Movement ecology during non-breeding season in a long-distance migratory shorebird: are space use and movement patterns sex-biased?

Abstract

In many gregarious species, sex-specific differences can lead to significant variation in movement patterns and, consequently, to social and spatial segregation by sex within the population. Specifically, in several long-distance migratory shorebird species, reverse sexual dimorphism has been proposed as a driver of spatial segregation during the non-breeding season. Thus, sex-specific costs associated with space use during these stationary periods could differentially condition subsequent movement patterns between females and males in these species. Using satellite tracking technology, we analyzed the space use and movement patterns of a population of Hudsonian godwits (Limosa haemastica), a gregarious long-distance migratory shorebird, during the non-breeding season in Chiloé, Chile. We predicted that larger females would show more restricted movements and higher local site fidelity, while smaller males would be less competitive and more exploratory. Most individuals exhibited restricted space use (i.e., a home range), while a smaller fraction showed exploratory movements leading to a nomadic movement pattern. Most of these nomadic individuals subsequently oversummered in Argentina rather than migrating back to breeding areas. Contrary to our main prediction, none of the observed movement patterns were sex-biased. Recent evidence suggests that female and male godwits access prey of different sizes within the same foraging sites on Chiloé. Thus, in accordance with our results, and supported by recent additional findings, resource-partitioning within the same foraging patches could reduce interference competition between the sexes by offsetting the competitive advantage associated with the reversed sexual dimorphism of females over males. Finally, we propose these sex differences in foraging strategies could be advantageous for gregarious migratory shorebird populations that show strong connectivity and high site fidelity during and between non-breeding seasons.