Helping behaviour in brown hyenas.

The degree of relatedness between individuals is one of the primary factors influencing nonparental aid or 'helping behaviour'. However, in the field it is often difficult to determine precisely the familial relationships between helpers and recipients, and thus to assess the relative benefits of helping. Here we describe the results of a 7-yr study of brown hyenas in which most kinships were known, and report asymmetries in helping among clan members according to sex and relatedness. Natal males emigrate more often than females and provision cubs less frequently. Females provision young as distantly related as second cousins, while males provision half sibs, but not cousins. Such discrimination in nonparental aid between relatives has not been previously reported in large mammals other than primates.