Migratory Flyways Research Articles

Dispersal of North American Polymorphidae (Acanthocephala) and aquatic birds (Anatidae and Rallidae) along the Central Migratory Flyway

Dispersal of North American Polymorphidae (Acanthocephala) and aquatic birds (Anatidae and Rallidae) along the Central Migratory Flyway

Migration strategy, site fidelity and population size of the globally threatened Sociable Lapwing Vanellus gregarius

Population declines of the critically endangered Sociable Lapwing are probably due to high mortality along its migration routes or on its wintering grounds, both of which are very poorly known. We therefore undertook a long-term study of the species’ movements using satellite tagging, colour-ringing, targeted field surveys and a database of historical and recent sightings. We identified two migration flyways from the breeding grounds in Kazakhstan; a longer western route (c. 5200 km) west through southern Russia, then south through the Caucasus to wintering areas in Saudi Arabia and eastern Sudan, and a shorter eastern route (c. 2800 km) south through Turkmenistan and Uzbekistan to wintering areas in Pakistan and north-western India. The migration strategy is characterised by infrequent long-distance movements followed by often lengthy stopovers in a small number of staging areas that are used consistently across years, and by high individual and low between-individual consistency in spatial and temporal patterns of movement. At least four main autumn stopover areas and one additional spring stopover area were identified along the western route, but only one autumn and one spring staging area along the eastern route. There was no relationship between latitude or longitude of breeding and the migration route used, and the same breeding colonies could contain breeding adults and produce chicks of both flyway populations, suggesting that no clear migratory divide exists within the breeding range. Sociable Lapwings spend around a third of the year on their breeding grounds, a third on their wintering grounds and a third moving between them. Birds were highly faithful to passage and wintering sites, but showed low fidelity to breeding sites. Stopover areas and wintering sites are usually located at the interface of dry steppe-like or desert habitats and agriculture, particularly irrigated cropland along rivers. This species selects agricultural habitats throughout its entire life cycle, and its heavy reliance on some of the world’s most anciently cultivated regions suggests that this synanthropic relationship may have evolved over millennia. The recent emergence of irrigated agriculture in the deserts of Arabia allows birds using the western route to winter far north of their previous wintering range and maybe to spread into new wintering areas along the coasts of the Arabian Gulf. The concentration of large numbers of birds at a small number of traditional stopover areas offers the opportunity to quantify the global population size, which we estimate at around 24,000 individuals (95% CL 13,700–55,560). However, it also makes the species particularly vulnerable to hunting and small-scale habitat change. Illegal hunting along the western flyway is identified as the most likely driver of the species’ decline.

Sex, age, molt strategy, and migration distance explain the phenology of songbirds at a stopover along the East Asian flyway

Sex- and age-specific differences in the timing of migration are widespread among animals. In birds, common patterns are protandry, the earlier arrival of males in spring, and age-differential migration during autumn. However, knowledge of these differences stems mainly from the Palearctic-African and Nearctic-Neotropical flyways, while detailed information about the phenology of migrant birds from the East Asian flyway is far scarcer. To help fill parts of this gap, we analyzed how migration distance, sex, age, and molt strategy affect the spring and autumn phenologies of 36 migrant songbirds (altogether 18,427 individuals) at a stopover site in the Russian Far East. Sex-differential migration was more pronounced in spring than in autumn, with half of the studied species (6 out of 12) showing a protandrous migration pattern. Age-differences in migration were rare in spring but found in nearly half of the studied species (11 out of 25) in autumn. These age effects were associated with the birds’ molt strategy and the mean latitudinal distances from the assumed breeding area to the study site. Adults performing a complete molt before the onset of autumn migration passed the study site later than first-year birds undergoing only a partial molt. This pattern, however, reversed with increasing migration distance to the study site. These sex-, age-, and molt-specific migration patterns agree with those found along other flyways and seem to be common features of land bird migration strategies.Significance statementThe timing of animal migration is shaped by the availability of resources and the organization of annual cycles. In migrant birds, sex- and age-differential migration is a common phenomenon. For the rarely studied East Asian flyway, we show for the first time and based on a large set of migrant songbirds that earlier migration of males is a common pattern there in spring. Further, the timing and extent of molt explained age-differential migration during autumn. Adults molting their complete plumage at the breeding area before migration showed delayed phenology in comparison to first-year birds, which perform only a partial molt. This pattern, however, reversed with increasing migration distance to the study site. Since our results agree with the general patterns from the other migration flyways, similar drivers for differential migration may act across different flyway systems, provoking a similar evolutionary response.

RECORDING OF THE SPRING MIGRATION OF SOARING BIRDS THROUGH GEBEL EL ZEIT, EASTERN DESERT, EGYPT

Egypt is an important pass for the soaring birds’ migration, as it is situated on the mainland connection between the Eurasian and African landmasses that connects breeding grounds in Eurasia with wintering zones in Africa. In the current study, the spring migration of soaring birds was studied along a narrow corridor “bottleneck site” located within the Red Sea/Rift Valley bird migration flyway, Gulf of Suez, Egypt. Over a period of four weeks from April 19th to 17th of May 2019, 89949 soaring birds of 27 species were counted during an eight-hour daily observation window. In total, 47511 raptors of 24 species were recorded. The most common were the group of Levant sparrowhawk “Accipter brevipes”, European honey buzzard “Pernis apivorus”, and Northern steppe buzzard “Buteo buteo vulpinus” forming 33.16%, 32.08%, and 24.91% of all raptors, respectively; while combined black kite “Milvus migrans”, lesser spotted eagle “Aquila pomarine”, steppe eagle “Aquila nipalensis”, short-toed eagle “Circaetus gallicus”, booted eagle “Aquila pennata”, and Egyptian vulture “Neophron percnopterus” recorded more than 6% of the raptor assemblage. In addition, 15 greater spotted eagle “Aquila clanga”, 6 pallid harrier “Circus macrourus”, and 5 Eurasian griffon vulture “Gyps fulvus” were recorded during the observations. Other soaring birds were recorded during the study-time, the most common were: 36700 white stork “Ciconia Ciconia”, 4230 great white pelican “Pelecanus onocrotalus”, and 1500 black stork “Ciconia nigra”.

RECORDING OF THE SPRING MIGRATION OF SOARING BIRDS THROUGH GEBEL EL ZEIT, EASTERN DESERT, EGYPT

Egypt is an important pass for the soaring birds’ migration, as it is situated on the mainland connection between the Eurasian and African landmasses that connects breeding grounds in Eurasia with wintering zones in Africa. In the current study, the spring migration of soaring birds was studied along a narrow corridor “bottleneck site” located within the Red Sea/Rift Valley bird migration flyway, Gulf of Suez, Egypt. Over a period of four weeks from April 19th to 17th of May 2019, 89949 soaring birds of 27 species were counted during an eight-hour daily observation window. In total, 47511 raptors of 24 species were recorded. The most common were the group of Levant sparrowhawk “Accipter brevipes”, European honey buzzard “Pernis apivorus”, and Northern steppe buzzard “Buteo buteo vulpinus” forming 33.16%, 32.08%, and 24.91% of all raptors, respectively; while combined black kite “Milvus migrans”, lesser spotted eagle “Aquila pomarine”, steppe eagle “Aquila nipalensis”, short-toed eagle “Circaetus gallicus”, booted eagle “Aquila pennata”, and Egyptian vulture “Neophron percnopterus” recorded more than 6% of the raptor assemblage. In addition, 15 greater spotted eagle “Aquila clanga”, 6 pallid harrier “Circus macrourus”, and 5 Eurasian griffon vulture “Gyps fulvus” were recorded during the observations. Other soaring birds were recorded during the study-time, the most common were: 36700 white stork “Ciconia Ciconia”, 4230 great white pelican “Pelecanus onocrotalus”, and 1500 black stork “Ciconia nigra”.

Using oxygen and hydrogen stable isotopes to track the migratory movement of Sharp-shinned Hawks (Accipiter striatus) along Western Flyways of North America.

The large-scale patterns of movement for the Sharp-shinned Hawk (Accipiter striatus), a small forest hawk found throughout western North America, are largely unknown. However, based on field observations we set out to test the hypothesis that juvenile migratory A. striatus caught along two distinct migration routes on opposite sides of the Sierra Nevada Mountains of North America (Pacific Coast and Intermountain Migratory Flyways) come from geographically different natal populations. We applied stable isotope analysis of hydrogen (H) and oxygen (O) of feathers, and large scale models of spatial isotopic variation (isoscapes) to formulate spatially explicit predictions of the origin of the migrant birds. Novel relationships were assessed between the measured hydrogen and oxygen isotope values of feathers from A. striatus museum specimens of known origin and the isoscape modeled hydrogen and oxygen isotope values of precipitation at those known locations. We used these relationships to predict the origin regions for birds migrating along the two flyways from the measured isotope values of migrant’s feathers and the associated hydrogen and oxygen isotopic composition of precipitation where these feathers were formed. The birds from the two migration routes had overlap in their natal/breeding origins and did not differentiate into fully separate migratory populations, with birds from the Pacific Coast Migratory Flyway showing broader natal geographic origins than those from the Intermountain Flyway. The methodology based on oxygen isotopes had, in general, less predictive power than the one based on hydrogen. There was broad agreement between the two isotope approaches in the geographic assignment of the origins of birds migrating along the Pacific Coast Flyway, but not for those migrating along the Intermountain Migratory Flyway. These results are discussed in terms of their implications for conservation efforts of A. striatus in western North America, and the use of combined hydrogen and oxygen stable isotope analysis to track the movement of birds of prey on continental scales.

Epidemiological hypothesis testing using a phylogeographic and phylodynamic framework

Computational analyses of pathogen genomes are increasingly used to unravel the dispersal history and transmission dynamics of epidemics. Here, we show how to go beyond historical reconstructions and use spatially-explicit phylogeographic and phylodynamic approaches to formally test epidemiological hypotheses. We illustrate our approach by focusing on the West Nile virus (WNV) spread in North America that has substantially impacted public, veterinary, and wildlife health. We apply an analytical workflow to a comprehensive WNV genome collection to test the impact of environmental factors on the dispersal of viral lineages and on viral population genetic diversity through time. We find that WNV lineages tend to disperse faster in areas with higher temperatures and we identify temporal variation in temperature as a main predictor of viral genetic diversity through time. By contrasting inference with simulation, we find no evidence for viral lineages to preferentially circulate within the same migratory bird flyway, suggesting a substantial role for non-migratory birds or mosquito dispersal along the longitudinal gradient.

Population‐specific adjustment of the annual cycle in a super‐swift trans‐Saharan migrant

For migratory birds optimal timing of the onset of reproduction is vital, especially when suitable conditions for reproduction occur only for a short while during the year. With increasing latitude the suitable period becomes shorter and we expect the organization of annual cycle to be more synchronized to the local conditions across individuals of same population. This should result in low variation of arrival and departure date in breeding sites at higher latitudes. We quantify the temporal and geographical variation in pre‐ and post‐breeding migration between individuals from four different populations of alpine swifts Tachymarptis melba along a latitudinal gradient. We tracked 215 individuals in three years with geolocators. The two western and two eastern populations showed separate migratory flyways and places of residence in Africa. Length of stay at the breeding sites was negatively correlated with latitude and differed by more than a month between populations. Duration of migration was similarly short in all populations (median 6.2 days in autumn and 8.7 days in spring). However, variation in timing of migration was unrelated to latitude and individuals everywhere arrived in the same asynchrony at the breeding site.

Earlier and slower or later and faster: Spring migration pace linked to departure time in a Neotropical migrant songbird.

Migratory birds travel vast distances and the timing of migratory flights can affect survival and the ability to reproduce. For Neotropical migrant songbirds, early spring departure from wintering sites, early arrival to the breeding grounds and higher reproductive success have been related to the use of suitable habitats and environmental conditions during the non-breeding season. However, how migratory strategies are shaped by winter habitat choice is largely unknown due to the general inability to track birds from specific wintering habitats to stopovers or breeding destinations. We assessed how winter habitat (native forest vs. shade-grown coffee plantations) relates to spring departure date and migration pace in Swainson's Thrush Catharus ustulatus. We also determined the effect of departure date and total migration duration on the arrival date of birds detected near or within their breeding range. We used a novel application of Motus radiotelemetry arrays to track individuals from their wintering grounds in the Andes of South America along their migratory journey to North America. We found variation in migratory strategies between habitats, with birds wintering in native forest departing later than birds in coffee. We present isotopic evidence for native forest being of higher quality than shade-coffee for Swainson's Thrush and hypothesize that moister conditions in forest, as shown by stable isotope (δ13 C) analysis of thrush whole blood, provides favourable pre-migratory conditions allowing birds to delay departure from wintering grounds. Habitat, between-site and -year variation in departure date, suggests that birds made facultative adjustments to winter habitat quality and environmental conditions. Independent of habitat, birds that departed later migrated faster and this pattern was maintained along the migration route (n=44). Migrating earlier and slower or later and faster was unlikely to result in significant differences in arrival time to breeding destinations. Our findings reveal underappreciated complexity in migratory decisions by long-distance migrants that contrast with the current paradigm of earlier departures and arrival from optimal habitats. The next step is to understand the relative fitness benefits of early versus late schedules or whether each strategy is an equally good response to experienced conditions.

Phylogeny of Hungarian EBLV-1 strains using whole-genome sequence data.

European bat lyssavirus 1 (EBLV-1) is a widespread lyssavirus across Europe, whose epizootic cycle is linked to a few bat species. Occasionally, EBLV-1 infection may occur in domestic animals and humans. EBLV-1 can be classified into two subtypes, where subtype EBLV-1a shows a wide geographic distribution between France and Russia whereas subtype EBLV-1b is distributed between Spain and Poland. In this study, we determined the genome sequence of two recent EBLV-1a strains detected in Hungary and analysed their adaptive evolution and phylodynamics. The data set that included 100 EBLV-1 genome sequences identified positive selection at selected sites in genes coding for viral proteins (N, codon 18; P, 141 and 155; G, 244 and 488; L, 168, 980, 1597 and 1754). A major genetic clade containing EBLV-1a isolates from Hungary, Slovakia, Denmark and Poland was estimated to have diverged during the 19th century whereas the divergence of the most recent ancestor of Hungarian and Slovakian isolates dates back to 1950 (time span, 1930 to 1970). Phylogeographic analysis of the EBLV-1a genomic sequences demonstrated strong evidence of viral dispersal from Poland to Hungary. This new information indicates that additional migratory flyways may help the virus spread, a finding that supplements the general theory on a west-to-east dispersal of EBLV-1a strains. Long-distance migrant bats may mediate the dispersal of EBLV-1 strains across Europe; however, structured surveillance and extended genome sequencing would be needed to better understand the epizootiology of EBLV-1 infections in Europe.

Genetic diversity, phylogeography, and evolutionary dynamics of highly pathogenic avian influenza A (H5N6) viruses.

From 2013 onwards, the spread of novel H5N6 highly pathogenic avian influenza (HPAI) viruses in China has posed great threats to not only poultry industry but also human health. Since late-2016 in particular, frequent outbreaks of clade 2.3.4.4 H5N6 HPAI viruses among wild birds have promoted viral dissemination in South Korea, Japan, and European countries. In response to those trends, we conducted molecular genetic analysis of global clade 2.3.4.4 H5N6 viruses in order to characterize spatio-temporal patterns of viral diffusion and genetic diversity among wild birds and poultry. The clade 2.3.4.4 H5N6 viruses were classified into three groups (Group B, C, and D). During the cocirculation of Group C/D H5N6 viruses from 2013 to 2017, viral movements occurred between close or adjacent regions of China, Vietnam, South Korea, and Japan. In addition, viral migration rates from Guangdong and Hunan to multiple adjacent provinces seemed to have been highly supported by transmission routes (Bayes factors >100), suggesting that southern China was an epicenter for the spread of H5N6 viruses in poultry during that period. Since the introduction of H5N6 viruses originating in wild birds in late-2016, evolving H5N6 viruses have lost most previous genotypes (e.g. G1, G2, and G1.2), whereas some prevailing genotypes (e.g. G1.1, G1.1.b, and G3) in aquatic birds have been dominated, and in particular, the effective population size of H5N6 originating in wild birds dramatically increased; however, the population size of poultry-origin H5N6 viruses declined during the same period, indicating that wild bird migration might accelerate the genetic diversity of H5N6 viruses. Phylogeographic approaches revealed that two independent paths of H5N6 viruses into South Korea and Japan from 2016 to 2018 and provided evidence of Group B and Group C H5N6 viruses were originated from Europe and China, respectively, as regions located in the East Asia–Australian migration flyway, which accelerated the genetic variability and dissemination. Altogether, our study provides insights to examine time of origin, evolutionary rate, diversification patterns, and phylogeographical approach of global clade 2.3.4.4 H5N6 HPAI viruses for assessing their evolutionary process and dissemination pathways.

Including ecosystem descriptors in current fishery data collection programmes to advance towards a holistic monitoring: Seabird abundance attending demersal trawlers

To develop an ecosystem-based approach to fisheries management a holistic perspective is necessary that goes beyond target species management to preserve ecosystem functioning and, therefore, secure future food availability. To achieve these objectives, current fishery data collection programmes should widen their objectives to include the collection of ecosystem descriptors to effectively take advantage of funding and human resources in relation to fisheries monitoring already in place. From an ecological perspective, fishing discards are food subsidies unnaturally available that can profoundly impact the life history traits and population dynamics of seabirds, as well as community structure. In 2015, we took advantage of the Data Collection Framework (DCF) programme, monitoring the Basque trawling fleet, to monitor seabird abundance associated with trawlers as an additional task to be performed by the observers. The main objectives were (1) to develop a standard protocol from an interdisciplinary expert committee, (2) to obtain baseline information of seabird association with trawlers to be able to track changes and (3) to understand seabird abundance in relation to discard facilitation processes based on environmental and fishing parameters. Based on the developed standard protocol, more than 21 species of seabirds were recorded in 241 fishing hauls in the Bay of Biscay (ICES areas 8abd). This biogeographic area is an important migratory flyway and wintering area, where maximum number of seabirds attending trawlers were recorded between December and April (2015–2019). Based on Generalised Linear Models, seabird abundance was higher in multiple situations: harsher environmental conditions, less available discards, shallower areas, increased period of discard availability, higher number of trawlers simultaneously operating in the same fishing ground, in addition to the months of February and April. The core discarding ground was located in the outer French shelf between the latitudinal range of 44.5°N and 46°N, especially for otter trawl fishing. Our approach puts into value the seabird counts that the observers of the DCF can perform systematically, collecting relevant information on the effect of trawling on other biodiversity components such as seabirds. This information will be critical to respond to the application of the reform of the Common Fisheries Policy regarding the effect of the Landing Obligation that seeks fishing sustainability.

Subtype Diversity of Influenza A Virus in North American Waterfowl: a Multidecade Study.

The discovery in 1976 of waterfowl as the primary reservoir of influenza A viruses (IAVs) has since spurred decades of waterfowl surveillance efforts by researchers dedicated to understanding the ecology of IAV and its subsequent threat to human and animal health. Here, we employed a multidecade, continental-scale approach of surveillance data to understand trends of seasonal IAV subtype diversity. Between 1976 and 2015, IAVs were detected in 8,427 (10.8%) of 77,969 samples from migratory waterfowl throughout the Central and Mississippi Migratory Flyways in the United States and Canada. A total of 96 hemagglutinin (HA)/neuraminidase (NA) subtype combinations were isolated, which included most HA (H1 to H14) and all 9 NA subtypes. We observed an annual trend of high influenza prevalence, involving a few dominant subtypes, on northern breeding grounds during summer with progressively lowered influenza prevalence, comprised of a highly diverse profile of subtypes, as waterfowl migrate toward southern wintering grounds. Isolates recovered during winter had the highest proportion of mixed and rare HA/NA combinations, indicating increased opportunity for reassortment of IAVs. In addition, 70% of H5 and 49% of H7 IAV isolates were recovered from samples collected during fall and spring, respectively; these are subtypes that can have significant implications for public health and agriculture sectors. Annual cyclical dominance of subtypes on northern breeding grounds is revealed through the longitudinal nature of this study. Our novel findings exhibit the unrealized potential for discovery using existing IAV surveillance data.IMPORTANCE Wild aquatic birds are the primary natural reservoir of influenza A viruses (IAVs) and are therefore responsible for the dispersal and maintenance of IAVs representing a broad range of antigenic and genetic diversity. The aims of IAV surveillance in waterfowl not only relate to understanding the risk of spillover risk to humans, but also to improving our understanding of basic questions related to IAV evolution and ecology. By evaluating several decades of surveillance data from wild aquatic birds sampled along North American migratory flyways, we discovered an annual trend of increasing subtype diversity during southbound migration, peaking on southern wintering grounds. Winter sampling revealed the highest proportion of mixed and rare infections that suggest higher opportunity for spillover. These findings allow improvements to surveillance efforts to robustly capture IAV diversity that will be used for vaccine development and cultivate a more thorough understanding of IAV evolution and persistence mechanisms.

Spatio-temporal patterns of northern gannet abundance in a migratory and wintering area

In marine ecosystems, seabird populations are well monitored, thus allowing their use as indicators of system fluctuations at multiple spatio-temporal scales. Population abundance estimates are essential features of any conservation and management measures and initiatives. Population abundances can be used to delineate the distribution range and foraging grounds of species during both breeding and non-breeding periods, with multi-annual monitoring allowing for the inspection of the temporal variability within key marine areas. Taking advantage of long-term monitoring schemes, we examined the annual abundance patterns of the northern gannet Morus bassanus in its southern European migratory flyway. Here, the presence of a topographical feature (i.e. a submarine canyon system) could influence physical processes (e.g. upwelling, alongshore currents, and riverine inputs), thus oceanographically differentiating canyon and shelf ecosystems within a spatially restricted marine area. We assessed seasonal and long-term trend fluctuations of monthly northern gannet abundance using Generalized Additive Mixed Models, yielding only a strong seasonal effect. Moreover, we jointly tested the effect of the phenology and the spatial domain (canyon versus shelf) on northern gannet abundance using Generalised Linear Mixed Models, accounting for the excess of zeros. Northern gannet abundance was higher during the pre-winter and post-winter migration, corresponding to its southward and northward movements in the NE Atlantic, respectively. The effect of the canyon was only detected during the post-winter migration. By age, adult northern gannets were more abundant in some periods of the year (from October to March, including the pre-winter migration, the wintering and the post-winter migration), whereas juveniles and immatures were especially abundant during the pre-winter period. Our results could provide quantitative baseline information of northern gannet spatio-temporal patterns in a migratory and wintering area important for both research and conservation efforts, given the high conservation value of the area within the Natura 2000 network.

Migratory Flyways May Affect Population Structure in Double‐Crested Cormorants

ABSTRACTDouble‐crested cormorants (Phalacrocorax auritus) recovered from a demographic bottleneck so well that they are now considered a nuisance species at breeding and wintering grounds across the United States and Canada. Management of this species could be improved by refining genetic population boundaries and assigning individuals to their natal population. Further, recent radio‐telemetry data suggest the existence of Interior and Atlantic migratory flyways, which could reduce gene flow and result in substantial genetic isolation. In this study, we used 1,784 individuals collected across the eastern United States, a large panel of microsatellite markers developed for this species, and individuals banded as chicks and recaptured as adults to explore the effects of migratory flyways on population structure, quantify the genetic effects of demographic bottlenecks, and determine whether individuals could be assigned to their natal population based on genotype. We found evidence for genetic population division only along migratory flyways, no evidence of genetic bottlenecks, and mixed effectiveness of assignment tests. Our population structure findings suggest that gene flow is high across large scales; for example, individuals from New York, Minnesota, and Alabama are all in panmixia. We also found that traditional subspecies ranges may not be valid because >1 subspecies was present in single genetic populations. The lack of evidence for genetic bottlenecks also likely underscores the vagility of this species, suggesting that even during demographic bottlenecks, populations were not isolated from allelic exchange. Finally, the failure of assignment tests to consistently perform is likely due in part to imperfect a priori sampling of Atlantic and Interior chicks and the high vagility of adults. We conclude that the demographic bottleneck is not likely to have reduced genetic diversity, and that assignment tests remain unreliable for this species. We recommend double‐crested cormorants be managed by flyway. Further development of genomic resources in this species could improve population subdivision resolution, improve assignment tests, and reveal further information on demographic histories. © 2020 The Wildlife Society.

Broad‐scale patterns of the Afro‐Palaearctic landbird migration

AbstractAimKnowledge of broad‐scale biogeographical patterns of animal migration is important for understanding ecological drivers of migratory behaviours. Here, we present a flyway‐scale assessment of the spatial structure and seasonal dynamics of the Afro‐Palaearctic bird migration system and explore how phenology of the environment guides long‐distance migration.LocationEurope and Africa.Time period2009–2017.Major taxa studiedBirds.MethodsWe compiled an individual‐based dataset comprising 23 passerine and near‐passerine species of 55 European breeding populations, in which a total of 564 individuals were tracked during migration between Europe and sub‐Saharan Africa. In addition, we used remotely sensed primary productivity data (the normalized difference vegetation index) to estimate the timing of vegetation green‐up in spring and senescence in autumn across Europe. First, we described how individual breeding and non‐breeding sites and the migratory flyways link geographically. Second, we examined how the timing of migration along the two major Afro‐Palaearctic flyways is tuned with vegetation phenology at the breeding sites.ResultsWe found the longitudes of individual breeding and non‐breeding sites to be related in a strongly positive manner, whereas the latitudes of breeding and non‐breeding sites were related negatively. In autumn, migration commenced ahead of vegetation senescence, and the timing of migration was 5–7 days earlier along the Western flyway compared with the Eastern flyway. In spring, the time of arrival at breeding sites was c. 1.5 days later for each degree northwards and 6–7 days later along the Eastern compared with the Western flyway, reflecting the later spring green‐up at higher latitudes and more eastern longitudes.Main conclusionsMigration of the Afro‐Palaearctic landbirds follows a longitudinally parallel leapfrog migration pattern, whereby migrants track vegetation green‐up in spring but depart before vegetation senescence in autumn. The degree of continentality along migration routes and at the breeding sites of the birds influences the timing of migration on a broad scale.

High Prevalence of Avian Influenza Virus Among Wild Waterbirds and Land Birds of Mexico.

Aquatic wild birds, especially waterfowl, have been long considered the main reservoirs of the avian influenza A virus; however, recent surveys have found an important prevalence of these viruses among land birds as well. Migration has been suggested as an important factor in the avian influenza virus dissemination. We aimed to estimate the prevalence of influenza A viruses in wild birds (waterbirds and land birds; resident and migratory) in eastern Mexico, where the three main North American migration flyways converge and where there was no previous information on this subject. We detected influenza with reverse transcription coupled with a PCR approach. Of the 534 birds sampled between 2010 and 2012, we detected the influenza A virus in a high proportion of birds (39%). Prevalence was particularly high in land birds (49%) when compared to aquatic birds (26%); there was no difference in overall prevalence between resident (39%) and migratory birds (39%). The high prevalence of the avian influenza virus in land birds was noteworthy in the innermost sampling areas in northern Mexico (Coahuila [82%] and Nuevo Leon [43%]).

Sea-Crossing Along Migratory Flyways is More Strongly Limited by Wind than by Lack of Uplift

The open sea is considered an ecological barrier to terrestrial bird movement. However, over-water journeys of many terrestrial birds, sometimes hundreds of kilometers long, are being uncovered by bio-logging technology. To understand how these birds afford their flights over the open sea, we investigated the role of atmospheric conditions in subsidizing sea-crossing behavior at the global scale. By analyzing forty years of temperature data, we show that the spatio-temporal patterns of sea-crossing in terrestrial migratory birds correspond to favorable uplift conditions. We then analyzed route selection over the open sea for four bird species with varying levels of dependence on soaring flight, representing all major migratory flyways worldwide. Our results showed that favorable uplift conditions, albeit not as common and powerful as over land, are not rare over the open seas and oceans. Moreover, wind, which is more variable than uplift in its spatio-temporal distribution, is the determining factor in the birds' route selection over the open sea. Our findings suggest a need for revisiting how ecological barriers are defined, to reflect what we know of animal movement in the era of bio-logging.

Characterization and Phylodynamics of Reassortant H12Nx Viruses in Northern Eurasia.

Wild waterfowl birds are known to be the main reservoir for a variety of avian influenza viruses of different subtypes. Some subtypes, such as H2Nx, H8Nx, H12Nx, and H14Nx, occur relatively rarely in nature. During 10-year long-term surveillance, we isolated five rare H12N5 and one H12N2 viruses in three different distinct geographic regions of Northern Eurasia and studied their characteristics. H12N2 from the Far East region was a double reassortant containing hemagglutinin (HA), non-structural (NS) and nucleoprotein (NP) segments of the American lineage and others from the classical Eurasian avian-like lineage. H12N5 viruses contain Eurasian lineage segments. We suggest a phylogeographical scheme for reassortment events associated with geographical groups of aquatic birds and their migration flyways. The H12N2 virus is of particular interest as this subtype has been found in common teal in the Russian Far East region, and it has a strong relation to North American avian influenza virus lineages, clearly showing that viral exchange of segments between the two continents does occur. Our results emphasize the importance of Avian Influenza Virus (AIV) surveillance in Northern Eurasia for the annual screening of virus characteristics, including the genetic constellation of rare virus subtypes, to understand the evolutionary ecology of AIV.

Analysis of Bird Flyways in 3D

Bird migration is a long studied phenomenon that involves animals moving back and forth from wintering sites and to reproductive grounds. Several studies have focused on identifying the timing, physiology and evolution of migration, but a spatial approach to understand the migratory routes is still an open challenge. Geographic Information Systems (GIS) can provide the tools to explore such a complicated issue. Birds usually move from the wintering sites to spring breeding grounds in multiple flights, stopping at intermediate sites to rest and refuel, being unable to cover the distance in a single travel. The choice of stopover sites by birds depends not only on their ecological features but also on their position and visibility along main migratory flyways. In this work, we calculated the possible migratory routes that minimize the distance covered or the elevation gaps for birds crossing the Southern Alps, simulating the flight within a network connecting potential stopover sites and other relevant point of passage, using the shortest path computation. Subsequently, we performed a visibility analysis along the identified flyways to understand which stopover sites, belonging to the Natura2000 network, were visible for a bird in an area with complex morphology. Data available from ringing stations confirm the selection or avoidance of some stopover sites based on their en route visibility. The knowledge of bird flyways and stopover sites has implications for conservation as well as for planning, especially for wind farms or other infrastructures.