Keith Hobson - Academia.edu (original) (raw)

Papers by Keith Hobson

Movement Ecology

Aerial insectivorous birds have suffered steep population declines in North America over the last... more Aerial insectivorous birds have suffered steep population declines in North America over the last 60 years. A lack of information on migratory connectivity between breeding and non-breeding grounds for these species limits our ability to interpret factors affecting their population-specific trends. We determined likely Latin American non-breeding regions of Bank (Riparia riparia), Barn (Hirundo rustica) and Cliff (Petrochelidon pyrrhonota) swallow from populations across their breeding ranges. We used predicted feather hydrogen (δ2Hf) and carbon (δ13Cf) isoscapes for winter-grown feathers to indicate areas of highest probability of moult origin and incorporated these results into a cluster analysis to determine likely broad non-breeding regions. We also assessed variation in wing length among populations to determine the potential for this metric to differentiate population moult origins. We then investigated patterns of multi-isotopic (δ2Hf, δ13Cf, δ15Nf) and wing-length niche occu...

Frontiers in Ecology and Evolution

IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is on... more IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is one of the most iconic, whose journey is fueled by nectar from flowering plants along the migratory route which may involve up to 3,500 km. Understanding how and where monarchs obtain their dietary resources to fuel migratory flight and ensure overwintering stores would provide new insights into the migratory strategy of this species and subsequently help focus conservation efforts.MethodsThis pilot study was designed as a first attempt to assess the composition, dynamics, and isotopic (δ2H, δ13C) composition of essential and non-essential fatty acids (FA) acquired or manufactured de novo from larval host milkweed (Asclepias spp.) by monarch butterflies and from adult emergence to overwintering.ResultsData from controlled laboratory isotopic tracer tests suggested that adult monarchs convert their dietary energy mainly into 16:0 and 18:1 fatty acids and store them as neutral lipids in thei...

Ibis

The Iberian and North African populations of reed warblers have been described recently as a sepa... more The Iberian and North African populations of reed warblers have been described recently as a separate taxon, ambiguus, forming a sister clade to the Sahelian subspecies minor of African Reed Warbler Acrocephalus baeticatus. Although the breeding range of ambiguus has been identified, the migration strategy of its populations remained unknown. We deployed geolocators and sampled the innermost primary from breeding adults in Spain for stable hydrogen (δ2H) analyses and also analysed stable carbon (δ13C) and nitrogen (δ15N) isotopes in feathers collected in two reed warbler taxa (Acrocephalus scirpaceus and Acrocephalus baeticatus ambiguus) in Morocco, to identify the moulting and wintering sites of these populations. Ring recoveries, geolocator tracks and probabilistic assignments to origin from δ2H values indicate that Spanish ambiguus are likely to moult south of the Sahara and winter in West Africa, probably from Mauretania to southern Mali and Ivory Coast. Moroccan ambiguus, howev...

European Journal of Wildlife Research, 2022

Conservation of migratory birds requires knowledge of breeding and nonbreeding ranges and the con... more Conservation of migratory birds requires knowledge of breeding and nonbreeding ranges and the connections between them. European turtle doves (Streptopelia turtur) are Palearctic-African long-distance migrants with wintering areas in the Sub-Saharan belt that are classed as vulnerable due to strong population declines. However, detailed non-breeding locations of individuals from different migratory flyways are unknown. To identify wintering regions of turtle doves, we measured stable isotopes of feathers grown on the wintering grounds and used a dual-isotope (hydrogen (δ2Hf) and carbon (δ13Cf)) probabilistic assignment to analyse origins of individuals migrating through the western and central/eastern flyways. The most probable wintering areas for turtle dove samples from both flyways were in the western and central Sub-Sahara. However, we found differences in δ2Hf and δ13Cf values between turtle doves following different migratory routes (western vs central/eastern flyway). This re...

Ornithology, 2021

Identifying the composition of avian diets is a critical step in characterizing the roles of bird... more Identifying the composition of avian diets is a critical step in characterizing the roles of birds within ecosystems. However, because birds are a diverse taxonomic group with equally diverse dietary habits, gaining an accurate and thorough understanding of avian diet can be difficult. In addition to overcoming the inherent difficulties of studying birds, the field is advancing rapidly, and researchers are challenged with a myriad of methods to study avian diet, a task that has only become more difficult with the introduction of laboratory techniques to dietary studies. Because methodology drives inference, it is important that researchers are aware of the capabilities and limitations of each method to ensure the results of their study are interpreted correctly. However, few reviews exist which detail each of the traditional and laboratory techniques used in dietary studies, with even fewer framing these methods through a bird-specific lens. Here, we discuss the strengths and limita...

Scientific Reports, 2021

Naturally occurring stable isotope ratios in animal tissues allow estimation of species trophic p... more Naturally occurring stable isotope ratios in animal tissues allow estimation of species trophic position and ecological niche. Measuring multiple isotopes of migratory species along flyway bottlenecks offers the opportunity to sample multiple populations and species whose tissues carry information at continental scales. We measured δ2H, δ18O, δ13C, δ15N in juvenile feathers of 21 bird species captured at a migratory bottleneck in the Italian Alps. We examined if trends in individual isotopes reflected known migratory strategies and whether dietary (δ13C–δ15N) and spatially-explicit breeding origin (δ2H–δ18O) niche breadth (NB) differed among long-distance trans-Saharan (TS), short-distance (IP) and irruptive (IR) intra-Palearctic migrants, and whether they correlated with reported populations long-term trends. In both TS and IP groups, species δ2H declined with capture date, indicating that northern populations reached the stopover site later in the season, following a Type-I migrat...

Global Ecology and Conservation, 2020

Global Ecology and Conservation 24 (2020) e01346 snowfinches, there is a risk of increased isolat... more Global Ecology and Conservation 24 (2020) e01346 snowfinches, there is a risk of increased isolation of the southern populations under a scenario of global warming, insofar as the hypothetical settling of winter immigrants could no longer contribute to a demo-genetic rescue. Future research should decipher how these risks affect alpine species that are particularly exposed to climatic shifts, and how they adapt and evolve.

Science of The Total Environment, 2021

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The Auk, 2019

Carry-over effects from one stage of the annual cycle to subsequent stages can have profound effe... more Carry-over effects from one stage of the annual cycle to subsequent stages can have profound effects on individual fitness. In migratory birds, much research has been devoted to examining such effects from the nonbreeding to the breeding period. We investigated potential carry-over effects influencing spring body condition, breeding phenology, and performance for 3 species of sympatric, declining Nearctic–Neotropical migratory swallows: Bank Swallow (Riparia riparia), Barn Swallow (Hirundo rustica), and Cliff Swallow (Petrochelidon pyrrhonota). To examine carry-over effects, we used structural equation modeling and several intrinsic markers, including stable isotope (δ 2H, δ 13C, and δ 15N) and corticosterone (CORTf) values from winter molted-feathers, and changes in telomere length between breeding seasons. We found support for carry-over effects for all 3 species, however, the specific relationships varied between species and sexes. Effects leading to lower breeding performance we...

Ecology and Evolution, 2019

Migration can influence host–parasite dynamics in animals by increasing exposure to parasites, by... more 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 (δ2Hf) 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 Haem...

Scientific Reports, 2019

Wide-ranging apex predators are among the most challenging of all fauna to conserve and manage. T... more Wide-ranging apex predators are among the most challenging of all fauna to conserve and manage. This is especially true of the polar bear (Ursus maritimus), an iconic predator that is hunted in Canada and threatened by global climate change. We used combinations of stable isotopes (13C,15N,2H,18O) in polar bear hair from > 1000 individuals, sampled from across much of the Canadian Arctic and sub-Arctic, to test the ability of stable isotopic profiles to ‘assign’ bears to (1) predefined managed subpopulations, (2) subpopulations defined by similarities in stable isotope values using quadratic discriminant analysis, and (3) spatially explicit, isotopically distinct clusters derived from interpolated (i.e. ‘kriged’) isotopic landscapes, or ‘isoscapes’, using the partitioning around medoids algorithm. A four-isotope solution provided the highest overall assignment accuracies (~80%) to pre-existing management subpopulations with accuracy rates ranging from ~30–99% (median = 64%). Assi...

Journal of Ornithology, 2019

By analysing deuterium concentration in scapulars and in rectrices (δ 2 Hf) of breeding and sprin... more By analysing deuterium concentration in scapulars and in rectrices (δ 2 Hf) of breeding and spring migrating Ortolan Buntings (Emberiza hortulana), we found a high correlation attesting that spring body and central rectrices have grown in similar isotopic environments. Furthermore, we failed to find a correlation between δ 2 Hf of rectrices and amount-weighted growing season precipitation δ 2 Hp of sites where we captured the birds. Winter grown body coverts and rectrices displayed similar probabilistic assignments to origin. Further examination of 76 tails of breeding birds captured in Finland in May-June confirmed that breeding birds wear recently moulted central rectrices. The body coverts are known to moult during the winter partial moult in that species, but the rectrices were reported to moult only once a year, during the complete post breeding moult occurring on the breeding grounds in summer. Here we reveal the common replacement of the central pair in winter too. The winter tail moult could occur beyond the central pair in some individuals, but this has still to be confirmed or refuted, by e.g. further isotopic investigations.

Science Advances, 2019

Targeting bird migration connectivity adressed a pressing conservation policy question to save or... more Targeting bird migration connectivity adressed a pressing conservation policy question to save ortolan buntings.

Ecosphere, 2019

Natal and breeding dispersal represents an important component of animal demography and metapopul... more Natal and breeding dispersal represents an important component of animal demography and metapopulation theory. This phenomenon also has implications for conservation and management because understanding movements of individuals potentially allows the identification of key habitats that may be acting as population sources or sinks. Intrinsic markers such as stable isotope abundance in tissues that can be associated with provenance can provide a coarse but pragmatic solution to understanding such movements. Different methodologies have been proposed to quantify natal and breeding dispersal by using stable isotope analyses of keratinous tissues (hair, feathers), each of them with their own advantages and limitations. Here, we compared results provided by four different methods to estimate dispersal (three already published and one novel) in animals using stable isotope measurements. We used a single large dataset of feather δ2H values from golden‐winged warblers (Vermivora chrysoptera)...

Ecology Letters, 2018

Environmental change induces some wildlife populations to shift from migratory to resident behavi... more Environmental change induces some wildlife populations to shift from migratory to resident behaviours. Newly formed resident populations could influence the health and behaviour of remaining migrants. We investigated migrant-resident interactions among monarch butterflies and consequences for life history and parasitism. Eastern North American monarchs migrate annually to Mexico, but some now breed year-round on exotic milkweed in the southern US and experience high infection prevalence of protozoan parasites. Using stable isotopes (d 2 H, d 13 C) and cardenolide profiles to estimate natal origins, we show that migrant and resident monarchs overlap during fall and spring migration. Migrants at sites with residents were 13 times more likely to have infections and three times more likely to be reproductive (outside normal breeding season) compared to other migrants. Exotic milkweed might either attract migrants that are already infected or reproductive, or alternatively, induce these states. Increased migrant-resident interactions could affect monarch parasitism, migratory success and long-term conservation.

Animal Migration, 2018

Stopovers used by birds during migration concentrate individuals from broad geographic areas pote... more Stopovers used by birds during migration concentrate individuals from broad geographic areas potentially providing important information on catchment areas of birds moving through these sites. We combined stable isotope (δ2H), genetic fingerprinting and band recovery data to delineate the molt origins of Wilson’s Warblers (Cardellina pusilla) migrating through a stopover site in southwestern Canada in the fall. We assessed changes in δ2Hf indicating latitudinal origins with ordinal date to show this species likely underwent leapfrog migration through this site. Using the combined approach to determine origins, Wilson’s Warblers migrating through southwestern Alberta in 2015 were mostly from the western boreal population (n = 155, 96%) with some individuals from the Pacific Northwest (n = 1, 0.6%), Rocky Mountain (n = 2, 1.2%) and eastern boreal (n = 3, 1.8%) populations. Our results suggest that individuals migrating through our study site come from a broad catchment area potentiall...

Scientific reports, Jan 22, 2017

Previous studies have linked winter habitat with subsequent breeding phenology and physical condi... more Previous studies have linked winter habitat with subsequent breeding phenology and physical condition of migratory birds, but few have found delayed effects of winter habitat on subsequent reproductive success. The aim of this study was to test if African winter habitat is related to subsequent reproductive success of house martins (Delichon urbicum) breeding at a colony in Spain. We measured stable isotope (δH, δC, δN) values from feathers moulted in West Africa and used confirmatory path analysis to test if isotopic values of winter-grown feathers were related to reproductive success through the mediation of breeding phenology and body condition. We conducted separate analyses for males, females and age classes (yearlings vs ≥ 2 years old). Experienced males wintering in habitats of higher rainfall (as inferred from lower feather δH values) were in better body condition and produced more offspring during the subsequent breeding season. In contrast, we did not find any effect of wi...

Journal of Ornithology, 2016

The population structure and seasonal movements of alpine birds in Europe are still largely unkno... more The population structure and seasonal movements of alpine birds in Europe are still largely unknown. Species living in high mountains now face acute risks of habitat loss, range contractions and local extinction due to current and projected climate change. Therefore, a better understanding of the spatial structuring and exchange among populations of European mountain birds is important from both ecological and conservation points of view. The White-winged Snowfinch Montifringilla nivalis is one of the most characteristic passerines of alpine habitats in Europe. Despite the fact that its breeding nuclei are relatively well defined, we still know little about the species' population structure and movements in Western Europe. By analysing two mitochondrial loci (cytochrome b and the control region) and stable isotopes of hydrogen (d 2 H), we assessed to what extent breeding populations of Whitewinged Snowfinches in the Cantabrian Mountains (CM), the Pyrenees and the Alps, and also a wintering population in the Eastern Pyrenees, function as a metapopulation. We first show the phylogenetic relationships of the Whitewinged Snowfinch (Montifringilla nivalis subsp. nivalis) within the Snowfinch complex. When assessing the population structure in Western Europe, most mitochondrial haplotypes were present in all breeding populations, but one was only found in the CM where it predominated. The most widespread haplotypes at the breeding grounds were found in the majority of the wintering individuals, but none of them showed the haplotype specific to the CM. We did not find differences in d 2 H for the primary feathers among breeding populations, but rectrices of individuals wintering in the Pyrenees had considerably lower d 2 H values: isotopic analysis could thus be useful to assign wintering birds to their Alpine breeding grounds. Further studies combining ringing and the analyses of intrinsic markers are an essential step in better appraising the species' metapopulation dynamics and guiding conservation. Keywords Alpine environments Á Bird ringing Á Intrinsic markers Á Migration Á Population dynamics Communicated by M. Wink.

Canadian Journal of Zoology, 2017

The Saskatchewan River Delta (SRD) is North America’s largest inland delta and an important stopo... more The Saskatchewan River Delta (SRD) is North America’s largest inland delta and an important stopover site for waterfowl in the Central Flyway. However, little is known about their basic feeding ecology at this site and how species segregate or overlap in resource use. We used stable carbon (δ13C) and nitrogen (δ15N) isotopes and mercury concentrations ([Hg]) in liver tissue to trace use of local nutrient sources by five waterfowl species and tested for differences in diets among species, sexes, and age groups. Macrophytes were the dominant food source for Northern Pintail (Anas acuta L., 1758) and American Wigeon (Anas americana Gmelin, 1789) with median proportions of 0.86 and 0.98, respectively. There was also evidence of partitioning of resources, as Blue-winged Teal (Anas discors L., 1766) and Green-winged Teal (Anas carolinensis Gmelin, 1789) consumed invertebrates, as did a subset of Mallards (Anas platyrhynchos L., 1758), suggesting that these birds might minimize competition...