with the coastal peak (25 May-15 June) apparently being later than that offshore. Some coastal migrants land on river water that overtlows onto nearshore ice in early June. Some waterbirds bypass the largely ice-covered Alaskan Beaufort by flying northeast across interior Alaska and/or northwestern Canada from the Pacific Ocean to the Canadian Arctic. These overland migrants include some yellow-billed and arctic loons, brant and jaegers; probably most Thayer's gulls; and probably some oldsquaws, Sabine's gulls, arctic terns and other species.
Westward moult migrations of seaducks were studied in the summers of 1972 and 1975 (northern Yukon) and 1977-78 (west of Prudhoe Bay, Alaska). Methods used were visual observations from the coast, aerial surveys, and (in 1975) DEW radar. Many male Oldsquaws (Clangula hyemalis) fly west near the north coast of Alaska in early July. Most seem to travel only a short distance; tens of thousands subsequently moult in various lagoons along northern Alaska. Few of the male eiders (Somareria spp.) that leave the Beaufort Sea in summer travel west along the coast past the two study areas. Instead, the main route may be seaward of the barrier islands until the eiders approach Point Barrow. In late June and July, several thousand male Surf Scoters (Melanitta perspicillata) fly west near the Yukon and Alaskan coast to moulting areas in lagoons. This flight, unlike moult migrations of most scoters, is not directed toward the wintering areas.
There were 82 families of birds represented in this study. The average number of birds ringed per family was 14,197 and per species was 954; however, 19 families accounted for 92.1% of the ringed birds. Among these there were 15 species which made up 59.6% of the total and of these the House Swallow Hirundo rustica made up 24.2%. Forty-four of the families had less than 1500 birds marked per family, totaling only one percent of the birds ringed. The remaining 38 families averaged 30,340 birds per family. The average among the 15 highest species was 46,000. Without the House Swallow the average per species was 29,000. The remaining 1201 species averaged only 389 birds marked per species. When the 19 high families are deducted from the total, the remaining 63 families averaged only 1458 birds per family. (Modified author abstract)