Combined bio-logging and stable isotopes reveal individual specialisations in a benthic coastal seabird, the Kerguelen shag
Résumé
Individual specialisations, which involve the repetition of specific behaviours or dietary
choices over time, have been suggested to benefit animals by avoiding competition with
conspecifics and increasing individual foraging efficiency. Among seabirds, resident and
benthic species are thought to be good models to study inter-individual variation as they
repetitively exploit the same environment. We investigated foraging behaviour, isotopic
niche and diet in the Kerguelen shag Phalacrocorax verrucosus during both the incubation
and chick-rearing periods for the same individuals to determine the effect of sex, breeding
stage, body mass and morphometrics on mean foraging metrics and their consistency.
There were large differences between individuals in foraging behaviour and consistency,
with strong individual specialisations in dive depths and heading from the colony. Stable isotopes
revealed specialisations in feeding strategies, across multiple temporal scales. Specifically,
individuals showed medium term specialisations in feeding strategies during the
breeding season, as well as long-term consistency. A clustering analysis revealed 4 different
foraging strategies displaying significantly different δ15N values and body masses.
There were no sex or stage biases to clusters and individuals in different clusters did not differ
in their morphology. Importantly, the results suggest that the different strategies emphasized
were related to individual prey preferences rather than intrinsic characteristics.