by Stan Tekiela
June 19, 2009
Photo by Stan Tekiela©
Nature is a strange and wonderful thing. It is so incredibly complex that science has yet to wrap its understanding mind completely around it. Yet nature is simple enough to be well balanced and takes care of itself without help from people. To see an example of this duality just take a look around your own yard. Have you ever seen a tiny adult bird feeding what appears to be a very large baby bird? That is what I’m seeing in my yard this week.
So what’s going on with these smaller birds feeding larger baby birds? These Baby Huey’s couldn’t possibly be the offspring of these small adult birds? Could they? Well the answer is yes and no.
The incredible story goes like this. There is a bird called the Brown-headed Cowbird. They’re called this because the male has a brown head and they are commonly seen around cows. It is a common native bird that is a member of the blackbird family. The cowbird has the most unusual nesting habits. Or should I say non-nesting habits. You see, the female cowbird doesn’t build her own nest. Nor does she incubate her own eggs—EVER. Rather she is an expert at finding the nests of other birds such as sparrows and warblers where she will lay her eggs in a “host” nest.
While the resident mother is away from the nest the female cowbird slips in and lays one of her own eggs. The egg laying process only takes a minute or two so the cowbird is in and out quickly and often unnoticed by the nest owner.
Now comes the interesting part. Cowbirds lay their eggs in up to 200 species of “host” bird’s nests. Some of these birds will reject the cowbird egg by removing it. Some will simply build a new nest right over the top of the old nest with the cowbird egg in it. However many will accept the cowbird egg as their own and raise the cowbird young as if it were their own. Are you starting to see the picture?
The cowbirds non-nest building behavior is called parasitic nesting. It relies on host birds to build the nest and raise their young often to the detriment to their own natural babies. There are about 750 species of parasitic birds worldwide. The Brown-headed Cowbird is the only one found in our region.
I think most people would automatically jump to the conclusion that the cowbird is a bad bird. After all how could it be anything else? Well, the few studies that have been done might indicate the opposite. For example, in one study, a hundred host nests that had cowbird eggs where monitored. In half of the nests the cowbird’s egg was removed and in the other half the eggs were left. Of the nest where the cowbird egg was removed move than half of the nests were destroyed. Of the nests with the cowbird eggs less than 20 percent were destroyed. The thinking is, the cowbird adults are affording some level of protection for the nest and eggs as a reward for allowing the cowbird egg to remain. After all the cowbirds have a vested interest in keeping the host nest and eggs safe so their own babies will survive.
Brown-headed Cowbirds have been around for hundreds of thousands of years, perhaps millions of years and as far as we know their parasitic behavior hasn’t harmed other species in a balanced undisturbed habitat. So in fact the reason we think they are a bad birds has more to do with our own sense of fair play and nothing at all to do with actually being a bad bird.
I find myself fascinated at the fact that cowbird babies grow up with host parents who don’t look or sound like cowbirds at all. This gets me thinking, how does a baby cowbird grow up to know that it is a cowbird and not a sparrow or warbler? How does the cowbird learn to sing the right song and find the right mate? The answer is, no one knows. These are just a few of the mysteries of the cowbird world and I think the most interesting aspect of this much maligned bird. Until next time…
Column List | Back to top