30 January 2013

Wet nurses in the whale world

Caring for the young is a global phenomenon, as is survival of the fittest. Social animals care for their young, usually within a family (or social) unit. What would stand out of the ordinary is when a family unit of one species cares for the young of other species. Mixed-species units are often observed during feeding migrations, notably of species that go after the same type of prey. But mixed-species family units are rarer.

A dolphin with a spinal deformity mills with sperm whales.
Photograph by Alexander Wilson and Aquatic Mammals

Recently, researchers in the Azores observed a social unit of  sperm whales which adopted a deformed adult bottlenose dolphin. One of the possible explanations for this rather rare behavior is that the dolphin is behaving like a sperm whale calf. Its deformity forces it to stay at the surface of the water, a behavior typical of whale calves which permits nursing females of the family unit to breast feed their young (Whitehead 2009). As family units often consist of females and their calves (Whitehead 2003), communally caring for their young (Best et al 1984), the adult (and small) bottlenose may have been taken in as a calf albeit of another species.

Best, P.B., Canham, P.A.S., and MacLeod, N. (1984). Patterns of reproduction in sperm whales, Physeter macrocephalus. Rep. Int. Whaling Comm. 6(Special Issue), 51-79.
Whitehead, H. (2003). "Sperm whales: social evolution in the ocean." University of Chicago Press, Chicago.
Whitehead, H. (2009). Sperm whale, Physeter macrocephalus. In Perrin, W.F.; Wursig, B.; Thewissen, J.G.M. 2009. Encyclopedia of Marine Mammals, Second Edition. Academic Press: London. 1316pp.

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