Showing papers by "Keith A. Hobson published in 2004"
TL;DR: Stable isotope patterns in nature are reviewed and recent tracking applications in a range of taxa are discussed and a series of key issues and assumptions are discussed to aid in the interpretation and design of effective and insightful isotope movement studies.
Abstract: Establishing patterns of movement of wild animals is crucial for our understanding of their ecology, life history and behavior, and is a prerequisite for their effective conservation. Advances in the use of stable isotope markers make it possible to track a diversity of animal species in a variety of habitats. This approach is revolutionizing the way in which we make connections between phases of the annual cycle of migratory animals. However, researchers must exercise care in their application of isotopic methods. Here, we review stable isotope patterns in nature and discuss recent tracking applications in a range of taxa. To aid in the interpretation and design of effective and insightful isotope movement studies, we discuss a series of key issues and assumptions. This exciting field will advance rapidly if researchers consider these aspects of study design and interpretation carefully.
805 citations
TL;DR: This study reveals that δD measurements of feathers from migratory birds in Europe may be used to track their origin and movements, and so provide a powerful investigative tool for avian migration research in Europe.
Abstract: Successful application of stable-hydrogen iso- tope measurements (δDf) of feathers to track origins of migratory birds and other wildlife requires a fundamental understanding of the correlation between δDf and deute- rium patterns in rainfall (δDp) over continental scales. A strong correlation between δDp and δDf has been confirmed for birds and insects in North America, but not yet for other continents. Here, we compare δDf data from resident European birds to new δDp basemaps for Europe. Three maps, representing growing-season and mean annual δDp estimates from an elevation-explicit, detrended interpolation model and growing-season δDp estimates from simple Kriging, all indicate that strong isotope gradients occur across Europe with a general depletion occurring in a northeast direction. The feather data, representing 141 individuals of 25 avian species from 38 sites, ranged from �131 to �38‰. Regression analysis showed that strong correlations existed between both mean annual and growing-season δDp estimated by detrended interpolation and δDf of non-aquatic and non- corvid birds (r 2 =0.66 and 0.65, respectively). We also examined mean annual and growing-season δ 18 Op vs. δ 18 Of for our samples. Both oxygen regressions were similar (r 2 =0.56 and 0.57, respectively) but poorer than for deuterium. Our study reveals that δD measurements of feathers from migratory birds in Europe may be used to track their origin and movements, and so provide a powerful investigative tool for avian migration research in Europe.
199 citations
TL;DR: An exponential model described patterns of isotopic turnover for 13C and 15N, and turnover rates and half-lives of the two isotopes were correlated, confirming the assumption of synchronous patterns of turnover for those isotopes.
Abstract: Avian studies are often interpreted using dual (e.g. 13C, 15N) isotope models, assuming turnover of both isotopes occur at similar rates, but only a few studies have quantified turnover rates for more than one of those isotopes simultaneously. To test the generality of previous turnover and fractionation estimates and assumption of synchronous C and N patterns of turnover rates, we captured Dunlin (Calidris alpina pacifica) wintering in the Fraser River Delta, British Columbia, and derived isotopic turnover rates and diet-tissue fractionation factors by experimentally manipulating diet. Birds (n = 15) were initially fed a terrestrially derived diet (mean δ13C: −24.7‰, mean δ15N: 3.5‰) for 54 days. A treatment group (n = 11) was then switched to a marine-derived diet (mean δ13C: −18.3‰, mean δ15N: 13.7‰); a control group (n = 4) was maintained on the terrestrial diet for a further 59 days. An exponential model described patterns of isotopic turnover for 13C and 15N, and turnover rates and half-liv...
171 citations
TL;DR: Stable-isotope analyses of egg components can illuminate the contributions of endogenous and exogenous nutrients to egg formation in cases where birds move from one isotopic biome to another just before egg-laying, as in Red Knots and Ruddy Turnstones nesting in the northeastern Canadian High Arctic.
Abstract: Stable-isotope analyses of egg components can illuminate the contributions of endogenous and exogenous nutrients to egg formation in cases where birds move from one isotopic biome to another just before egg-laying, as in Red Knots (Calidris canutus islandica) and Ruddy Turnstones (Arenaria interpres interpres) nesting in the northeastern Canadian High Arctic. Those populations use inshore marine habitats during the winter and northward migration periods, but switch to feeding and breeding in terrestrial C-3 habitats in the Arctic. Upon the birds' arrival at Alert, Nunavut, Canada, stable carbon (δ13C) and nitrogen (δ15N) isotope values for their red blood cells were consistent with those expected from an inshore marine diet. After the birds switched to a terrestrial diet, those values decayed in a negative exponential fashion until they reached asymptotic values consistent with a local terrestrial C-3 diet. Components of eggs laid later in the season, including lipid-free yolk, albumen, yolk lipi...
142 citations
TL;DR: Based on stable isotope values of individuals, groups of phylogenetically related species generally showed a high degree of overlap within each group, and coexistence could be interpreted as a consequence of superabundance of food or species diversification in morphology and foraging strategies.
Abstract: Summary 1. Food web interactions in animal communities can be investigated through the measurement of stable isotopes (e.g. δ 15 N, δ 13 C). We used this approach in a community of 14 species of seabirds breeding on the Argentinean Patagonian coast. Tissue samples were collected from nestling and adult seabirds, as well as prey, during three consecutive breeding seasons in 28 breeding colonies. 2. Relative to those in other temperate and polar regions, this seabird community showed a high degree of overlap in trophic level (TL) among species (93% of species within a TL range of 0·7) and also a comparatively high mean trophic level (4·1). 3. Relative positions of seabirds in relation to prey suggest that most species feed on pelagic fish and to a lesser extent on invertebrates. Stable isotope values of specialist feeders, Olrolg’s ( Larus atlanticus ) and dolphin gulls ( Leucophaeus scoresbii ), which were previously assumed to feed mainly on crabs and sea lion excrement, respectively, suggested a broader diet than expected. 4. Based on stable isotope values of individuals, groups of phylogenetically related species generally showed a high degree of overlap within each group. 5. Given the degree of isotope overlap in this species-rich community, coexistence could be interpreted as a consequence of superabundance of food or species diversification in morphology and foraging strategies. The short range of trophic level makes these seabirds vulnerable to the reduction of fish stocks due either to commercial fishing or stochastic fluctuations.
130 citations
TL;DR: Positive relationships between delta15N (estimator of trophic level) and OC concentrations (lipid basis) were found for all OC groups, showing that troPHic position and biomagnification significantly influence OC concentrations in Arctic seabirds.
104 citations
TL;DR: Using stable-hydrogen and carbon isotope analyses of the feathers of 139 American Redstarts and 193 Ovenbirds to evaluate evidence for individuals molting feathers at locations other than their breeding sites from the previous year, evidence for long-distance dispersal ranging from 0–29% of individuals is found.
Abstract: Understanding movements of individual birds between breeding sites (breeding dispersal) or between natal sites and the site of first breeding (natal dispersal) is crucial to the modeling of population dynamics. Unfortunately, these aspects of demography are poorly understood for avian species in general, and for migratory songbirds in particular. This is because it is often impossible to sample broadly enough to relocate marked birds that have moved. We used stable-hydrogen (δD) and carbon (δ13C) isotope analyses of the feathers of 139 American Redstarts (Setophaga ruticilla) and 193 Ovenbirds (Seiurus aurocapillus) to evaluate evidence for individuals molting feathers at locations other than their breeding sites from the previous year. We sampled outer rectrices from breeding populations at three extensive boreal forest sites (Prince Albert National Park and Duck Mountain, Saskatchewan, and Lac La Biche, Alberta) and at three isolated forest tracts (Cypress Hills, and Moose Mountain, Saskatchewa...
88 citations
TL;DR: This paper investigated the relationship between warbler abundance and survival rates measured on a Puerto Rican wintering site and rainfall patterns measured on the wintering sites and in regions where these warbler breed, as estimated using stable-isotope analysis (δD) of feathers collected from wintering birds.
Abstract: We investigated relationships between warbler abundance and survival rates measured on a Puerto Rican wintering site and rainfall patterns measured on the wintering site and in regions where these warblers breed, as estimated using stable-isotope analysis (δD) of feathers collected from wintering birds. We banded birds using constant-effort mist netting from January 1989–2003 in the Gu´nica Forest of southwestern Puerto Rico. Black-and-white Warblers (Mniotilta varia), American Redstarts (Setophaga ruticilla), and Ovenbirds (Seiurus aurocapilla) dominated the Neotropical migrant capture totals each winter, with resulting sample sizes large enough to estimate survival rates. Estimates of capture probability from survival modeling allowed us to estimate abundance from mist-netting capture totals for Black-and-white Warblers and Ovenbirds. Stable-hydrogen isotopes showed that the three focal species came mostly from the eastern United States. Black-and-white Warbler abundance was related to rainfall...
65 citations
TL;DR: It is suggested that fluctuating selection or migration–selection balance may maintain the observed polymorphism in stable–isotope profiles of feathers grown in the African winter quarters from a Danish breeding population of adult barn swallows, Hirundo rustica.
Abstract: Population studies assume that individuals belonging to a study population are homogeneous for natal and breeding origin, although this assumption is rarely tested. We tested for heterogeneity in s...
57 citations
TL;DR: In this paper, the authors used banding data from King Eiders (Somateria spectabilis) at Karrak Lake, Nunavut, Canada, during 2001 and 2002 in conjunction with analysis of naturally occurring stable isotopes (13C, 15N) from feathers to connect winter and breeding areas of individuals.
Abstract: We used banding data from King Eiders (Somateria spectabilis) at Karrak Lake, Nunavut, Canada, during 2001 and 2002 in conjunction with analysis of naturally occurring stable isotopes (13C, 15N) from feathers to connect winter and breeding areas of individuals. We also investigated the occurrence of winter philopatry among nesting females, and examined cross-seasonal effects of wintering area on subsequent breeding. Isotopic data suggested that 66–73% of this central-arctic breeding population wintered to the west (i.e., Bering Sea and North Pacific) and the remaining 24–37% wintered to the east (i.e., west Greenland, northwest Atlantic). In contrast, limited band recoveries from hunter-killed King Eiders marked at the same breeding location suggested that about 56% of individuals were shot in eastern wintering areas. These differences likely reflect stronger hunting pressures along the coast of Greenland, which result in more band recoveries for this area. Our results suggest that female King Ei...
54 citations
TL;DR: The general pattern of increasing 615N values among Steller sea lions supports previous conclusions regarding a reduction or redistribution of forage fishes and an increase of demersal and semi-demersal species in the North Pacific ecosystem.
Abstract: Stable isotope (615N and 6°C) values of individual tooth annuli of female Steller sea lions (n = 120) collected from the 1960s through the 1980s were used for retrospective analyses of temporal changes in food webs in the Gulf of Alaska and North Pacific Ocean. We also examined isotopically contour feathers of tufted puffins (n = 135) and crested auklets (n = 37) through this period to test for broader isotopic patterns indicative of whole food web changes. Steller sea lions decreased slightly in 6I3C and increased in 6”N values, suggesting an increasing trophic level and change in foraging location or oceanographic isotopic signature. Steller sea lion first and second tooth annuli were enriched in 15N and depleted in 13C compared with subsequent annuli, indicating the effects of maternal influence through weaning. The general pattern of increasing 615N values among Steller sea lions supports previous conclusions regarding a reduction or redistribution of forage fishes and an increase of demersal and semi-demersal species in the North Pacific ecosystem. There were no significant changes in 6I5N values for either bird species. However, 6I3C values in both bird species again suggested changes in foraging location or a shift in oceanographic currents.
TL;DR: In this paper, the natal grounds of Cuban monarchs were determined through the combined use of stable hydrogen (δD) and stable carbon isotope measurements and by cardenolide fingerprint analysis using thin-layer chromatography (TLC).
Abstract: Since the discovery of monarch butterfly (Danaus plexippus) overwintering colonies in Mexico in the 1970s, it was assumed that monarchs from eastern North America migrated only to Mexico. This paper reveals that monarchs from Canada and the east coast of the United States also regularly travel to Cuba during the migration period. The natal grounds of Cuban monarchs were determined through the combined use of stable hydrogen (δD) and stable carbon (δ13C) isotope measurements and by cardenolide fingerprint analysis using thin-layer chromatography (TLC). The TLC data revealed that there was an influx of migrants in November to Cuba, and the stable isotope data revealed that migrant Cuban monarchs originated from southeastern Canada and the eastern United States. Our findings suggest that North American migrant monarchs that move to Cuba hybridize with resident populations there and do not return to the continent. The differences in the natal grounds, migratory route, and reproductive stages between monarchs ...
TL;DR: Whole baleen C and N isotopes were better correlated with tissue Hg levels, suggesting that balean may provide a more reliable indicator of long-term average diet, which in turn may be better related to Hg accumulation in tissues than the shorter-term diet record contained in muscle.
TL;DR: Redhead females relied mainly on dietary lipids and proteins for egg production, and therefore endogenous reserves were used to satisfy female body maintenance and energy requirements.
Abstract: Summary
1Clutch formation represents a considerable energy expense for waterfowl, yet little evidence is available to quantify nutrient allocation from endogenous and exogenous sources. Here we investigated hydrogen and carbon stable isotope ratios (δD and δ13C) in female Redhead Ducks (Aythya americana) and their eggs to evaluate the use of δD as an indicator of nutrient sources to reproduction.
2Females arrived with mean muscle tissue δD and δ13C values more positive than those of the local food web, reflecting marine dietary inputs from the wintering grounds. These values changed to the range of local food values by late incubation. δ13C values from albumen and yolk protein were correlated, supporting the presence of a common exogenous carbon source for these egg components.
3There was no significant correlation between δD or δ13C values in egg tissues and abdominal fat or muscle from the corresponding laying female. No general population-level trends in isotope values from sequentially developing follicle yolks were found.
4Redhead females relied mainly on dietary lipids and proteins for egg production, and therefore endogenous reserves were used to satisfy female body maintenance and energy requirements.
TL;DR: SigmaPCBs, DDTs, HCHs and toxaphenes seem to be at similar levels in West Greenland and Arctic Canada, which can be explained by the close winter distributions of populations as well as large ranges in concentrations, time span, number of analyses and the size/age composition of the data.
TL;DR: Factors affecting dynamics of highly mobile bird populations are particularly difficult to decipher because of varying environmental conditions and habitat changes among breeding, migration, and wintering areas.
Abstract: The astonishing diversity of avian movement patterns, reproductive tactics, and survival rates creates rich opportunities for study, but also presents enormous challenges for explaining variation among life-history traits and dispersal. Dispersal decisions shape the genetic structure of populations and thus can be of considerable importance in processes such as speciation. Moreover, a better understanding of dispersal and movement among populations remains fundamental for effective conservation strategies for a great many species. Factors affecting dynamics of highly mobile bird populations are particularly difficult to decipher because of varying environmental conditions and habitat changes among breeding, migration, and wintering areas. Depending on species, dispersal by individual birds involves movements of 1000 km
TL;DR: This study evaluated if male age and body size, density of conspecifics, and arthropod biomass contributed to variation in territory size and overlap of Ovenbirds, Seiurus aurocapillus, in a fra...
Abstract: We evaluated if male age and body size, density of conspecifics, and arthropod biomass contributed to variation in territory size and overlap of Ovenbirds, Seiurus aurocapillus (L., 1766), in a fra...
TL;DR: In this paper, the abundance of naturally occurring deuterium (δD) in feathers grown in North America can provide geographical information on location where the feather was grown, and they used this technique to link populations of Bicknell's thrush (Catharus bicknelli) breeding in northeastern North America (to 46°N) with wintering grounds in the Dominican Republic.
Abstract: The measurement of the abundance of naturally occurring deuterium (δD) in feathers grown in North America can provide geographical information on location where the feather was grown. Previously, we used this technique to link populations of Bicknell's Thrush (Catharus bicknelli) breeding in northeastern North America (to 46°N) with wintering grounds in the Dominican Republic. That study indicated the presence of a subpopulation of wintering birds with more depleted feather δD values than those measured on their known breeding grounds. This suggested either a more northerly or a higher altitude breeding source population than previously measured. We located two populations of Bicknell's Thrush in Quebec, Canada, at Mine Madeleine (49°N) and at Mont Gosford (45°N). The Mine Madeleine birds had feather δD values overlapping those of the unidentified subpopulation found wintering in the Dominican Republic. At Mont Gosford, hatch-year birds were more depleted in their feather δD values than after-sec...
TL;DR: In this article, the authors look at trace element concentrations and isotopic ratios of carbon and nitrogen as contained in baleen from bowhead whales in the eastern and western Arctic Ocean and apply time series techniques, including maximum likelihood method and likelihood ratio tests, to analysis of data and inference about their mean structures.
Abstract: A temporal record of environmental conditions is often contained within accretionary biological tissue. These records can provide knowledge of the environmental conditions that existed at the time the tissue was formed. In this study, we look at trace element concentrations and isotopic ratios of carbon and nitrogen as contained in baleen from bowhead whales in the eastern and western Arctic Ocean. Time series techniques, including maximum likelihood method and likelihood ratio tests, are applied to analysis of data and inference about their mean structures.
01 Jan 2004
TL;DR: In this article, the authors present an overview of stable isotopic applications to time-integrated trophic reconstructions, source of feeding, behaviour of contaminants in the field of isotopic tracing in polar food webs with specific reference to Jan Mayen.
Abstract: Polar environments pose logistical challenges for fieldwork designed to elucidate dietary history of individual organisms, trophic relationships among individuals and species, and the ultimate role of species in the flux of energy, elements, and contaminants. Stable isotopic tools delineate dietary histories of organisms that extend well beyond the periods when individuals are physically available. By examining tissues with both long- and short-turnover rates, a long-term dietary picture emerges. Tissues such as blood plasma and cellular fractions, feathers, nail, hair, and even breath carbon dioxide may often provide opportunity for non-destructive sampling protocols. This paper presents an overview of stable isotopic applications to time-integrated trophic reconstructions, source of feeding, behaviour of contaminants in the field of isotopic tracing in polar food webs with specific reference to Jan Mayen.