Journal Article

Long-term individual foraging site fidelity-why some gannets don't change their spots

Bodey, Thomas W., Votier, Stephen C., Bearhop, Stuart, Davies, Rachel D., Newton, Jason, Cleasby, Ian R., Wakefield, Ewan D., Miller, Peter I., Hamer, Keith C.

2015

Overview

Many established models of animal foraging assume that individuals are ecologically equivalent. However, it is increasingly recognized that populations may comprise individuals who differ consistently in their diets and foraging behaviors. For example, recent studies have shown that individual foraging site fidelity (IFSF, when individuals consistently forage in only a small part of their population's home range) occurs in some colonial breeders. Short-term IFSF could result from animals using a win-stay, lose-shift foraging strategy. Alternatively, it may be a consequence of individual specialization. Pelagic seabirds are colonial central-place foragers, classically assumed to use flexible foraging strategies to target widely dispersed, spatiotemporally patchy prey. However, tracking has shown that IFSF occurs in many seabirds, although it is not known whether this persists across years. To test for long-term IFSF and to examine alternative hypotheses concerning its cause, we repeatedly tracked 55 Northern Gannets ( Morus bassanus ) from a large colony in the North Sea within and across three successive breeding seasons. Gannets foraged in neritic waters, predictably structured by tidal mixing and thermal stratification, but subject to stochastic, wind-induced overturning. Both within and across years, coarse to mesoscale (tens of kilometers) IFSF was significant but not absolute, and foraging birds departed the colony in individually consistent directions. Carbon stable isotope ratios in gannet blood tissues were repeatable within years and nitrogen ratios were also repeatable across years, suggesting long-term individual dietary specialization. Individuals were also consistent across years in habitat use with respect to relative sea surface temperature and in some dive metrics, yet none of these factors accounted for IFSF. Moreover, at the scale of weeks, IFSF did not decay over time and the magnitude of IFSF across years was similar to that within years, suggesting that IFSF is not primarily the result of win-stay, lose-shift foraging. Rather, we hypothesize that site familiarity, accrued early in life, causes IFSF by canalizing subsequent foraging decisions. Evidence from this and other studies suggests that IFSF may be common in colonial central-place foragers, with far-reaching consequences for our attempts to understand and conserve these animals in a rapidly changing environment.

• Publisher: Ecological Society of America
• Subject: Animal Distribution / Animal models / Animal populations / Animal reproduction / Animals / Aquatic birds / Aviculture / Bass Rock, North Sea / Birds / Birds - physiology / Blood / Body Composition / breeding season / Breeding seasons / central-place forager / Changing environments / Decay / Diet / Ecosystem / Environmental changes / Familiarity / Feeding Behavior - physiology / Forage / Foraging / Foraging behavior / foraging site fidelity / Gannets / GPS tracking / Habitat selection / Habitat utilization / Home range / individual specialization / Isotope ratios / Isotopes / Marine ecology / mixing / Morus bassanus / niche / nitrogen / North Sea / Northern Gannet / partitioning / philopatry / Sea birds / Sea surface temperature / seabirds / site familiarity / Site fidelity / Stable isotopes / surface water temperature / temperature profiles / Thermal stratification / tidal mixing front / Time Factors / tissues