Differences between incubating female and male Imperial Cormorants in multiple trophic niche dimensions

Abstract

Sexual segregation in feeding ecology is widely documented in seabirds. The Imperial Cormorant (Leucocarbo atriceps)shows sexual differences in diet composition and feeding behaviour but no studies have yet simultaneously characteriseddifferent dimensions of female (F) and male (M) trophic niches during the incubation period. Patterns of sexual segregationin the trophic niche were evaluated through the simultaneous analysis of feeding areas, diving depths, temporalfeeding patterns and isotopic niche during the late incubation stage of 2019 at Blanca Mayor Island (44°46′S, 65°38′W),Argentina, using GPS loggers (5 F, 3 M), time-depth recorders (5 F, 5 M), and stable isotope analysis of plasma (δ15N,δ13C) (5 F, 5 M). Over a period of three consecutive days, 20 foraging trips and 2952 dives were recorded for females,while 11 foraging trips and 878 dives were observed for males. Both sexes fed within the bay where the colony is located,but females fed in shallow areas to the north and south of the colony and males in areas south of the colony in deeperwater. Although sample size was limited and used a small coastal area, a clear spatial segregation was found betweenboth sexes. Females and males also showed differences in the timing of feeding and in the number of dives and maximumdepths, although there was no difference in the isotopic niche in the short period of time evaluated. The results improveour understanding of the ecology of this species in the region and will contribute to future studies on the role of each sexin coastal food webs.