For the Birds Radio Program: Avian Surrogate Motherhood
Changed from 4/8/87 (3:18) Date confirmed.
(Recording of a Brown-headed Cowbird)
Surrogate motherhood is a rare phenomenon among human beings, and it’s not unheard of in the bird world, either, although money is never involved. Brown-headed Cowbird mothers, for example, always bestow their children upon other mothers. Cowbirds naturally don’t trust lawyers to choose good adoptive parents–the female cowbird herself spends weeks carefully studying the nesting habits of nearby birds, and then she selects 10 or 12 couples as most suitable to incubate and raise her young.
Unlike human surrogate parent contracts, there is no legally binding requirement that the avian adoptive parents actually must raise the young cowbirds, and some adamantly refuse. Robins and catbirds invariably toss out cowbird eggs. House Wrens puncture them. Yellow Warblers often cover up a foreign egg with new nesting material and start building the nest all over. This is pathetically like throwing the baby out with the bathwater, since the Yellow Warbler’s own eggs are also buried. One Yellow Warbler made a 5-layer nest covering up 11 cowbird eggs and quite a few of its own–this was one bird that definitely disapproved of surrogate parenting.
Although cowbirds relinquish custody of their young, they do often retain visitation rights, and mother cowbirds usually remain aware of the well-being of their babies. In one instance, a cowbird mother valiently fought off a domestic cat which had attacked one of her young.
Cowbirds are back in the Northland again. The males are displaying to assert their masculinity while females size up the neighborhood to choose the likeliest areas for suitable adoptive parents.
Other bird species occasionally raise young which are not their own. In California, a pair of kestrels fed their own four young along with a baby screech owl. Apparently the female owl had laid her first egg in the nest hole before her mortgage was foreclosed by the kestrels.
One flicker adopted and successfully raised a family of starlings near London, Ontario. And a screech owl adopted a brood of flickers in a nest box, even though normally these owls eat woodpeckers! The screech owl brooded the eggs like a setting hen, and even brought the hatched-out babies a mouse to eat. Meanwhile, the natural parents decided to fight to regain custody, and flew in and out of the nest feeding the babies ants and other insects. Finally the screech owl was forced to concede that the natural parents were providing a more suitable home environment, and the predator relinquished custody. But, like any real mother, she left the flicker babies unharmed.
(Recording of a Screech Owl)
This is Laura Erickson, and this program has been “For the Birds.”