Stable isotopes reveal individual variation in migration strategies and habitat preferences in a suite of seabirds during the nonbreeding period

Abstract

Information on predator and prey distributions is integral to our understanding of migratory connectivity, food web dynamics and ecosystem structure. In marine systems, although large animals that return to land can be fitted with tracking devices, minimum instrument sizes preclude deployments on small seabirds that may nevertheless be highly abundant and hence major consumers. An increasingly popular approach is to use N and C stable isotope analysis of feathers sampled at colonies to provide information on distribution and trophic level for the preceding, and generally little-known, nonbreeding period. Despite the burgeoning of this research, there have been few attempts to verify such relationships. In this study, we demonstrate a clear correspondence between isotope ratios of feathers and nonbreeding distributions of seven species from South Georgia tracked using loggers. This generated a rudimentary isoscape that was used to infer the habitat preferences of eight other species ranging in size from storm petrels to albatrosses, and which could be applied, with caveats, in other studies. Differences in inferred distribution within and between species had major implications for relative exposure to anthropogenic threats, including climate change and fisheries. Although there were no differences in isotope values between sexes in any of the smaller petrels, mean stable C (delta(13)C), but not stable N isotope ratios (delta(15)N), tended to be greater in females than males of the larger, and more sexually size-dimorphic species. This indicates a difference in C source (distribution), rather than trophic level, and a correspondence between the degree of sexual size dimorphism in Procellariiformes and the level of between-sex niche segregation.

Spatial and isotopic niche partitioning during winter in chinstrap and Adélie penguins from the South Shetland Islands

“…The observed differences within and between species indicates that isotope signatures from penguin tail feathers may be a useful tracer for identifying large-scale movement patterns of Adélie and chinstrap penguins, similar to other Southern Ocean seabirds (e.g., Cherel and Hobson 2007, Phillips et al 2009, Jaeger et al 2010. However, it is important to note that consumer stable isotope values can change over time due to shifts in dietary composition or movement between geographic location with differing isotopic baselines (e.g., Cherel and Hobson 2007, Brasso and Polito 2013, McMahon et al 2013).…”

Exploiting the closest productive area: geographical segregation of foraging grounds in a critically endangered seabird

“…Unravelling spatial distribution differences within and among species not only helps to understand the ecological links between the components of marine ecosystems; this also helps to identify conservation gaps relative to human threats (Boersma 2008, Phillips et al 2009). For example, Young et al (2009) showed how Laysan albatrosses Phoebastria immutabilis breeding in 2 distant breeding populations in the North Pacific showed differences in patterns of plastic ingestion relative to geographical segregation of foraging grounds.…”

“…Moreover, the isotopic variability found in marine species can be explained by specific oceanographic conditions due to habitat preferences (c.f. Phillips et al 2009) since productive areas related with terrestrial inputs (e.g. river run-offs) might present different isotopic signatures compared to marine-driven productivity areas (e.g.…”

Differences in the timing and extent of annual moult of black-browed albatrosses Thalassarche melanophris living in contrasting environments

“…The only study reporting the regular moult of flight feathers during breeding involved yellownosed albatrosses Thalassarche chlororhynchos and found less than 10 % of the individuals still growing the last of the moulted primaries ([90 % growth completed) at the start of the incubation (Furness 1988). The chemical analysis of albatross feathers is therefore used regularly to obtain information believed to pertain to the nonbreeding period (Cherel et al 2000(Cherel et al , 2013Phillips et al 2009Phillips et al , 2011. During a long-term demographic and ecological study of black-browed albatrosses Thalassarche melanophris in the Falkland Islands (Catry et al 2010Granadeiro et al 2011), we noted the occurrence of moult of feathers of different types in the breeding colony.…”