Habitat when foraging does not explain temporal segregation by sex in a breeding seabird

Abstract

Segregation by sex can allow partitioning of resources in time, space, or both. Little, however, is known about causes of sexual segregation, especially in species with little to no sexual size dimorphism. Female and male thick-billed murres (a seabird, Uria lomvia) use habitat differently at subpolar latitude, and they temporally and spatially segregate by sex across the diel cycle throughout their range, despite the sexes being of similar size. Here, we exploit the continuous light of polar summer and the presumable absence of diel vertical migration (‘DVM’) of prey at high latitude to elucidate whether the murres’ differential use of habitat when foraging at subpolar latitude was a cause or consequence of their spatial and temporal segregation by sex. We used biologgers (time-depth-temperature recorders [‘TDRs’] and global-positioning-system loggers [‘GPSs’]) to investigate temporal and spatial segregation of males and females when foraging, stable isotope analysis to assess diet, and morphometrics to assess size. Our results indicated that thick-billed murres’ temporal segregation by sex continued despite no spatial segregation and despite similarities among the sexes in foraging habitat and diet. This suggested that segregation in murres was probably caused by social mechanisms or ecological mechanisms other than foraging during biparental care. The results also suggested that the temporal segregation caused the differential use of habitat when foraging at subpolar latitude because the foraging differences disappeared when the light–dark cycle attenuated during polar summer. Our results therefore motivate further investigation of the diel behavior of murres and the cause of their sexual segregation.