Intraspecific trophic variation in brown booby ( Sula leucogaster ) from the Southwestern Atlantic

Sexual size dimorphism in seabirds may reduce intraspecific food competition by exploiting different trophic niches by each sex. We tested the intraspecific trophic segregation between sexes of brown booby ( Sula leucogaster ) using regurgitated prey and stable isotopes ( δ 15 N and δ 13 C) from whole blood and prey muscle in Santana Archipelago (SA), in north state of Rio de Janeiro, Brazil, Southwestern Atlantic. As females are larger than males, it is expected to have a broader niche amplitude and higher trophic position than to males due to consuming a wider variety of prey sizes. Expeditions to SA occurred from June 2017 to May 2018, where 53 females, 48 males and 54 regurgitates were sampled. Overall 22 fish species were identified: 77% demersal species, of 399 prey items (54.4% demersal prey). The Relative Importance Index indicated the pelagic Chirocentrodon bleekerianus as the most important prey for females and the demersal Cynoscion guatucupa for males. Demersal fishes were more consumed than pelagic fishes; especially during winter (83% and 76% of prey mass and number, respectively). In all seasons, stable isotopes differed between sexes. Females showed larger isotopic niche than males, indicating that may consume a broader varied of prey, although trophic position ( δ 15 N) were higher in males. Thus, the brown booby population from the SA shows a trophic segregation between sexes thought the year, and demersal fish is an important part of the seabird’s diet, which may contribute to promote the niche segregation.