Bird Watcher's General Store

Male Cowbirds Defend Their Females - 08/09/02


Dear Bird Folks,

For the past few weeks I've had a male cowbird attacking my solar oven. I understand that birds often fly at their reflection to defend their nesting territory, but why would a cowbird, who doesn't even build a nest, be defending its territory?

Jeff, W. Harwich

You see, Jeff,

Cowbirds have long been supporters of the utility companies. Most cowbird portfolios are heavily weighted in utility stock. The thought of you getting free power is very upsetting to them and they will do whatever they can to stop you.

Many of us know that cowbirds, don't build their own nests, they lay their eggs in other birds' nests. They then let the victim bird feed and raise their chick. In the bird world, a bird that raises another bird's offspring is called a "host bird," in the human world they are called nannies. You are right Jeff, cowbirds don't build their own nest, but that doesn't mean they don't defend a territory. A cowbird territory can be huge, 10 acres or more. Cowbirds need to find a lot of nests because they lay a lot of eggs, up to 40 a season. However, their success rate is low, only about two or three make it to adulthood.

Most of the territory defending is done by the female. The male doesn't defend a territory, but does "guard" a female. The male cowbird will attack any intruding male cowbirds or solar ovens. Since you are seeing a male cowbird, Jeff, my guess is he has some hot babe close by.

The female cowbirds often keep a low profile within their territory. They sit for hours watching all the other birds, hoping one will give away its nest site. If she finds an unguarded nest, she will swoop down and with lightening speed remove an egg of the host bird and drop in one of her eggs. It ususally takes her only a matter of seconds to lay a single egg and move on.

The idea of having someone else raise your kids sure sounds appealing, at least it does to me, but we should not think of the cowbird as lazy. Laying 40 eggs in a season is no easy task. Producing eggs takes a huge amount of energy. By contrast, most of our cardinals probably lay less than 10 eggs per season and they don't have to find a new nest for each egg. Plus, cardinals don't have to deal with the guilt that comes with dumping 40 of your own kids on strangers.

It should also be noted that a young cowbird is not aggressive toward its fellow nestlings. Oftentimes, the host bird's real offspring do quite well, except, of course, for that one egg that got tossed out. That egg is well on its way to becoming a prominent member of the food chain.

You hear me say this every week, but once again we find something in the bird world that is so amazing that it defies explanation. How does a young cowbird, that is raised by say, a pair of bright yellow warblers, somehow figure out that it isn't a warbler? How does it know that it should, shortly after learning to fly, leave the company of colorful tree-loving warblers and move to the ground with all the other dull brown cowbirds? This ugly duckling has no idea what it looks like, it doesn't have a mirror or video of itself to watch, yet it finds its way to its own kind in a few short weeks after hatching.

Thanks for the question, Jeff, and thanks for saving resources by using a solar oven. If you ever need anyone to sample what you cook in that oven, I'd be happy to help you out.



Artwork by Catherine Clark


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