I had some unusual visitors at my feeder this week. It was a small flock of blackbirds, and they were small – not nearly the size of a grackle and smaller still than a starling. They were brown headed cowbirds, but their heads weren’t dull brown as I remember from spring, but almost a burgundy. Their jet-black feathers shimmered with streaks of neon purple. They were quite lovely.
I don’t recall ever seeing a flock of these birds, just one or two, here and there. I read that they do migrate to the south, sometimes as much as 500 miles, so this was likely a flock of cowbirds from Pennsylvania or New York just heading south.
Cowbirds are not beloved among birdwatchers. The females actually lay their eggs in the nests of other birds. They watch closely for other nesting birds and when they see a nest that’s temporarily unoccupied, they swoop in and lay an egg – more if other opportunities arise. Most other birds will raise the alien cowbird chicks, a few, like robins, will not.
Birders say that these predatory behaviors in cowbirds could slow the evolution of rejection behaviors and further threaten populations of some of the greater than 100 species of regular cowbird hosts.
Interestingly, cowbirds got their names many centuries ago as they followed the great bison herds feeding on the insects flushed from the grass and weeds as the herds moved through.
I expect to see a few cowbirds this spring as it seems there are always a pair around, but I will make sure they leave the bluebird nests alone.