I love how people think of some birds as “good” and other as “bad”. They feel that some birds are actually nice and friendly while others are mean and ill-spirited. They even go as far as thinking that some birds are welcome at their feeders while others are not. Well, I’m not one of those judgmental people. I like all birds. In fact I have never met a bird that I didn’t like.
The Brown-headed Cowbird (Molothrus ater) is one of those birds that many people don’t like and I might go as far as to say that some people hate this bird. Again, I don’t understand this kind of thinking because I am truly amazed by this bird.
So why do some people hate this bird? Let me explain. The cowbird is a nest parasite. The female doesn’t build her own nest to lay her eggs in. No, instead, she finds the nests of other birds and relies on these “host” families to incubate and raise her young. During the breeding season a female cowbird will mate then slip off to parasitize other nests. More than 220 species of birds are parasitized by cowbirds. Of these about 140 species actually knowingly incubate and raise the young cowbirds.
For years naturalist like myself and researchers have wondered why do these birds knowingly raise a young cowbird to the detriment of their own young. Studies indicate that birds such as warblers that raise a cowbird chick have on average 3 of their own while warblers who don’t have a cowbird chick raise 4 of their own so its obvious that the warbler is not benefiting from hosting a cowbird.
A recent study which was modeled after a study originally preformed in the 1940’s gives us some insight into this conundrum. It turns out that cowbirds use mafia like tactics to insure they young are raised and it goes something like this. When a female cowbird finds a nest she will deposit one of her own eggs then she removes one of the host birds eggs. By the way, a female cowbird can lay up to 40 eggs in a single season which must be some kind of record because most birds usually can produce less than ten.
In the study the researchers took the cowbird egg out of some of the warbler nests while in other nests the cowbird egg was left. In 56 percent of the nests where the cowbird egg was removed, the female cowbird came back and destroyed all of the warbler’s eggs and nest thus sending the message “if you don’t raise my baby, I will take out your entire family”. In the nests where the cowbird egg was left, only 6 percent were depredated.
So this leaves the host birds with not much of a choice, either raise a cowbird chick or nothing at all. Now that is what I call a fascinating story. Until next time…