Stable Isotope Analysis Of Feathers Research Articles

Stable Isotope Analysis of Feathers as a Potential Method for Distinguishing Individual Birds

Stable Isotope Analysis of Feathers as a Potential Method for Distinguishing Individual Birds

Annual movements of a migratory seabird—the NW European red-throated diver (Gavia stellata)—reveals high individual repeatability but low migratory connectivity

In this study, the annual movements of a seabird species, the red-throated diver (Gavia stellata), were investigated in space and time. Between 2015 and 2017, 33 individuals were fitted with satellite transmitters at the German Bight (eastern North Sea). In addition, stable isotope analyses of feathers (δ13C) were used to identify staging areas during the previous moult. The German Bight is an important area for this species, but is also strongly affected by anthropogenic impacts. To understand how this might affect populations, we aimed to determine the degree of connectivity and site fidelity, and the extent to which seasonal migrations vary among different breeding locations in the high Arctic. Tagged individuals migrated to Greenland (n = 2), Svalbard (n = 2), Norway (n = 4) and northern Russia (n = 25). Although individuals from a shared breeding region (northern Russia) largely moved along the same route, individuals dispersed to different, separate areas during the non-breeding phase. Kernel density estimates also overlapped only partially, indicating low connectivity. The timing of breeding was correlated with the breeding longitude, with 40 days later arrival at the easternmost than westernmost breeding sites. Repeatability analyses between years revealed a generally high individual site fidelity with respect to spring staging, breeding and moulting sites. In summary, low connectivity and the distribution to different sites suggests some resilience to population decline among subpopulations. However, it should be noted that the majority of individuals breeding in northern Russia migrated along a similar route and that disturbance in areas visited along this route could have a greater impact on this population. In turn, individual site fidelity could indicate low adaptability to environmental changes and could lead to potential carry-over effects. Annual migration data indicate that conservation planning must consider all sites used by such mobile species.

At-sea foraging behaviour in Hutton’s shearwater (Puffinus huttoni) as revealed by stable isotope analysis

Stable isotope analysis of feathers can provide an indirect method to investigate the diet and foraging locations of birds during the time the feathers were growing. We used the isotopic composition of experimentally-induced feathers to investigate the foraging locations of the Hutton’s shearwater (Puffinus huttoni), an endangered seabird that is a breeding endemic to the Kaikōura region of New Zealand. The isotopic composition of feathers was first compared with potential prey items collected from the near-shore marine environment near the breeding colony.

Can diet composition estimates using stable isotope analysis of feathers predict growth and condition in nestling mountain bluebirds (Sialia currucoides)?

Insectivorous birds breeding in seasonal environments provision their dependent young during periods when prey diversity and abundance vary. Consequently, the composition and nutritional value of diets parents feed to their offspring may differ within and among broods, potentially affecting the condition of nestlings. In a population of mountain bluebirds (Sialia currucoides), we used two methods to estimate diet composition for individual nestlings: direct observation of provisioning using video recordings at 5 and 9 days post‐hatch, and stable isotopes of the δ13C and δ15N in nestling feathers and prey followed by analysis with mixing models. We determined the macronutrient content (% fat and lean mass) and estimated the metabolized energy from each type of prey. We evaluated whether different methods of estimating diet composition would produce similar results, and whether the types of prey nestlings ate at one or both ages affected their morphology, growth rates, or blood ketone concentration. We found that bluebirds fed their young 5 main types of prey: beetles, cicadas, grasshoppers, insect larvae, and spiders. Both observational and mixing model estimates of diet composition indicated that larvae are traded off with grasshoppers and that fewer larvae are provided to nestlings as the season progresses. In evaluating how diet influences individual growth and condition, estimates from direct observations had greater explanatory power than those from mixing models, indicating that diets rich in the most energy‐dense prey (greatest fat content; cicadas and larvae) were associated with larger size and higher body condition, and faster rate of mass gain and growth of tarsus. Lower value prey had more limited, specific effects on nestlings, but may still be important dietary components. While isotopic methods produced estimates of diet composition that were generally informative, when applied to explain the growth and condition of nestlings they proved less useful.

Inter-annual variation in the trophic niche of Magellanic penguins Spheniscus magellanicus during the pre-molt period in the Beagle Channel

Inter-annual variations in the diets of seabirds are often a reflection of resource availability, with population dynamics and community structure implications. We investigated the trophic niche of Magellanic penguinsSpheniscus magellanicusduring the pre-molt stage in 6 years (2009 and 2013-2017) at Martillo Island, Beagle Channel, Argentina, using carbon and nitrogen stable isotope analysis of feathers. We found higher values in 2009 compared to the other years for both isotopes and estimated different proportions of prey in the diet of Magellanic penguins throughout the years. In 2009, penguins consumed mainly a mixture of benthic and benthopelagic fish, whereas from 2013 to 2017, the proportion of the pelagic form of squat lobsterMunida gregaria, considered a key species in the Beagle Channel, increased over time and nearly dominated diets in 2017. Our results confirm that Magellanic penguins act as sentinels, reflecting shifts in the marine community of the Beagle Channel via inter-annual variation in their trophic niche and diet composition.

Too salty for you? Changes of diet in the laughing gull nestlings during the growing period

In many seabird and waterbird species, salinity can impose physiological stress on recently hatched chicks because they have a limited capacity to excrete salt loads. In response, parents can select low‐salt food for their nestlings in the first stage of their growth. We determined the growth‐related variation in the diet of laughing gull Leucophaeus atricilla nestlings by using stable isotope analysis of feathers. Isotopic measurement of hatchling down reflects the mother's diet before laying eggs. At the same time, the primary feather tip indicates the food intake during the initiation of feather growth (one week of age), and the primary feather base indicates the food provided by parents during the period immediately before fledging. δ15N and δ13C values among the feather types showed a spatiotemporal shift in the nestlings’ diet. Younger chicks consumed more terrestrial prey sources (weevil beetles Sphenophorus sp.; ~51%) than chicks at fledging (~2%). However, fledging chicks and females before egg‐laying consumed mostly marine prey sources (Pacific white shrimp Litopenaeus vannamei and anchovy Anchoa sp.; > 90%). The base and primary tip portions had similar δ15N values, but both sections were less enriched than the hatchling down. This change was diet‐related, as the nestlings showed a lower percentage of anchovy consumption (13.3–14.7%) compared to females before egg‐laying (30.4%). Younger chicks had a different spatial niche than fledglings and females before egg‐laying, indicating a diet shift through the chick growth period. Assuming that the availability of food in the terrestrial or marine foraging areas did not vary through the nestlings’ growth period (five weeks), our findings support food resource selectivity by parents for their offspring during the first days of life, to reduce the physiological stress caused by high salt loads.

Long-term dietary shift and population decline of a pelagic seabird-A health check on the tropical Atlantic?

In the face of accelerating ecological change to the world's oceans, seabirds are some of the best bio-indicators of marine ecosystem function. However, unravelling ecological changes that pre-date modern monitoring programmes remains challenging. Using stable isotope analysis of feathers and regurgitants collected from sooty terns (Onychoprion fuscatus) nesting at a major Atlantic colony, we reconstructed a long-term dietary time series from 1890 to the present day and show that a significant dietary shift occurred during the second half of the twentieth century coinciding with an apparent population collapse of approximately 84%. After correcting for the "Suess Effect," δ13 C in feathers declined by ~1.5‰ and δ15 N by ~2‰ between the 1890s and the present day, indicating that birds changed their diets markedly over the period of population decline. Isotopic niches were equally wide before and after the population collapse but isotopic mixing models suggest that birds have grown ever more reliant on nutrient-poor squid and invertebrates as teleost fish have declined in availability. Given that sooty terns rely heavily on associations with sub-surface predators such as tuna to catch fish prey, the rapid expansion of industrialized fisheries for these species over the same period seems a plausible mechanism. Our results suggest that changes to marine ecosystems over the past 60years have had a dramatic impact on the ecology of the most abundant seabird of tropical oceans, and highlight the potentially pervasive consequences of large predatory fish depletion on marine ecosystem function.

Reconstructing Greater Sage-Grouse chick diets: Diet selection, body condition, and food availability at brood-rearing sites

ABSTRACTGrowth and survival of juvenile birds is nutritionally demanding, making the availability of major foods critical to population productivity. Access to nutritious foods for juveniles has important implications because poor foraging conditions during development could result in mortality, or reduced fitness in adulthood. Selection of brood-rearing habitats by female Greater Sage-Grouse (Centrocercus urophasianus) thus has broad implications to survival of juveniles and persistence of populations. Previous research using crop contents demonstrated that invertebrates and forbs comprise the major portion of sage-grouse chick diets for the first few months post-hatch. We coupled stable isotope analysis of feathers and field measurements to quantify chick diet and then correlated that with measures of chick body condition. We sought to reconstruct sage-grouse chick dietary history (2013–2015) using nitrogen stable isotopes to (1) evaluate whether selection of brood-rearing habitats by female sage-grouse was related to chick diet, and (2) assess the relationship between dietary consumption and body condition. Brood-rearing females selected habitats in areas where diet resources occurred in proportion to their availability, with the exception that females selected areas with greater forb abundance 4 weeks after hatch. Diet assimilation by chicks at brood-rearing locations was unrelated to the availability of forbs and invertebrates, but consumption of forbs increased with chick age. Chicks that assimilated proportionally greater amounts of plant-derived nitrogen in their feathers during their first week of life tended to weigh more and have longer wing chords. This relationship was similar between male and female chicks. The importance of quality foods for sage-grouse is well recognized and conservation efforts should aim to maintain functioning sagebrush ecosystems containing adequate brood-rearing habitats for juvenile sage-grouse; there remains a need to identify whether desirable effects are achievable when attempting to improve big sagebrush (Artemisia tridentata) habitats to benefit sage-grouse populations.

The gut of the finch: uniqueness of the gut microbiome of the Gal\xe1pagos vampire finch

BackgroundDarwin’s finches are a clade of 19 species of passerine birds native to the Galápagos Islands, whose biogeography, specialized beak morphologies, and dietary choices—ranging from seeds to blood—make them a classic example of adaptive radiation. While these iconic birds have been intensely studied, the composition of their gut microbiome and the factors influencing it, including host species, diet, and biogeography, has not yet been explored.ResultsWe characterized the microbial community associated with 12 species of Darwin’s finches using high-throughput 16S rRNA sequencing of fecal samples from 114 individuals across nine islands, including the unusual blood-feeding vampire finch (Geospiza septentrionalis) from Darwin and Wolf Islands. The phylum-level core gut microbiome for Darwin’s finches included the Firmicutes, Gammaproteobacteria, and Actinobacteria, with members of the Bacteroidetes at conspicuously low abundance. The gut microbiome was surprisingly well conserved across the diversity of finch species, with one exception—the vampire finch—which harbored bacteria that were either absent or extremely rare in other finches, including Fusobacterium, Cetobacterium, Ureaplasma, Mucispirillum, Campylobacter, and various members of the Clostridia—bacteria known from the guts of carnivorous birds and reptiles. Complementary stable isotope analysis of feathers revealed exceptionally high δ15N isotope values in the vampire finch, resembling top marine predators. The Galápagos archipelago is also known for extreme wet and dry seasons, and we observed a significant seasonal shift in the gut microbial community of five additional finch species sampled during both seasons.ConclusionsThis study demonstrates the overall conservatism of the finch gut microbiome over short (< 1 Ma) divergence timescales, except in the most extreme case of dietary specialization, and elevates the evolutionary importance of seasonal shifts in driving not only species adaptation, but also gut microbiome composition.

Flyway population delineation in Taiga Bean Geese Anser fabalis fabalis revealed by multi‐element feather stable isotope analysis

Fundamental to effective management of migratory waterbird populations is an understanding of their flyway delineation. Taiga Bean Geese Anser fabalis fabalis wintering in NW Denmark, Scotland and England are considered to originate from northern and central Sweden, southern and central Norway (‘Western flyway’), those wintering in southern Sweden, NE and southern Denmark are considered to originate from northern Fennoscandia and western Russia (‘Central flyway’), and those wintering in eastern Germany and Poland (which show far less favourable conservation status) are thought to come from western Siberia (‘Eastern 1 flyway’), although evidence to demonstrate this has largely been lacking. Evidence for different natal and moult origins of Taiga Bean Geese was investigated using stable isotope analyses of feathers of four elements (δ2H, δ13C, δ15N and δ34S). There were significant differences in isotopic composition of feathers from Swedish (Central) and German (Eastern 1) wintering populations and those moulting in Sweden in late summer (Western), which validated the three proposed major management flyway units above. The strong continental gradient in the stable hydrogen isotope ratios in precipitation (δ2Hp) across the region was used to assign wintering birds geospatially to natal and moulting origin, indicating separate natal and moulting areas for German (n = 37, from western Siberia) and Swedish (n = 20, Fennoscandia and more western Russia) wintering birds. These results confirm the largely discrete nature of these three flyways and contribute significantly to our ability to deliver effective targeted and appropriate research, monitoring and management actions throughout the ranges of these flyways.

Breeding origin and spatial distribution of migrant and resident harriers in a Mediterranean wintering area: insights from isotopic analyses, ring recoveries and species distribution modelling

Variation in avian migratory behaviour is widespread, not only among species but also within species, and can involve shifts from sedentary at low latitudes to migratory at high latitudes. This leads to a situation whereby non-migratory populations of a species at lower latitudes are periodically joined by migratory conspecifics during winter. Determining spatio-temporal dynamics in distribution and structure of different populations is crucial to our understanding of their ecology and interactions, but it is often difficult or impossible to separate resident from migrant populations. Here, we used the winter distribution of Marsh Harrier (Circus aeruginosus) in the Iberian Peninsula (southwest Europe) to analyse the potential of spatial distribution models and stable isotope analyses of feathers (deuterium, δ2H) to evaluate differences in spatial distribution of migrant and resident raptor populations in southern Europe. Overall, ring recoveries and isotopic assignment showed that most migrant harriers wintering in the Iberian Peninsula had a central and northern latitudinal European origin. Our results revealed segregation in the winter distribution of migrant and resident Marsh Harrier populations in the Iberian Peninsula. These results have important conservation implications, suggesting that ecological conditions and potential stressors could greatly differ among resident and migrant populations in winter. Our approach provided a useful methodological procedure to evaluate the wintering spatial segregation of European populations of a raptor species and presents a new challenge to the study of their ecological consequences.

The status and ecology of the last wild population of Madagascar Pochard Aythya innotata

SummaryOne of the rarest birds in the world, the Madagascar Pochard Aythya innotata was thought to be extinct until a small population was found in 2006. Little is known about this diving duck as it had not been studied prior to its decline and disappearance. Its rediscovery provided the opportunity to study this species in the wild for the first time and to assess the viability of this last remaining population. The population is small, fluctuating around 25 individuals, and mainly utilises two small volcanic lakes in the far north of Madagascar. Nesting occurs on only one of these lakes, Matsaborimena. Nest success (76% in 2007–2008) and hatching success (89% in 2007–2008) are both comparable to other Aythya species, but fledging success (4% in 2011–2012) is extremely low. Duckling mortality rates peak between 14 and 21 days old. We propose that starvation is the major cause of duckling mortality. Examination of faecal samples and stable isotope analysis of feathers and potential food items provide evidence that adult pochards are insectivorous, favouring caddis fly larvae. Macroinvertebrate density in the benthos of Matsaborimena is low. Adults spend 38% of daylight hours foraging, mainly in the shallowest water. However Matsaborimena is steep-sided and has no areas shallow enough for diving ducklings to feed. We conclude that these lakes are not good breeding habitat for this species. The Madagascar Pochard’s persistence here and not at other sites is probably due to a lack of the human-induced habitat degradation that has impacted many other wetlands in Madagascar.

GREAT SHEARWATER(PUFFINUS GRAVIS) MORTALITY EVENTS ALONG THE EASTERN COAST OF THE UNITED STATES

The Great Shearwater (Puffinus gravis) is an abundant pelagic seabird that undertakes transequatorial migrations between the North and South Atlantic Ocean. This species is a useful indicator of large-scale alterations in marine dynamics due to its wide geographic range, long-distance migrations, and relative abundance. From 1993 to 2011, 12 separate mortality events, with 4,961 Great Shearwaters recovered, were documented along the eastern coast of the United States. Of these, seven events (n=4,885) occurred in the Southeast (SE) and five (n=76) in the Northeast (NE) United States. The cause of death was determined either by necropsy (n=60) or external examination (n=4,901). All Great Shearwaters stranded along the SE United States were emaciated while 58% were emaciated in the NE United States. No plastic was observed in Great Shearwaters in the SE US (n=27), but the gastrointestinal tract of 82% (n=27) of all stranded birds along the NE United States had at least one plastic bead. There was no evidence of infectious disease or heavy metals in stranded Great Shearwaters examined (n=14, from the 2005 SE event). Stable isotope analysis of feathers (n=9, from a 2007 SE event) suggests dietary differences between emaciated stranded birds and live-caught healthy birds. The temporal distribution of stranding detections suggests a general increase in the number of observed Great Shearwater strandings over the past two decades. From 1993 to 2000 there were a total of three mortality events with 296 individual Great Shearwaters. However, there was a threefold increase in the number of mortality events from 2001 to 2011 (nine events involving 4,665 individuals). The causes of this apparent increase in strandings are unknown but may be due to an increase in reporting effort over the past two decades combined with changing oceanographic conditions in the South Atlantic Ocean, leading to large-scale mortality of emaciated Great Shearwaters along the east coast of the United States.

Feeding ecology and movements of the Barolo shearwater Puffinus baroli baroli in the Azores, NE Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 452:269-285 (2012) - DOI: https://doi.org/10.3354/meps09670 Feeding ecology and movements of the Barolo shearwater Puffinus baroli baroli in the Azores, NE Atlantic Verónica C. Neves1,*, Joël Bried1, Jacob González-Solís2, Jose L. Roscales2,3, Malcolm R. Clarke4 1Departamento de Oceanografia e Pescas, Centro do IMAR da Universidade dos Açores, Rua Frederico Machado n°4, 9901-862 Horta, Faial, Azores, Portugal 2Institut de Recerca de la Biodiversitat (IRBio) and Departament de Biologia Animal, Universitat de Barcelona, Avenida Diagonal 645, 08028 Barcelona, Spain 3Departamento de Análisis Instrumental y Química Ambiental, Instituto de Química Orgánica general (IQOG-CSIC), Calle Juan de la Cierva 3, 28006 Madrid, Spain 4Rua do Porto 18, 9930-430 Lajes do Pico, Azores, Portugal *Email: neves_veronica@yahoo.com ABSTRACT: Trophic ecology and movements are critical issues for understanding the role of marine predators in food webs and for facing the challenges of their conservation. Seabird foraging ecology has been increasingly studied, but small elusive species, such as those forming the ‘little shearwater’ complex, remain poorly known. We present the first study on the movements and feeding ecology of the Barolo shearwater Puffinus baroli baroli in a colony from the Azores archipelago (NE Atlantic), combining global location-sensing units, stable isotope analyses of feathers (δ13C and δ15N), stomach flushings and data from maximum depth gauges. During the chick-rearing period, parents visited their nests most nights, foraged mainly south of the colony and fed at lower trophic levels than during the non-breeding period. Squid was the most diverse prey (6 families and at least 10 different taxa), but species composition varied considerably between years. Two squid families, Onychoteuthidae and Argonautidae, and the fish family Phycidae accounted for 82.3% of ingested prey by number. On average, maximum dive depths per foraging trip reached 14.8 m (range: 7.9 to 23.1 m). After the breeding period, birds dispersed offshore in all directions and up to 2500 km from the breeding colony, and fed at higher trophic levels. Overall, our results indicate that the Barolo shearwater is a non-migratory shearwater feeding at the lowest trophic level among Macaronesian seabirds, showing both diurnal and nocturnal activity and feeding deeper in the water column, principally on small schooling squid and fish. These traits contrast with those of 3 other Azorean Procellariiformes (Cory’s shearwater Calonectris diomedea, the Madeiran storm-petrel Oceanodroma castro and Monteiro’s storm-petrel O. monteiroi), indicating ecological segregation within the Azorean seabird community. KEY WORDS: Barolo shearwater · Puffinus baroli baroli · Diet · Foraging behaviour · Stable isotopes · Activity patterns · At-sea distribution · North-eastern Atlantic Full text in pdf format PreviousNextCite this article as: Neves VC, Bried J, González-Solís J, Roscales JL, Clarke MR (2012) Feeding ecology and movements of the Barolo shearwater Puffinus baroli baroli in the Azores, NE Atlantic. Mar Ecol Prog Ser 452:269-285. https://doi.org/10.3354/meps09670 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 452. Online publication date: April 25, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Different Means to the Same End: Long-Distance Migrant Seabirds from Two Colonies Differ in Behaviour, Despite Common Wintering Grounds

Although seabirds that are trans-equatorial migrants show apparently broad overlap among populations in the non-breeding season, such large-scale pattern may conceal subtle but nevertheless key differences in migratory behaviour. These specializations could reflect adaptation to different environments during the breeding season, carry-over effects from the breeding to the nonbreeding period, or asymmetries in competitive ability of birds of different origin. We compared the migratory and wintering behaviour of Cory's shearwaters Calonectris diomedea nesting in Berlengas and in the Selvagens, two colonies in contrasting oceanographic environments, separated by ca. 1200 km. Although no differences were found in winter distribution, there was a marked divergence in timing, route and the use of staging areas during the postbreeding (autumn) migration. Birds from Berlengas typically travelled to oceanic waters in the North Atlantic for an extended stopover, whereas those from Selvagens rarely did so. In the South Atlantic, birds from Selvagens spent more time in flight, perhaps because they had higher energy and nutrient requirements for feather replacement compared to birds from Berlengas, which moult more flight feathers during breeding. Stable isotope analyses of feathers suggested that this variation in activity patterns was unrelated to trophic ecology. Differences in migration routes and stopovers may expose populations to distinct threats, and should be taken into consideration when defining units for conservation purposes and developing appropriate management strategies.

Combining stable isotope analyses and geolocation to reveal kittiwake migration

Determining migratory strategies of seabirds is still a major challenge due to their relative inaccessibility. Small geolocators are improving this knowledge, but not all birds can be tracked. Stable isotope ratios in feathers can help us to understand migration, but we still have insufficient baseline knowledge for linking feather signatures to movements amongst distinct water masses. To understand the migration strategies of kittiwakes Rissa tridactyla and the link between stable isotopes in feathers and the areas in which these were grown, we tracked 6 kittiwakes from Hornoya, Norway, with light level geolocators over 1 yr. Then we analysed the stable isotopes of carbon and nitrogen in their 1st and 7th primary feathers as well as in the 1st, 3rd, 5th, 7th and 10th primaries of 12 birds found freshly dead in the same breeding colony. After breeding, all tracked birds moved east of the Svalbard Archipelago and subsequently migrated to the Labrador Sea. Thereafter, birds showed individual variation in migration strategies: 3 travelled to the NE Atlantic, whereas the others remained in the Labrador Sea until the end of the wintering period. Changes in stable isotope signatures from the 1st to the 10th primary feathers corresponded well to the sequence of movements during migration and the area in which we inferred that each feather was grown. Thus, by combining information on moult patterns and tracking data, we demonstrate that stable isotope analysis of feathers can be used to trace migratory movements of seabirds.

High variation reduces the value of feather stable isotope ratios in identifying new wintering areas for aquatic warblers Acrocephalus paludicola in West Africa

Stable isotope analysis of feathers can be useful in the study of seasonal interactions and migratory connectivity in birds. For the PalaearcticAfrican migration system, however, the lack of isotope data from feathers of known origin in Africa renders the geographic assignment of birds captured on European breeding grounds to potential wintering areas problematic. Rectrices of the threatened aquatic warbler Acrocephalus paludicola grown in Africa were sampled across six European countries to assess whether birds in different breeding populations shared similar isotopic signatures and so were likely to have wintered in the same region in Africa. Freshly grown feathers of aquatic warblers collected at the only known wintering site in Senegal showed high variation in carbon, nitrogen, and hydrogen isotope ratios. Due to similarly high variation in isotope ratios of African-grown feathers within all breeding populations, it was not possible to determine whether different populations wintered in different regions. However, isotope signatures of 20% of birds captured on European breeding grounds fell outside the range of those captured in Senegal, suggesting a wider wintering distribution than is currently known. We therefore assessed whether the origin of these feathers could be estimated by trying to establish isotopic gradients across sub-Saharan West Africa. Feathers of three ecologically similar surrogate species were sampled from wetlands across a 3000 km east-west and a 2000 km northsouth transect. Within-site variation in feather isotope ratios was frequently larger than the difference predicted by gradients across West Africa. Thus, predicting the origin of individual feathers using single-isotope gradients was not reliable. The large within-site variability of feather isotope ratios of a habitat specialist species like the aquatic warbler indicates that using feather isotope ratios will require large sample sizes from many locations, and may thus not be an efficient tool in identifying wintering areas of Palaearctic African migrants.

Variation in deuterium (δD) signatures of Yellow Warbler Dendroica petechia feathers grown on breeding and wintering grounds

Stable isotope analysis of feathers may help track populations of migratory birds throughout their annual cycle. We use deuterium isotope ratios in feathers (δDf) to confirm that Yellow Warblers Dendroica petechia go through both a prebasic molt on or near their breeding grounds and a prealternate molt on their wintering grounds, and evaluate whether δD analysis of different feather types can help assign birds to breeding and winter origins. We show that primary coverts and tail feathers have δDf values that reflect long-term average deuterium isotope ratios in precipitation (δDP) on the breeding grounds. Most greater coverts and crown feathers, however, have δDf values that are more enriched than predicted based on the δDP of their wintering distribution. We also found significant interannual variation in the δDf values of tail feathers, greater coverts and crown feathers. Interannual variation in δDf of winter-grown feathers may be explained by El Nino/La Nina conditions that influence rainfall and thus δDP; feathers were more depleted following an El Nino year (2005) than a La Nina year (2006). Gender had no effect on the δDf values of any feathers sampled. Age influenced the δDf values of crown feathers but not greater coverts. This study therefore confirms that δDf of summer-grown feathers can be used to identify breeding locations, but suggests that the ability to use δDf of winter-grown feathers to assign individuals to winter locations is limited by weak spatial gradients and temporal variation in δDP.

Altitudinal migration in American Dippers (Cinclus mexicanus): Do migrants produce higher quality offspring?

Breeding at high elevations can favour life-history strategies in which parents shift to investing in higher quality rather than higher numbers of offspring. In American Dippers ( Cinclus mexicanus Swainson, 1827), altitudinal migrants produce fewer fledglings than sedentary individuals (residents) that breed at lower elevations. We examined whether migrants compensate for their lower fecundity by providing their offspring with a higher quality diet and (or) more food, and producing higher quality offspring. Nestling diet was assessed using observations and stable isotope analysis of feathers grown during the nestling period. Nestling quality was assessed using a condition index (residuals from a mass–tarsus regression) and postfledging survival. We found that migrants fed their offspring less fish, and despite having higher feeding rates, had lower energetic provisioning rates than residents. Migrants also produced offspring that were in worse condition and had lower postfledging survival. This study found no evidence that altitudinal migration is associated with a trade-off favouring the production of smaller numbers of higher quality young. Instead our data provide support for the hypothesis that altitudinal migration in American Dippers is an outcome of competition for limited nest sites at lower elevations that forces some individuals to move to higher elevations to breed.

Goats, birds, and emergent diseases: apparent and hidden effects of exotic species in an island environment

Exotic species can have devastating effects on recipient environments and even lead to the outbreak of emergent diseases. We present here several hidden effects that the introduction of goats has had on the Lesser Short-toed Lark, Calandrella rufescens, the commonest native bird inhabiting the island of Fuerteventura (Canary Islands). Vegetation structure varied with grazing pressure, and indeed, vegetation was all but eradicated from the locality with greatest goat densities, which was also where the lowest density of Lesser Short-toed Larks was recorded. The impact of habitat impoverishment, however, was partially compensated for by changes in the foraging behavior of birds, which benefited from the abundant food provided to goats on farms. Capture-resighting methods showed that birds visiting farms outnumbered the estimates for birds obtained in the surrounding natural habitat, suggesting that there was recruitment from a much larger area. Stable isotope analyses of feathers indicated that island birds feed largely on the maize supplied at goat farms, showing poorer body condition than birds from populations not associated with farms (peninsular Spain and Morocco). Moreover, larks from Fuerteventura had a very high prevalence of poxvirus lesions compared with other bird populations worldwide and may increase the risk of contracting the disease by feeding on farms, where they aggregate and coexist atypically with domestic birds. The island birds also had lower average productivity, which may be the consequence of the emergent disease and/or the poor nutritional state resulting from feeding on a low-protein diet. Diseased and non-diseased birds from Fuerteventura showed similar body condition and annual survival rates. However, the isotopic traces of delta 13C indicate that the diet of diseased birds was more uniform than that of non-diseased birds, being based on food from goat farms. Our results show how the combination of species frequently introduced onto islands (goats, poultry, and associated pathogens) can create ecological traps for native species that are not always easy to identify. Moreover, we stress that nutrition and infectious diseases are important determinants of the well-being and dynamics of animal populations, and thus health research must be included in the design of monitoring programs and conservation strategies.