Causes and consequences of individual variability and specialization in foraging and migration strategies of seabirds

Abstract

Technological advances in recent years have seen an explosion of tracking and stable isotope studies of seabirds, often involving repeated measures from the same individuals. This wealth of new information has allowed the examination of the extensive variation among and within individuals in foraging and migration strategies (movements, habitat use, feeding behaviour, trophic status, etc.) in unprecedented detail. Variation is underpinned by key life-history or state variables such as sex, age, breeding stage and residual differences among individuals (termed 'individual specialization'). This variation has major implications for our understanding of seabird ecology, because it affects the use of resources, level of intra-specific competition and niche partitioning. In addition, it determines the responses of individuals and populations to the environment and the susceptibility to major anthropogenic threats. Here we review the effects of season (breeding vs. nonbreeding periods), breeding stage, breeding status, age, sex and individual specialization on foraging and migration strategies, as well as the consequences for population dynamics and conservation.

Does sexual segregation occur during the nonbreeding period? A comparative analysis in spatial and feeding ecology of three Calonectris shearwaters

“…In the three species, δ 13 C and δ 15 N values of the S13 remige (molted during the nonbreeding season) were slightly higher in males than in females. In seabirds, sexual differences in isotope ratios are often documented during different stages of the breeding period, but do not necessarily remain consistent year‐round (Phillips, Lewis, González‐Solís, & Daunt, ; Phillips et al, ). The slight differences between sexes in δ 13 C and δ 15 N values found in our study suggest a small dietary segregation between sexes of the three species during the nonbreeding period.…”

Moult location and diet of auks in the North Sea inferred from coupled light-based and isotopebased geolocation

“…Isotopic residual variability differed between feather types and between species, suggesting different population-and individualscale foraging strategies, during different feather moult time periods. Whilst observed differences in residual isotopic variability seem biologically plausible in terms of dietary differences, variability could also be a result of spatially diverse foraging locations, different body conditions or potentially different mela nin content across the different feather types (Michalik et al 2010, McMahon et al 2015, Phillips et al 2017). Further work is needed to clarify these sources of variation.…”

Short‐term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator

“…; birds: Phillips et al . ). Studying the mechanisms by which individual specialisation arises is critical to test theoretical approaches (Bolnick et al .…”

“…Individual specialisation in resource selection offers a selective advantage if individuals increase foraging efficiency by reducing search times, and this is related to their abilities to locate prey (Spiegel & Crofoot ) and to prey predictability (Phillips et al . ). When prey distributions are predictable, predators can reduce search time using memory (Weimerskirch ; Wakefield et al .…”