The Tristan albatross Diomedea dabbanena is Critically Endangered: >99% of adults breed at Gough Island, central South Atlantic Ocean, where chicks are threatened by introduced predators. At sea they ...mostly remain within the South Atlantic Ocean, where they are threatened by incidental capture in longline fisheries. Conservation measures to reduce seabird mortality in pelagic longline fisheries are confined largely to fishing effort south of 25 degree S. This covers the core range of breeding Tristan albatrosses, but the distribution of non-breeding adults and immature birds is unknown. We tracked 14 non-breeding adult Tristan albatrosses from Gough Island for up to 3 yr, from 2004 to 2006, using geolocating loggers. All birds remained in the South Atlantic or southern Indian Oceans, and showed distributions centred on the Sub-Tropical Convergence. They used the SW Atlantic during the austral summer and the SE Atlantic and Indian Oceans as far east as Australia during the austral winter. Foraging effort was concentrated in areas of upwelling and increased productivity. The distribution of the tracked birds overlapped with a range of pelagic longline fisheries, especially off southern Africa. Of particular concern was that 2 birds spent several months off the coast of Namibia and in adjacent high seas north of 25 degree S, where there are currently no regulations to prevent seabird bycatch during pelagic longline fishing operations.
Although predicted some time ago, there has been little success in demonstrating that the overall fitness of migratory birds depends on the combined influences of their experiences over all seasons. ...We used stable carbon isotope signatures (δ13C) in the claws of migrating black-throated blue warblers Dendroica caerulescens to infer their wintering habitats and investigated whether winter habitat selection can be linked to condition during migration. Resident bird species with low δ13C corresponded to selection of more mesic habitats, and migrating birds with low δ13C were in better condition than conspecifics with higher δ13C signatures. These findings concur with empirical observations on the wintering grounds, where dominants (mostly males) tend to exclude subordinates from mesic areas (considered to be high-quality habitats). We believe that variation in condition during migration may be one of the key factors determining differences in arrival times and condition at the breeding areas, which in turn have a major influence on reproductive success.
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The rockhopper penguin (Eudyptes chrysocome) is a conspicuous apex marine predator that has experienced marked population declines throughout most of its circumpolar breeding distribution. The ...cause(s) for the declines remain elusive, but the relatively large spatio-temporal scale over which population decreases have occurred implies that ecosystem-scale, at-sea factors are likely to be involved. We employ stable isotope analyses of carbon (¹³C/¹²C, expressed as delta¹³C) and nitrogen (¹⁵N/¹⁴N, delta¹⁵N) in time-series of rockhopper penguin feather samples, dating back to 1861, in order to reconstruct the species' ecological history. Specifically, we examine whether rockhopper penguin population decline has been associated with a shift towards lower primary productivity in the ecosystem in which they feed, or with a shift to a diet of lower trophic status and lower quality, and we use long-term temperature records to evaluate whether shifts in isotope ratios are associated with annual variations in sea surface temperature. Having controlled temporally for the Suess Effect and for increases in CO₂ concentrations in seawater, we found that overall, delta¹³C signatures decreased significantly over time in rockhopper penguins from seven breeding sites, supporting the hypothesis that decreases in primary productivity, and hence, carrying capacity, for which delta¹³C signature is a proxy, have been associated with the decline of penguin populations. There was some evidence of a long-term decline in delta¹⁵N at some sites, and strong evidence that delta¹⁵N signatures were negatively related to sea surface temperatures across sites, indicative of a shift in diet to prey of lower trophic status over time and in warm years. However, a site-by-site analysis revealed divergent isotopic trends among sites: five of seven sites exhibited significant temporal or temperature-related trends in isotope signatures. This study highlights the utility of stable isotope analyses when applied over relatively long timescales to apex predators.
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1. The potential of using stable isotope signatures of avian claws in order to infer diet and habitat use was investigated. 2. Highly significant relationships observed between stable carbon and ...nitrogen isotope ratios$(\delta {}^{13}\text{C},\delta {}^{15}\text{N})$in the claws and body feathers of resident birds were expected since it was predicted that they were synthesized in the same habitat and approximately the same time of year. 3. Likewise the non-significant relationships observed between δ13C and δ15N in the claws and tertial feathers of neotropical migrant birds were also predicted since the claws were synthesized in the wintering area and the tertials in the breeding area. 4. The growth rates measured in the claws of five species of palearctic passerines provide evidence that this tissue should integrate dietary and habitat information over a medium temporal scale (probably weeks to months). 5. It is suggested that claws may offer a unique combination of attributes to the isotope ecologist: they are non-invasively sampled; metabolically inert but grow continuously, and are therefore a more flexible tool than feathers. 6. It is also suggested that that the stable isotope signatures in the claws of mammals and reptiles may provide similar information.
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Incubation is an energetically demanding process for parents, in part because of the thermodynamic costs of maintaining egg temperature. One might predict that aspects of nest construction—in ...particular, the thermodynamic properties of the nesting material and the degree to which the nest provides shelter from the wind—would have important effects on thermodynamic costs. However, little is known about the relative importance of those factors. Here, we investigate egg cooling rates in several commonly used nesting materials and in various wind speeds and examine the effect on those rates of wetting the materials. Nesting materials differ greatly in their insulating properties; feather down is the best insulator, and grass the worst. When the materials are wet, eggs cool much more rapidly, differences between materials tend to diminish, and down becomes the worst insulator. Hence, there may be significant selection pressure to choose particular nesting materials, but materials may be better or worse according to the situation of the nest. Increasing wind speed also has profound effects on egg cooling rates, even at the low speeds tested here, which implies strong selection pressure to locate and construct nests that minimize wind speed at the egg surface. Our results suggest that nest construction may have an important bearing on the subsequent costs of reproduction, and that important trade-offs may exist between nest construction for reduced thermodynamic costs, and other costs and benefits of nest-building and reproduction.
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Understanding the links between breeding and wintering areas of migratory species has important ecological and conservation implications. Recently, stable isotope technology has been used to further ...our understanding. Stable isotope ratios vary geographically with a range of biogeochemical factors and isotope profiles in organisms reflect those in their food and environment. For inert tissues like feathers, isotope profiles reflect the environment in which they were formed. Following large-scale habitat destruction, the globally threatened aquatic warbler Acrocephalus paludicola has a fragmented breeding population across central Europe, largely in Belarus, Poland and Ukraine. The species' sub-Saharan African wintering grounds have not yet been discovered, and this significantly hampers conservation efforts. Aquatic warblers grow their flight feathers on their wintering grounds, and we analysed stable isotope ratios ($\delta^{15} {\rm{N,}}\,\delta^{13} {\rm{C,}}$δD) in rectrices of adults from six main breeding sites (subpopulations) across Europe to determine whether different breeding subpopulations formed a single mixed population on the wintering grounds.$\delta^{15} {\rm{N}}$varies considerably with dietary trophic level and environmental factors, and δD with the δD in rainfall; neither varied between aquatic warbler subpopulations. Uniform feather$\delta^{15} {\rm{N}}$signatures suggest no major variation in dietary trophic level during feather formation. High variance and inter-annual differences in mean δD values hinder interpretation of these data. Significant differences in mean$\delta^{13} {\rm{C}}$ratios existed between subpopulations. We discuss possible interpretations of this result, and consider differences in moulting latitude of different subpopulations to be the most parsimonious.$\delta^{13} {\rm{C}}$in plants and animals decreases with latitude, along a steep gradient in sub-Saharan Africa. Birds from the most north-westerly breeding subpopulation (Karsibor, Poland) had significantly lower variance in$\delta^{13} {\rm{C}}$and$\delta^{15} {\rm{N}}$than birds from all other sites, suggesting either that birds from Karsibor are less geographically dispersed during moult, or moult in an area with less isotopic heterogeneity. Mean$\delta^{13} {\rm{C}}$signatures from winter-grown feathers of different subpopulations were positively correlated with the latitude and longitude of breeding sites, suggesting a strong relationship between European breeding and African winter moulting latitudes. The use of stable isotopes provides novel insights into migratory connectivity and migration patterns in this little-known threatened species.
Past studies have indicated that Pacific rats Rattus exulans are significant predators of the chicks of surface-breeding seabirds, namely gadfly petrels Pterodroma spp., on Henderson Island, central ...South Pacific. Further fieldwork in 2003 confirmed the heavy predation of chicks of Murphy's petrel P. ultima by rats. By extension, heavy predation is also likely each year on the endangered Henderson petrel P. atrata, for which Henderson Island is the only confirmed breeding site. To assess how important petrels are in the overall diet of rats, we conducted stable isotope analyses of rats from the shore, where petrels are most concentrated, and from about 1 km inland, where fewer nest. The carbon isotope results suggested that inland rats obtain about 30% of their food from marine sources, while the figure for shore rats was about 40%. We consider factors that may have acted to inflate these proportions. If, as suggested by these results, petrels are not the predominant component of the rats' diet, then rat populations and hence rat predation on petrels may not diminish even if petrel populations decrease further. In the light of probable low annual breeding success, we drew on vital rate information for the cahow P. cahow to model changes in the Henderson petrel population, and found a negative growth rate (lambda = 0.9918) under present conditions. Growth rate became positive if annual adult survival rose above 0.95 or breeding success above 0.25, the latter unlikely while rats remain on Henderson. We conclude that the Henderson petrel population will probably continue to decline in the absence of conservation intervention.
Records of beech masting for Germany, Denmark, The Netherlands, England and Sweden over the past two centuries have been collected from published research. They have been converted to a common ...five‐point scale to permit comparison between masting in different countries and different years. Very good masts occurred in both Germany and Denmark in 1888, 1909 and 1918. Good/very good masts occurred in at least three of the countries in 1909, 1918, 1926, 1948, 1956 and 1976. The number of very poor years which occurred in Europe during the last two centuries is very much greater, with 71 since 1900. Moderate mast years are more likely to occur in only one or two of the countries at a time and have the effect of a partial depletion of resources within the tree, which distorts the masting pattern for following years. There is a presumption for an inherent biennial masting pattern, constrained by the internal resources of the tree, which is then strongly affected by climatic conditions.
The benefits of flocking to prey species, whether through collective vigilance, dilution of risk, or predator confusion, depend on flock members responding in a coordinated way to attack. We ...videotaped sparrowhawks attacking redshank flocks to determine if there were differences in the timing of escape flights between flock members and the factors that might affect any differences. Sparrowhawks are surprise short-chase predators, so variation in the time taken to take flight on attack is likely to be a good index of predation risk. Most birds in a flock flew within 0.25 s of the first bird flying, and all birds were flying within 0.7 s. Redshanks that were vigilant, that were closest to the approaching raptor, and that were close to their neighbors took flight earliest within a flock. Birds in larger flocks took longer, on average, to take flight, measured from the time that the first bird in the flock flew. Most birds took flight immediately after near neighbors took off, but later flying birds were more likely to fly immediately after more distant neighbors took flight. This result, along with the result that increased nearest neighbor distance increased flight delay, suggesting that most redshanks flew in response to conspecifics flying. The results strongly suggest that there is significant individual variation in predation risk within flocks so that individuals within a flock will vary in benefits that they gain from flocking.
Animals often trade off risk of predation and risk of starvation when making foraging decisions. Redshanks, Tringa totanus, wintering in an area of high sparrowhawk, Accipiter nisus, predation were ...studied to determine how simultaneous variations in energy requirements and the risk of predation determine choice of foraging area. In particular, we focus on the effects of weather on this trade-off. Redshanks could either feed on a saltmarsh where both food availability and predation risk are high, or on safer, but less productive, inter-tidal flats. On the saltmarsh, redshanks could choose to feed in profitable but high risk areas close to cover or in lower risk creeks. In general, low temperatures resulted in birds using the saltmarsh habitat more, foraging closer to cover, and making less use of safe creek micro-habitats. This is consistent with low temperatures increasing redshanks' metabolic costs, thus increasing their preparedness to accept higher predation risk for greater foraging returns. At low temperatures sparrowhawks were more successful at catching redshanks, probably as a consequence of adoption of more risky foraging options by the redshanks, but rate of attack was probably not strongly affected by weather. Redshanks responded to precipitation by foraging in areas that reduced their predation risk. When precipitation was high, redshanks also became more prone to false alarm flights. These effects suggest that precipitation may increase predation risk by making the approach of a predator harder to detect. Redshanks foraged further from cover in high winds, suggesting that wind affected predation risk more than starvation risk. Redshanks responded strongly to sparrowhawk activity: use of the saltmarsh was less and redshanks foraged further from cover during days with a high attack frequency.
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