Limited sexual segregation in a dimorphic avian scavenger, the Andean condor

Sexual segregation is widely reported among sexually dimorphic species and generally attributed to intraspecific competition. Prey diversity and human activities can reinforce niche segregation by increasing resource heterogeneity. Here, we explored trophic and spatial sexual segregation in the only avian scavenger that exhibits pronounced sexual size dimorphism (up to 50% difference in body mass) and a highly despotic social system, the Andean condor (Vultur gryphus). We predicted that larger and dominant males would exclude smaller and subordinate females from high-quality resources, leading to sexual segregation particularly in human-dominated landscapes showing increased prey diversity. We compared resource use between females and males across six sites in Argentina featuring a range of prey diversity via stable isotopes analysis of molted feathers (n=141 individuals). We then focused on two sites featuring contrasting levels of prey diversity and quanti-fied assimilated diet via stable isotopes and space use via GPS monitoring (n=23 and 12 tagged individuals). We found no clear differences in isotopic niche space, individual variation in isotopic signature, or assimilated diet between females and males. However, there were differences in foraging locations between sexes, with females apparently using areas of fewer food resources more frequently than males. Local conditions defined the dynamics of fine-scale sexual differences in foraging sites; yet, unpredictable and ephemeral carrion resources likely prevent segregation by sexes at the landscape scale. Our study highlights complex dynamics of sexual segregation in vultures and the relevancy of analyses under multiple spatial–temporal scales to explore segregation in social species.
This study was supported by Conservation Research and Education Opportunities International (CREOI), Hawk Mountain Sanctuary, the Rufford Foundation, the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison, The National Agency of Scientific and Technological Promotion of Argentina (PICT 0725-2014 and 2016-0354 BID), and Fundación BBVA (project BIOCON-08-126).