The Cowbird

Nature is full of wonders, and we can learn many lessons from it. Remember what King Solomon, or one of his research assistants, said.

“Go to the ant, O sluggard: consider her ways and be wise.

Without having any chief, officer, or ruler,

She prepares her bread in summer, and gathers her food in harvest.”

Not all of the lessons from nature are good, of course.  After all, we are not urged to consider the alligator, who eat their young, The cowbird is another creature we do well not to imitate.

The cowbird, we are told, lives on a diet of insects, especially those that are stirred up by cattle as they move around.  This is a great way to find bugs, but there is a problem.  Since herds of cattle are always on the move, the cowbird also has to be on the move.  This creates a severe day care problem for creatures that build nests to raise their young.  Penguin parents solve this problem through great self-sacrifice on the part of both parents.

Mama cowbird, however, has found a much easier solution.  She watches other birds, and when another bird is nesting, the female cowbird lays her eggs in its nest.  The host birds are “stupid” enough to raise the baby cowbird (this is not a voluntary adoption – the cowbird is bigger than its hosts, so it is rather like adopting a gorilla), who often bullies their own chicks and hogs all their food.   The Burgess Bird Book for Children, from which I learned about cowbirds long ago, tells an anthropomorphized story about Sally Sly the Cowbird here.  Thornton W. Burgess was born in the 19th century and  apparently did not approve of the cowbird’s antics, or of the false compassion of the host, but he did not know the whole story either.

With more modern scientific research, we find that maybe the host birds are not so stupid.  Hosts who accept the cowbird eggs are “left alone” by the cowbirds, and some of their young might possibly survive growing up with their bullying big sibling.  But for hosts who push out the cowbird eggs, an “unfortunate accident” often occurs to the host bird’s nest.   A little scientific sleuthing suggests that the parent cowbirds are at fault, as the following article suggests.  (Only the abstract will load for me:  I think the article is behind a paywall.)

Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs.

…Here we present experimental evidence of mafia behavior in the brown-headed cowbird (Molothrus ater), a widely distributed North American brood parasite. We manipulated ejection of cowbird eggs and cowbird access to predator-proof nests in a common host to test experimentally for mafia behavior. When cowbird access was allowed, 56% of “ejector” nests were depredated compared with only 6% of “accepter” nests. No nests were destroyed when cowbird access was always denied or when access was denied after we removed cowbird eggs, indicating that cowbirds were responsible…

Often I hear the birds singing and squawking, and I wonder what they are trying to tell each other.

In the case of the cowbird, they might be saying, “Nice nest you got there.  It would be terrible if something happened to it.”


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