Comparative migration strategies of wild and captive‐bred Asian Houbara Chlamydotis macqueenii

For migratory species, the success of population reintroduction or reinforcement through captive‐bred released individuals depends on survivors undertaking appropriate migrations. We assess whether captive‐bred Asian Houbara Chlamydotis macqueenii from a breeding programme established with locally sourced individuals and released into suitable habitat during spring or summer undertake similar migrations to those of wild birds. Using satellite telemetry, we compare the migrations of 29 captive‐bred juveniles, 10 wild juveniles and 39 wild adults (including three birds first tracked as juveniles), examining migratory propensity (proportion migrating), timing, direction, stopover duration and frequency, efficiency (route deviation), and wintering and breeding season locations. Captive‐bred birds initiated autumn migration an average of 20.6 (±4.6 se) days later and wintered 470.8 km (±76.4) closer to the breeding grounds, mainly in Turkmenistan, northern Iran and Afghanistan, than wild birds, which migrated 1217.8 km (±76.4), predominantly wintering in southern Iran and Pakistan (juveniles and adults were similar). Wintering locations of four surviving captive‐bred birds were similar in subsequent years (median distance to first wintering site = 70.8 km, range 6.56–221.6 km), suggesting that individual captive‐bred birds (but not necessarily their progeny) remain faithful to their first wintering latitude. The migratory performance of captive‐bred birds was otherwise similar to that of wild juveniles. Although the long‐term fitness consequences for captive‐bred birds establishing wintering sites at the northern edge of those occupied by wild birds remain to be quantified, it is clear that the pattern of wild migrations established by long‐term selection is not replicated. If the shorter migration distance of young captive‐bred birds has a physiological rather than a genetic basis, then their progeny may still exhibit wild‐type migration. However, as there is a considerable genetic component to migration, captive breeding management must respect migratory population structure as well as natal and release‐site fidelity.     

Wild Mallards Have More “Goose-Like” Bills Than Their Ancestors: A Case of Anthropogenic Influence?

Wild populations of the world’s most common dabbling duck, the mallard (Anas platyrhynchos), run the risk of genetic introgression by farmed conspecifics released for hunting purposes. We tested whether bill morphology of free-living birds has changed since large-scale releases of farmed mallards started. Three groups of mallards from Sweden, Norway and Finland were compared: historical wild (before large-scale releases started), present-day wild, and present-day farmed. Higher density of bill lamellae was observed in historical wild mallards (only males). Farmed mallards had wider bills than present-day and historical wild ones. Present-day wild and farmed mallards also had higher and shorter bills than historical wild mallards. Present-day mallards thus tend to have more “goose-like” bills (wider, higher, and shorter) than their ancestors. Our study suggests that surviving released mallards affect morphological traits in wild population by introgression. We discuss how such anthropogenic impact may lead to a maladapted and genetically compromised wild mallard population. Our study system has bearing on other taxa where large-scale releases of conspecifics with ‘alien genes’ may cause a cryptic invasive process that nevertheless has fitness consequences for individual birds.     

Impact of hand-rearing on morphology and physiology of the capercaillie (Tetrao urogallus)

Morphological and physiological disparities between 20 captive and 11 wild capercaillies were determined. Birds, their pectoral and leg muscles, hearts, livers and gizzards were weighed. The length of small intestines and caeca were measured. Haemoglobin, haematocrit, glucose, triglycerides, total protein, uric acid and thyroid hormones as well as the cytochrome c-oxidase activity of the pectoral muscle and heart were determined. The glycogen and protein contents of pectoral and leg muscles and liver were analysed. Chemical composition (water, fat, protein, ash) of muscles and liver was determined. Captive males had heavier pectoral muscles than wild ones. The result was opposite in females. Wild birds had heavier hearts, livers, and gizzards, and also longer small intestines and caeca than captive birds. The cytochrome c-oxidase activity of pectoral muscle and heart was higher in wild than in hand-reared birds. The chemical composition of livers of wild birds differed significantly from that of hand-reared capercaillies. Plasma uric acid and T(4) concentrations were higher in captive than in wild birds. The observed differences in digestive system and liver can result in diminished ability of captive birds to utilise natural food nutrients. Decreased cytochrome c-oxidase activity of hand-reared birds can affect their takeoff and flying capacity and increase their vulnerability to predation. These facts may contribute to the low survival of hand-reared birds after release.     

Seasonal migrations of four individual bar-headed geese Anser indicus from Kyrgyzstan followed by satellite telemetry

The Kyrgyz population of the bar-headed goose Anser indicus has declined dramatically during the past decades. Human persecution during migration and habitat loss at stopover and wintering sites are commonly regarded as most serious threats. However, little is known about seasonal movements, migration routes, and wintering sites of the bar-headed geese from Kyrgyzstan, which represent the westernmost geographical population of the species. As part of a conservation project, which also included reinforcement of the wild population by the release of hand-reared juveniles, in late summer of 1998, five bar-headed geese, three wild adults and two hand-reared goslings, were fitted with sun-powered satellite transmitters in order to track their movements from Lake Son Kul and Lake Chatyr Kul in Kyrgyzstan. The five individuals contributed very unevenly to the more than 5,000 signals in total that were received from the French ARGOS system: one failed after 8 weeks, while another one was tracked for more than 2 years. The four geese contributing to this study followed three completely different migration routes leading to their wintering areas in Pakistan, India and Uzbekistan, while stopover areas were situated in southern Tajikistan and in western Tibet. Both in autumn and spring the adult birds migrated distances of 1,280–1,550 km in two steps, with stopover periods of 32–46 days (autumn) and 16–23 days (spring). Flight speeds of up to 680 km per actual migration day were recorded regularly, even during crossings of very high summits. A hand-reared juvenile flew non-stop for 790 km to southern Uzbekistan and even visited southernmost Turkmenistan, where the species is very rarely seen. The timing of migration varied considerably between individuals but also for the same individual between years. We compare our tracking results with previous findings (field observations, ring recoveries, and satellite tracking results) and discuss them with respect to migration over high-mountain habitats and a general migration strategy of the species.     

Diffuse, short and slow migration among Blue Tits

The knowledge of migration systems in long-distance regular migrants is in many cases extensive. Our understanding of the migratory characteristics of partial migrants, on the other hand, is far more rudimentary. We investigated migratory characteristics of partially migratory Blue Tits Cyanistes caeruleus using ringing recoveries of Swedish birds, to answer questions about geographic migration patterns, age-specific migrations, migration speeds and synchrony of movements. Median migration distance of Swedish Blue Tits was 82 km, with a main autumn direction in the sector between S and W (large directional scatter). Northerly and southerly populations did not differ in migration directions or distances, suggesting chain migration to be the general pattern. A larger proportion of adult Blue Tits remained near the breeding grounds during winter than was the case for juveniles. Some of the migrating birds (17%) seemed not to return in spring but stayed to breed closer to the winter area. Swedish Blue Tits show an exceptionally slow migration speed (median 13 km/day), among the slowest speeds recorded for any migrant bird. The Blue Tit represents an extreme case of diffuse, short and slow bird migration.     

Assessing changes in genomic divergence following a century of human‐mediated secondary contact among wild and captive‐bred ducks

Along with manipulating habitat, the direct release of domesticated individuals into the wild is a practice used worldwide to augment wildlife populations. We test between possible outcomes of human‐mediated secondary contact using genomic techniques at both historical and contemporary timescales for two iconic duck species. First, we sequence several thousand ddRAD‐seq loci for contemporary mallards (Anas platyrhynchos) throughout North America and two domestic mallard types (i.e., known game‐farm mallards and feral Khaki Campbell's). We show that North American mallards may well be becoming a hybrid swarm due to interbreeding with domesticated game‐farm mallards released for hunting. Next, to attain a historical perspective, we applied a bait‐capture array targeting thousands of loci in century‐old (1842–1915) and contemporary (2009–2010) mallard and American black duck (Anas rubripes) specimens. We conclude that American black ducks and mallards have always been closely related, with a divergence time of ~600,000 years before present, and likely evolved through prolonged isolation followed by limited bouts of gene flow (i.e., secondary contact). They continue to maintain genetic separation, a finding that overturns decades of prior research and speculation suggesting the genetic extinction of the American black duck due to contemporary interbreeding with mallards. Thus, despite having high rates of hybridization, actual gene flow is limited between mallards and American black ducks. Conversely, our historical and contemporary data confirm that the intensive stocking of game‐farm mallards during the last ~100 years has fundamentally changed the genetic integrity of North America's wild mallard population, especially in the east. It thus becomes of great interest to ask whether the iconic North American mallard is declining in the wild due to introgression of maladaptive traits from domesticated forms. Moreover, we hypothesize that differential gene flow from domestic game‐farm mallards into the wild mallard population may explain the overall temporal increase in differentiation between wild black ducks and mallards, as well as the uncoupling of genetic diversity and effective population size estimates across time in our results. Finally, our findings highlight how genomic methods can recover complex population histories by capturing DNA preserved in traditional museum specimens.     

African Odyssey project – satellite tracking of black storks Ciconia nigra breeding at a migratory divide

The African Odyssey project focuses on studying the migration of the black stork Ciconia nigra breeding at a migratory divide. In 1995–2001, a total of 18 black storks breeding in the Czech Republic were equipped with satellite (PTT) and VHF transmitters. Of them, 11 birds were tracked during at least one migration season and three birds were tracked repeatedly. The birds migrated either across western or eastern Europe to spend the winter in tropical west or east Africa, respectively. One of the juveniles made an intermediate route through Italy where it was shot during the first autumn migration. The mean distance of autumn migration was 6,227 km. The eastern route was significantly longer than the western one (7,000 km and 5,667 km respectively). Important stopover sites were discovered in Africa and Israel. Wintering areas were found from Mauritania and Sierra Leone in the west to Ethiopia and Central African Republic in the east and south. One of the storks migrating by the eastern migration route surprisingly reached western Africa. Birds that arrived early in the wintering areas stayed longer than those arriving later. On the average, birds migrating via the western route spent 37 d on migration compared to 80 d for birds migrating via the eastern route. The mean migration speed in the autumn was 126 km/d and the fastest stork flew 488 km/d when crossing the Sahara. The repeatedly tracked storks showed high winter site fidelity.     

Fitness Evaluation of <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> Exposed to Ni

The study aimed at determining the degree of mercury contamination of mallards, game waterbirds migrating from the regions of the unknown degree of contamination and establishing whether the consumption of their meat comprises a hazard to human health in view of the binding norms concerning the mercury content in food products. The investigations were carried out on 30 mallards shot during the duck shooting season in which mercury concentrations in the muscles, liver, and kidneys were determined using the cold vapor atomic absorption spectrometry (CV-AAS) method. The mean Hg concentration in the investigated tissues in all birds studied amounted to 0.110, 0.154, and 0.122 mg kg^?1 for the muscles, kidneys, and liver, respectively. The study indicated statistically significant (p ≤ 0.01) positive correlation between all of the organs examined. Animals were divided into two groups differing in both absolute values of Hg concentrations and those measured in individual tissues. In particular organs of birds representing the first group, the presence of highly significant correlation (p ≤ 0.01) was observed in all organs examined. In the second group, highly significant positive correlation between Hg concentrations in the liver and kidneys and highly significant negative dependence between the liver and muscles was noted. The examinations revealed that some birds must have come from regions of a high degree of mercury contamination.     

Migration distance does not predict blood parasitism in a migratory songbird

Migration can influence host–parasite dynamics in animals by increasing exposure to parasites, by reducing the energy available for immune defense, or by culling of infected individuals. These mechanisms have been demonstrated in several comparative analyses; however, few studies have investigated whether conspecific variation in migration distance may also be related to infection risk. Here, we ask whether autumn migration distance, inferred from stable hydrogen isotope analysis of summer‐grown feathers (δ²H_f) in Europe, correlates with blood parasite prevalence and intensity of infection for willow warblers (Phylloscopus trochilus) wintering in Zambia. We also investigated whether infection was correlated with individual condition (assessed via corticosterone, scaled mass index, and feather quality). We found that 43% of birds were infected with Haemoproteus palloris (lineage WW1). Using generalized linear models, we found no relationship between migration distance and either Haemoproteus infection prevalence or intensity. There was spatial variation in breeding ground origins of infected versus noninfected birds, with infected birds originating from more northern sites than noninfected birds, but this difference translated into only slightly longer estimated migration distances (~214 km) for infected birds. We found no relationship between body condition indices and Haemoproteus infection prevalence or intensity. Our results do not support any of the proposed mechanisms for migration effects on host–parasite dynamics and cautiously suggest that other factors may be more important for determining individual susceptibility to disease in migratory bird species.     

Migration strategy affects avian influenza dynamics in mallards (Anas platyrhynchos)

Studies of pathogen transmission typically overlook that wildlife hosts can include both migrant and resident populations when attempting to model circulation. Through the application of stable isotopes in flight feathers, we estimated the migration strategy of mallards (Anas platyrhynchos) occurring on California wintering grounds. Our study demonstrates that mallards‐ a principal host of avian influenza virus (AIV) in nature, contribute differently to virus gene flow depending on migration strategy. No difference in AIV prevalence was detected between resident (9.6%), intermediate‐distance (9.6%) and long‐distance migrants (7.4%). Viral diversity among the three groups was also comparable, possibly owing to viral pool mixing when birds converge at wetlands during winter. However, migrants and residents contributed differently to the virus gene pool at wintering wetlands. Migrants introduced virus from northern breeding grounds (Alaska and the NW Pacific Rim) into the wintering population, facilitating gene flow at continental scales, but circulation of imported virus appeared to be limited. In contrast, resident mallards acted as AIV reservoirs facilitating year‐round circulation of limited subtypes (i.e. H5N2) at lower latitudes. This study supports a model of virus exchange in temperate regions driven by the convergence of wild birds with separate geographic origins and exposure histories.     

Satellite tracking of Swedish Ospreys Pandion haliaetus: autumn migration routes and orientation

Autumn migration routes and orientation of Swedish Ospreys Pandion haliaetus were studied by satellite tracking of 18 birds. Of these, 13 could be followed during the entire migration (6 females, 5 males and 2 juveniles). Most birds migrated across western and central Europe to winter in tropical West Africa. However, one juvenile flew to Cameroon and one female used a very easterly route and reached Mozambique. On average, the birds travelled a total distance of about 6700 km, with little variation except for the female wintering in Mozambique, who travelled more than 10 000 km. Of 21 stopovers (of >1 day), only five were made south of 45°N; three of these in Africa. Females departed before males and juveniles and flew to a stopover site they probably were familiar with. After 3–4 weeks there, they continued to their wintering grounds. Also males and juveniles usually made one or more stopovers. Adults seemed to travel to a known wintering site, where they remained stationary, whereas juveniles were more mobile after reaching tropical regions, probably looking for good wintering sites. Males generally left the breeding area in directions similar to the mean migratory direction, whereas a few females departed in diverging initial directions. Apart from these diversions, adult Ospreys followed very straight migratory routes, with overall mean directions of 185–209° and with mean angular deviations of 6–33°. Some juveniles also departed in diverging directions. Moreover, young birds tended to show a larger variability in orientation. Thus, the Ospreys kept a fairly straight direction and did not avoid geographical obstacles such as mountain ranges and desert areas. However, they seemed reluctant to cross large water bodies. There was no correlation between angular deviation and length of the migrational segment, indicating that the principles of orientation by vector summation may not be valid for Osprey migration. Moreover, the geographic direction of migration did not vary in accordance with variations in the magnetic declination, suggesting that the Ospreys did not orient along magnetic loxodromes.     

A robust tool highlights the influence of bird migration on influenza A virus evolution

One of the fundamental unknowns in the field of influenza biology is a panoramic understanding of the role wild birds play in the global maintenance and spread of influenza A viruses. Wild aquatic birds are considered a reservoir host for all lowly pathogenic avian influenza A viruses (AIV) and thus serve as a potential source of zoonotic AIV, such as Australasian‐origin H5N1 responsible for morbidity and mortality in both poultry and humans, as well as genes that may contribute to the emergence of pandemic viruses. Years of broad, in‐depth wild bird AIV surveillance have helped to decipher key observations and ideas regarding AIV evolution and viral ecology including the trending of viral lineages, patterns of gene flow within and between migratory flyways and the role of geographic boundaries in shaping viral evolution (Bahl et al. 2009 ; Lam et al. 2012 ). While these generally ‘virus‐centric’ studies have ultimately advanced our broader understanding of AIV dynamics, recent studies have been more host‐focused, directed at determining the potential impact of host behaviour on AIV, specifically, the influence of bird migration upon AIV maintenance and transmission. A large number of surveillance studies have taken place in Alaska, United States—a region where several global flyways overlap—with the aim of detecting the introduction of novel, Australasian‐origin highly pathogenic H5N1 AIV into North America. By targeting bird species with known migration habits, long‐distance migrators were determined to be involved in the intercontinental movement of individual AIV gene segments, but not entire viruses, between the Australasian and North American flyways (Koehler et al. 2008 ; Pearce et al. 2010 ). Yet, bird movement is not solely limited to long‐distance migration, and the relationship of resident or nonmigratory and intermediate‐distance migrant populations with AIV ecology has only recently been explored by Hill et al. ( 2012 ) in this issue of Molecular Ecology. Applying a uniquely refined, multidimensional approach, Hill et al. validate the innovative use of stable isotope assays for qualifying migration status of wild mallards within the Pacific flyway. The authors reveal that AIV prevalence and diversity did not differ in wintering mallard ducks with different migration strategies, and while migrant mallards do indeed introduce AIV, these viruses do not circulate as the predominant viruses in resident birds. On the other hand, resident mallards from more temperate regions act as reservoirs, possibly contributing to the unseasonal circulation and extended transmission period of AIV. This study highlights the impact of animal behaviour on shaping viral evolution, and the unique observations made will help inform prospective AIV surveillance efforts in wild birds.     

Population Genetics of a Translocated Population of Mottled Ducks and Allies

Translocating species is an important management tool to establish or expand the range of species. Success of translocations requires an understanding of potential consequences, including whether a sufficient number of individuals were used to minimize founder effects and if interspecific hybridization poses a threat. We provide an updated and comprehensive genetic assessment of a 1970s–1980s translocation and now established mottled duck (Anas fulvigula) population in South Carolina, USA. In addition to examining the population genetics of these mottled ducks, we simulated expected genetic assignments for generational hybrids (F1–F10), permitting formal purity assignment across samples to identify true hybrids and establish hybridization rates. In addition to wild mallards (A. platyrhynchos), we tested for presence of hybrids with migrant American black ducks (A. rubripes) and released domestic game-farm mallards (A. p. domesticus). We used wild reference populations of North American mallard-like ducks and sampled game-farm mallards from 2 sites in South Carolina that could potentially interbreed with mottled ducks. Despite 2 different subspecies of mottled duck (Florida [A. f. fulvigula] and the Western Gulf Coast [A. f. maculatlus]) used in original translocations, we determined the gene pool of the Western Gulf Coast mottled duck was overwhelmingly represented in South Carolina's current population. We found no evidence of founder effects or inbreeding and concluded the original translocation of 1,285 mottled ducks was sufficient to maintain current genetic diversity. We identified 7 hybrids, including an F1 and 3 late-staged (i.e., F2–F3 backcrosses) mottled duck × black duck hybrids, 1 F2-mottled duck backcrossed with a wild mallard, and 2 F3-mottled ducks introgressed with game-farm mallard. We estimated a 15% hybridization rate in our mottled duck dataset; however, the general lack of F1 and intermediate hybrids were inconsistent with scenarios of high hybridization rates or presence of a hybrid swarm. Instead, our results suggested a scenario of infrequent interspecific hybridization between South Carolina's mottled ducks and congeners. We concluded that South Carolina's mottled duck population is sufficiently large now to absorb current hybridization rates because 85% of sampled mottled ducks were pure. These results demonstrate the importance in managing and maintaining large parental populations to counter hybridization. As such, future population management of mottled ducks in South Carolina will benefit from increased geographical and continued sampling to monitor hybridization rates with closely related congeners. We also suggest that any future translocations of mottled ducks to coastal South Carolina should originate from the Western Gulf Coast. © 2021 The Wildlife Society.     

Artificial incubation and hand-rearing of 'Alala (Corvus hawaiiensis) eggs removed from the wild

The wild 'Alala (Corvus hawaiiensis) population has been declining for many years, and only a few pairs of birds are currently reproductively active on the island of Hawaii. A recovery program was initiated in 1993 which included removing eggs from wild nesting birds for artificial rearing and reintroduction. This paper describes the artificial incubation and hand-rearing techniques. Eleven eggs were removed from three nesting pairs; eight were fertile, and seven hatched and were hand-reared (fertility, 72.7%; hatchability, 87.5%; survivability, 100%). Eggs were incubated in a forced-air incubator at 99.5°F (dry bulb), 80.0–86.0°F (wet bulb), and hatched under still-air conditions at 99.0°F (dry bulb) and 88.0–90°F (wet bulb). Hatched chicks were hand-fed a diet of fruit, insects, and mouse pups. © 1994 Wiley-Liss, Inc.     

Genetic structure of Eurasian and North American mallard ducks based on mtDNA data

To elucidate the origin and genetic structure of the domesticated duck in Eurasia and North America, we sequenced 114 duck D-loop sequences and retrieved 489 D-loop sequences from GenBank. In total, 603 ducks including 50 duck breeds/populations from eight countries (China, France, Russia, India, Kazakhstan, Mongolia, Thailand and USA) were used in this study. One hundred and thirty-four haplotypes and 81 variable sites were detected. H49 was the predominant haplotype, which was considered to be the same dominant haplotype found in the previous studies, and was found in 309 birds. The smallest values for both genetic differentiation index (F(ST), 0.04156) and the number of the net nucleotide substitutions between two populations (D(A), 0.00018) were observed between Eurasian domestic ducks and Eurasian mallards. No geography, breed or population clusters were observed in the Eurasian domestic ducks and mallards. Five haplotypes were shared by USA mallards and Eurasian domestic duck/Eurasian mallards. Only one haplotype (H49) was shared by Eurasian domestic ducks and China spot-billed ducks. By combining phylogenetic analyses, haplotype network profile, genetic distances and shared haplotypes, we can draw two major conclusions: (i) Eurasian and North American mallards show a clear geographic distribution pattern; (ii) Eurasian domestic ducks are derived from the Eurasian mallards, not from the spot-billed ducks.     

Genome wide SNP discovery,analysis and evaluation in mallard (<Emphasis Type="Italic">Anas platyrhynchos</Emphasis>)

Background

Next generation sequencing technologies allow to obtain at low cost the genomic sequence information that currently lacks for most economically and ecologically important organisms. For the mallard duck genomic data is limited. The mallard is, besides a species of large agricultural and societal importance, also the focal species when it comes to long distance dispersal of Avian Influenza. For large scale identification of SNPs we performed Illumina sequencing of wild mallard DNA and compared our data with ongoing genome and EST sequencing of domesticated conspecifics. This is the first study of its kind for waterfowl.

Results

More than one billion base pairs of sequence information were generated resulting in a 16× coverage of a reduced representation library of the mallard genome. Sequence reads were aligned to a draft domesticated duck reference genome and allowed for the detection of over 122,000 SNPs within our mallard sequence dataset. In addition, almost 62,000 nucleotide positions on the domesticated duck reference showed a different nucleotide compared to wild mallard. Approximately 20,000 SNPs identified within our data were shared with SNPs identified in the sequenced domestic duck or in EST sequencing projects. The shared SNPs were considered to be highly reliable and were used to benchmark non-shared SNPs for quality. Genotyping of a representative sample of 364 SNPs resulted in a SNP conversion rate of 99.7%. The correlation of the minor allele count and observed minor allele frequency in the SNP discovery pool was 0.72.

Conclusion

We identified almost 150,000 SNPs in wild mallards that will likely yield good results in genotyping. Of these, ~101,000 SNPs were detected within our wild mallard sequences and ~49,000 were detected between wild and domesticated duck data. In the ~101,000 SNPs we found a subset of ~20,000 SNPs shared between wild mallards and the sequenced domesticated duck suggesting a low genetic divergence. Comparison of quality metrics between the total SNP set (122,000 + 62,000 = 184,000 SNPs) and the validated subset shows similar characteristics for both sets. This indicates that we have detected a large amount (~150,000) of accurately inferred mallard SNPs, which will benefit bird evolutionary studies, ecological studies (e.g. disentangling migratory connectivity) and industrial breeding programs.

     

Mallard Response to Experimental Walk-In and Shooting Disturbance

ABSTRACT Spatial and temporal closures of anthropogenic activities are a common management strategy to increase waterfowl usage of an area. However, empirical evidence, specifically how individual waterfowl respond to disturbance, is lacking to support their efficacy. We exposed radiomarked mallards (Anas platyrhynchos) to walk-in, shooting, or no disturbance along the South Platte River corridor in Colorado, USA, from September to February during 2006–2007 and 2007–2008. Mallards exposed to shooting disturbance had greater mean flight distance after disturbance (FDAD) during September-November (4.58 km, 95% CI = 3.55–5.62) than December-February (3.04 km, 95% CI = 2.51–3.58) and were 35% and 17% greater than mean FDAD of mallards exposed to walk-in disturbance, respectively. Walk-in and shooting disturbance had a similar effect on return rates, and disturbed mallards had higher (0.09–0.41) movement probabilities away from and lower (0.15–0.20) probabilities of returning to treatment locations than controls. Probability of presence of disturbed mallards was 37% lower than controls during the daytime but was equal at night. Mallards exposed to walk-in (0.38 [95% CI = 0.30–0.46]) and shooting (0.23 [95% CI = 0.17–0.30] disturbance had low return rates the first afternoon after a disturbance compared to controls (0.71 [95% CI = 0.65–0.77]). A high proportion of mallards exposed to walk-in (0.75 [95% CI = 0.67–0.83]) and shooting (0.70 [95% CI = 0.64–0.76]) disturbance returned to treatment locations in ≤1 day. Managers may be able to more effectively manage disturbance regimes by 1) accounting for surrounding lands within <10 km, especially lands within <5 km, 2) being conscientious when establishing regulations that will affect levels of disturbance 1–2 days after a previous disturbance, and 3) considering shooting and walking disturbance equally for refuge design.     

Potential seed dispersal distances of native and non-native fleshy fruiting shrubs in the South African Mediterranean climate region

Bird flight distances for the small Zosterops capensis, the medium-size Pycnonotus capensis and the large Colius striatus were extracted from these birds’ initial ring and subsequent recapture locations and expressed on equivalent per km bases. The products of the bird-ring recapture records in nine different flight distance categories and daily consumption rates by these birds of seeds of two native (Chrysanthemoides monilifera and Olea europaea spp. africana) and two alien (Lantana camara and Solanum mauritianum) shrubs were used to construct seed dispersal curves. The dispersal distances to which ingested seeds were theoretically restricted were computed from the product of the retention time of seed in the birds’ guts and their flight speeds using published functions. All three bird species displayed thin long-tailed seed dispersal curves characterized by peaks at distances below 1 km which declined progressively with increasing distances, the tails extending to distances of up to 400 km. Flight distances corresponding with predicted seed gut retention times were 9.4 km in the small Z. capensis, 17.8 km in the medium size P. capensis and 21.2 km in the large C. striatus. These potential seed dispersal distances were much greater that the frequently reported long distance seed dispersal threshold of 1 km by frugivorous birds in fragmented landscapes.     

Effects of Local and Landscape Variables on Wetland Bird Habitat Use During Migration Through the Rainwater Basin

ABSTRACT Staging areas and migratory stopovers of wetland birds can function as geographic bottlenecks; common dependence among migratory wetland bird species on these sites has major implications for wetland conservation. Although 90% of playa wetlands in the Rainwater Basin (RWB) region of Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for up to 10 million waterfowl each spring. Our objectives were to determine local (within wetland and immediate watershed) and landscape-scale factors influencing wetland bird abundance and species richness during spring migration at RWB playas. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 1.6 million individual migratory wetland birds representing 72 species during spring migrations 2002–2004. We tested a priori hypotheses about whether local and landscape variables influenced overall species richness and abundance of geese, dabbling ducks, diving ducks, and shorebirds. Wetland area had a positive influence on goose abundance in all years, whereas percent emergent vegetation and hunting pressure had negative influences. Models predicting dabbling duck abundance differed among years; however, individual wetland area and area of semipermanent wetlands within 10 km of the study wetland consistently had a positive influence on dabbling duck abundance. Percent emergent vegetation also was a positive predictor of dabbling duck abundance in all years, indicating that wetlands with intermediate (50%) vegetation coverage have the greatest dabbling duck abundance. Shorebird abundance was positively influenced by wetland area and number of wetlands within 10 km and negatively influenced by water depth. Wetland area, water depth, and area of wetlands within 10 km were all equally important in models predicting overall species richness. Total species richness was positively influenced by wetland area and negatively influenced by water depth and area of semipermanent wetlands within 10 km. Avian species richness also was greatest in wetlands with intermediate vegetation coverage. Restoring playa hydrology should promote intermediate percent cover of emergent vegetation, which will increase use by dabbling ducks and shorebirds, and decrease snow goose (Chen caerulescens) use of these wetlands. We observed a reduction in dabbling duck abundance on wetlands open to spring snow goose hunting and recommend further investigation of the effects of this conservation order on nontarget species. Our results indicate that wildlife managers at migration stopover areas should conserve wetlands in complexes to meet the continuing and future habitat requirements of migratory birds, especially dabbling ducks, during spring migration.     

The annual cycle of a trans-equatorial Eurasian-African passerine migrant: different spatio-temporal strategies for autumn and spring migration

The small size of the billions of migrating songbirds commuting between temperate breeding sites and the tropics has long prevented the study of the largest part of their annual cycle outside the breeding grounds. Using light-level loggers (geolocators), we recorded the entire annual migratory cycle of the red-backed shrike Lanius collurio, a trans-equatorial Eurasian-African passerine migrant. We tested differences between autumn and spring migration for nine individuals. Duration of migration between breeding and winter sites was significantly longer in autumn (average 96 days) when compared with spring (63 days). This difference was explained by much longer staging periods during autumn (71 days) than spring (9 days). Between staging periods, the birds travelled faster during autumn (356 km d(-1)) than during spring (233 km d(-1)). All birds made a protracted stop (53 days) in Sahelian sub-Sahara on southbound migration. The birds performed a distinct loop migration (22 000 km) where spring distance, including a detour across the Arabian Peninsula, exceeded the autumn distance by 22 per cent. Geographical scatter between routes was particularly narrow in spring, with navigational convergence towards the crossing point from Africa to the Arabian Peninsula. Temporal variation between individuals was relatively constant, while different individuals tended to be consistently early or late at different departure/arrival occasions during the annual cycle. These results demonstrate the existence of fundamentally different spatio-temporal migration strategies used by the birds during autumn and spring migration, and that songbirds may rely on distinct staging areas for completion of their annual cycle, suggesting more sophisticated endogenous control mechanisms than merely clock-and-compass guidance among terrestrial solitary migrants. After a century with metal-ringing, year-round tracking of long-distance migratory songbirds promises further insights into bird migration.