Allo-suckling in the South American fur seal (Arctocephalus australis) in Isla de Lobos, Uruguay: cost or benefit of living in a group?

Abstract

In some social mammals females feed alien offspring (allo-sucking, AS), a phenomenon rarely observed in otariids, possibly due to the existence of strict mother–pup recognition mechanisms. We studied the frequency of AS during the reproductive season in the largest South American fur seal rockery (in Uruguay). We recorded 57 AS attempts in 342 hr of observations, 26 of which were successful. Successful AS attempts represented 3.37% of all suckling events. In January most attempts were successful, while in February most attempts failed, probably reflecting a more active defence of milk by females and filial pups as a consequence of the increase in energy requirements. Females interrupted 72% of all AS attempts. We propose that allo-suckling is a benefit of living in a group that increases survival of offspring during the earliest months of life, the period of highest pup mortality.