Non-offspring maternal care should be rare due to the high costs of raising offspring, particularly lactation, but nonetheless occurs in a variety of taxa. Misguided parental care, associated with recognition errors and/or in attentiveness by lactating females, has been hypothesized as an explanation for all olactation in mammals. In an
extension of this hypothesis, we suggest that milk-stealing is parasitism instigated by non-filial offspring, and that maternal behaviour is of secondary interest in an evolutionary context if she is unaware of the interaction. We provide evidence for frequent milk-stealing attempts by
Subantarctic fur seal (Arctocephalus tropicalis) pups, including an example of sustained non-maternal care (4 three months) for one pup during the confirmed absence of his mother, leading to a weaning massequal to the population mean. We also present only the second account of fostering/twins
in the species at this locality. We suggest that rather than the hitherto suggested rare and anomalous behaviour, milk-stealing behaviour (while not always successful) is common.