Adoptions and offspring swapping stun kangaroo researchers

From PhysOrg:

Kangaroos adopt. It doesn't happen often, but to the astonishment of biologists at Wilsons Promontory National Park in Australia, sometimes a mother bends forward, opens her arms and invites someone else's youngster to hop into her pouch. Once made, the mix-up endures, lasting through the remaining weeks of “pouch life” and on during months of the “young-at-foot” stage, when the growing juvenile kangaroo continues to nurse. “It's a complete surprise to us,” said Graeme Coulson, a zoology professor at the University of Melbourne in Australia.

Coulson described the baby swapping — in which two mothers end up with each other's young — this month at a joint meeting of the American Society of Mammalogists and the Australian Mammal Society in Portland, Ore. Although rare cases of marsupial fostering have previously been reported in captivity, and biologists have used fostering in breeding programs, this appears to be the first documented report of spontaneous adoptions in the wild, said Roberta Bencini, vice president of the Australian Mammal Society and professor of animal biology at the University of Western Australia. “That's really quite an unusual discovery,” said Bencini, who was not involved in Coulson's research. “I would like to find out why.” So would Coulson. The exchanges seem to have no apparent benefit for the mother, who squanders her own resources on another's offspring, Coulson said. His best guess is that the swaps are simply an error by one mother later compounded — or perhaps just accepted — by another.

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