Sex-specific migratory behavior in a marine predator results in higher risks to females

Abstract

Protecting migratory species requires knowledge of their distributions throughout the year. Spatial or temporal segregation of females and males during part of the annual cycle complicates conservation measures and can lead to sex-biased mortality. Females and males of many seabird species use separate areas during the nonbreeding season, and sex-biased bycatch in fisheries is common. We satellite-tracked 8 female and 8 male post-breeding adult Magellanic penguins Spheniscus magellanicus, including 7 pairs, from Punta Tombo, Argentina, during their fall northbound migration. Our results agreed with recent studies from other colonies, and provided more accurate locations than the geolocator tags used in those studies. Females stayed 47 km closer to shore than males. On average, females and males reached similar latitudes from northern Argentina to southern Brazil. Females tended to stay farther north, however, with some males heading south by June. Body size did not influence how far offshore a penguin migrated, when controlling for sex. On average, females left the colony 2 d before their mates, and did not encounter them at sea. The mean distance between mates at sea was more than 350 km. Females are likely exposed to fishing gear and pollution more than males because the females stayed closer to shore and stayed farther north than males. Migratory routes varied among individuals. The large area that penguins use during their nonbreeding season makes protection of the population difficult.