Cowbirds are Jerks

Given that I have a science background, I sometimes find myself interested in the social behavior of animals and how these behaviors have evolved.  I learned that loons were big jerks, but Canadians still seem to love them anyway.  They just hide the fact that they are jerks by looking and sounding pretty (I’m sure this seems vaguely familiar to some of you).

Today I was watching a cowbird through binoculars.  As it turns out, rather than make the effort to build nests, cowbirds sneak in and lay their eggs in the nests of other birds when they aren’t watching.   Apparently for passerine birds, cowbirds lay eggs at unusually high rates, like at chicken-level egg laying rates, to compensate for high egg mortality.  And, rather than spend effort incubating eggs (since they hijack other nests) the females sometimes hang around their innocent victims’ nests like psycho-moms, watching to see what happens to their eggs.  As if this wasn’t crazy enough, two scientists, Hoover and Robinson, discovered that cowbirds, like cuckoos, will retaliate and destroy the eggs of the host birds if the host birds reject the cowbird eggs.  Jerks!

Even better, if the eggs aren’t rejected by host parent or parents, the cowbird chicks will hatch earlier, grow noticeably bigger and create much more noise than the host bird chicks, giving them an advantage to get more food.  Once fledged, cowbirds live around cattle, eating insects that are stirred up by them.  That’s right; cowbirds even take advantage of the easy access, all-you-can-eat buffet provided by cows.

Next time I meet a sponging, lazy, vindictive human who can’t stop breeding, I’ll try to remember that the behavioral niche for jerks evolved a long time ago.  Nature has developed many creative methods of ensuring the survival of a species.


Brown-headed Cowbird, from You can recognize it based on its distinctive hat, boots and belt buckle.



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