New research by Auckland University scientists has shed light on the breeding habits of New Zealand's nationally endangered southern right whale population.
They say most of the whales born near the remote sub-Antarctic islands were fathered by males from the same local population.
That has surprised them, because mammals normally disperse from their place of birth to seek new mating opportunities.
The Department of Conservation and Oregon State University helped with the study, which involved the collection of DNA samples from 34 mother-calf pairs, and more than 300 males, over a 15 year period.
Auckland University says the finding is good news for the overall genetic diversity of the species, but could put local populations at risk because of in-breeding.