As winter approaches, the whales stop feeding and head to warmer, shallow waters near coasts or groups of islands. For example, populations of humpbacks spend the winter near Baja California and the Hawaiian islands. During the winter the whales do not feed; instead they concentrate on reproduction. The males produce songs which are repeated over and over for days on end. The songs probably attract receptive females that are not caring for calves that year, and also help rival males keep away from each other. Pregnant females stay feeding for longer than the other whales, and arrive in the wintering grounds just in time to give birth.