Abstract

Sexual segregation (SS) is widespread among animal taxa, with males and females segregated in distribution, behavior, or feeding ecology but so far, most studies on birds have focused on the breeding period. Outside this period, the relevance of segregation and the potential drivers of its persistence remain elusive, especially in the marine environment, where animals can disperse over vast areas and are not easily observed. We evaluated the degree of SS in spatio‐temporal distribution and phenology, at‐sea behavior, and feeding ecology during the nonbreeding period among three closely related shearwaters: Scopoli's, Cory's, and Cape Verde shearwaters (Calonectris diomedea, C. borealis, and C. edwardsii, respectively). We tracked 179 birds (92 males and 87 females) from 2008 to 2013 using geolocation‐immersion loggers and collected the 13th secondary remige (molted in winter) for stable isotope analyses as a proxy of trophic level and diet. The global nonbreeding distribution did not differ between sexes for the three species, but one specific nonbreeding area was visited only by males. Cory's shearwater males remained in areas closer to the colony in a larger proportion compared to females and returned earlier to the colony, probably to defend their nests. Males presented a slightly lower nocturnal flying activity and slightly (but consistently) higher isotopic values of δ13C and δ15N compared to females. These differences suggest subtle sexual differences in diet and a slightly higher trophic level in males, but the extent to which sexual dimorphism in bill size can determine them remains unclear. Our study showed that SS in ecological niche in seabirds can persist year‐round consistently but at a different extent when comparing the breeding and nonbreeding periods. Based on our findings, we propose that SS in these seabird species might have its origin in an ecological specialization derived from the different roles of males and females during reproduction, rather than from social dominance during the nonbreeding period.

Highlights

  • Sexual segregation (SS) is a widespread behavioral and ecological phenomenon in animal taxa (Rubin & Bleich, 2005)

  • Cory's shearwater males preferred to remain closer to the breeding grounds during the nonbreeding period compared to females

  • Sex‐related differences in several parameters of the migration phenology were found, with males leaving and ar‐ riving earlier than females at the breeding grounds. This could be attributed to differential reproductive roles, in particular to the greater involvement of males in nest defense, rather than to male social dominance

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Summary

Introduction

Sexual segregation (SS) is a widespread behavioral and ecological phenomenon in animal taxa (Rubin & Bleich, 2005). The eco‐ logical specialization hypothesis proposes that habitat segregation arises from sex‐specific preferences, tolerance to ecological fac‐ tors, or specialization in reproductive roles (Carey, 1996; Ketterson & Nolan, 1983; Morton, 1990; Selander, 1966). Both hypotheses are not mutually exclusive, and their underlying mechanisms can co‐occur and be both cause and consequence (Catry et al, 2005; González‐Solís, Croxall, & Wood, 2000; Shine, 1989)

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