Abstract
The non‐breeding period is critical for restoration of body condition and self‐maintenance in albatrosses, yet detailed information on diet and distribution during this stage of the annual cycle is lacking for many species. Here, we use stable isotope values of body feathers (δ13C, δ15N) to infer habitat use and trophic level of non‐breeding adult Grey‐headed Albatrosses Thalassarche chrysostoma (n = 194) from South Georgia. Specifically, we: (1) investigate intrinsic drivers (sex, age, previous breeding outcome) of variation in habitat use and trophic level; (2) quantify variation among feathers of the same birds; and (3) examine potential carry‐over effects of habitat use and trophic level during the non‐breeding period on subsequent breeding outcome. In agreement with previous tracking studies, δ13C values of individual feathers indicate that non‐breeding Grey‐headed Albatrosses from South Georgia foraged across a range of oceanic habitats, but mostly in subantarctic waters, between the Antarctic Polar Front and Subtropical Front. Sex differences were subtle but statistically significant, and overlap in the core isotopic niche areas was high (62%); however, males exhibited slightly lower δ13C and higher δ15N values than females, indicating that males forage at higher latitudes and at a higher trophic level. Neither age nor previous breeding outcome influenced stable isotope values, and we found no evidence of carry‐over effects of non‐breeding habitat use or trophic level on subsequent breeding outcome. Repeatability among feathers of the same individual was moderate in δ13C and low in δ15N. This cross‐sectional study demonstrates high variability in the foraging and migration strategies of this albatross population.
Highlights
Individual seabirds within apparently generalist populations may differ in their resource use and foraging strategies (Phillips et al 2017), with potential implications for community structure, evolutionary ecology and conservation
Using the stable isotope method, we test the following a priori predictions: (1) most feather d13C values should correspond to foraging in the Sub-Antarctic Zone (SAZ); (2) there will be sex differences in stable isotope values, consistent with the degree of sexual size dimorphism (SSD); (3) d13C values will decrease with age, as demonstrated in similar studies of Wandering Albatrosses (Jaeger et al 2014, Clay et al 2018); (4) stable isotope values of feathers sampled from the same individual should show high variability given the protracted moult pattern in this species; and (5) there will be carry-over effects of variation in diet and distribution
Rather less is known about the foraging ecology of albatrosses during the non-breeding compared with the breeding season
Summary
Individual seabirds within apparently generalist populations may differ in their resource use and foraging strategies (Phillips et al 2017), with potential implications for community structure, evolutionary ecology and conservation. This includes the relative reliance on an inshore vs offshore, benthic vs pelagic diet, and latitude or water mass where a gradient exists, such as in the Southern Ocean (Quillfeldt et al 2005, 2010, Cherel & Hobson 2007, Jaeger et al 2010) The aim of this cross-sectional study is to provide detailed information on the foraging ecology of Grey-headed Albatrosses Thalassarche chrysostoma from South Georgia during the non-breeding period. Previous breeding outcome may influence the stable isotope values, or the latter may influence the subsequent breeding outcome; without further information we make no a priori predictions about the directions of these relationships
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