Dear Bird Folks,
I recently introduced a friend of mine to birding and she is just full of questions. When I told her that a few cowbirds had visited my yard, her first question was, “Why are they called cowbirds?” I have researched David Sibley and Roger Tory Peterson, with no success. Help!
– Ann, Simsbury, CT
Who did you research, Sibley and Peterson? I don’t know who they are, but I’m sure they’re important to somebody…perhaps their families. When it comes to birding info, look no further. I have the answer you’ve been searching for. Cowbirds get their name for being one of the few birds that feed their babies milk. Each spring cowbirds collect little droplets of milk from the udders of nearby cows. Using their large beaks as containers, the birds then carry the milk to their hungry nestlings. The nutritious milk helps the babies grow up healthy and strong. Actually, none of that is true, but I think you should tell your friend that story anyhow. If she believes it, let me know. It will give me a head start on my next April 1st column.
While cowbirds want nothing to do with milk, they do like cow-ish creatures. Historically, cowbirds followed the great herds of bison that once roamed this country (before the settlers thought it would be cool to kill them all). Why would the birds want to follow buffalos? I’m mean, have you seen what’s behind those stinky things? It turns out that the birds really don’t have a use for the buffalos themselves, but they like to feed on the insects that herds stir up as they go. The phrase “as they go” is important because there’s a theory that the moving bovines have influenced the cowbirds’ breeding strategy. Let me explain. It takes time for the cowbirds to stop and raise a family. But if they stop, their beloved bovines will be gone. So, the cowbirds have evolved a plan B. Unfortunately, plan B has made them one of the most disliked birds in North America. The nomadic Mrs. Cowbird doesn’t have the time to build a proper nest. Nor does she have time to incubate her eggs or raise her own kids. Instead, she drops her eggs into the nests of other birds and lets those birds deal with her kids. In birds this is called “parasitic.” In humans it is called “daycare.”
Here’s how it works: In the spring the female cowbird spends her day sitting in a tree, or on some other observation spot, and watches for another bird to pass by with nesting material. Once a nest-builder is spotted, the cowbird will secretly move in. Usually, she won’t deposit her egg in a nest until the host bird has laid an egg first. (Cowbirds may be parasites, but they still have ethics.) This generally happens early in the morning when the host bird has gone out for breakfast. And once the cowbird has laid a single egg in a nest, she is done with it. She then moves on to look for a new nest to deposit another egg in. In one season a cowbird may lay up to forty eggs in many different nests. A good question to ask is: Why only one egg per nest? Wouldn’t laying several eggs in the same nest be more efficient? No, it wouldn’t. Cowbird kids tend to be considerably larger than even the adult host birds. The smaller hosts have trouble providing enough food for one giant baby; two would be overwhelming. In addition, by distributing her eggs to additional nests, the cowbird increases the chance that at least a few of her eggs will hatch. In fact, archeologists have proof that the proverb, “Don’t put all your eggs in one basket” was written by an ancient cowbird philosopher. (Tell your friend that one, too, Ann.)
To help ensure its success, the cowbird baby tends to hatch a day or two earlier than its future stepbrothers and sisters. It also grows faster and thus can out-muscle its nest mates at the dinner table. Things really get weird when the much larger cowbird chick finally fledges and is seen around town being fed by the much smaller foster parents. Each summer customers tell me that they have a “baby bird” in their yard that is feeding a big “adult bird” that is begging. It freaks them out. (OMG! As I type this, a young cowbird landed on my feeder and was immediately fed by a pint-sized Song Sparrow. What are the odds? It was like the cowbird knew I was writing about it. Its feather-covered ears must have been burning.)
The next question is: What happens to the host’s own babies? Do they all go hungry because huge Baby Huey steals all the food? There is no doubt that cowbirds have an impact on their host birds, but not all the babies are lost. Unlike the parasitic cuckoos in Europe, young cowbirds aren’t aggressive to their nest mates. If the parents can find enough grub to go around, many of their offspring will also survive. One bird that turns the tables on the cowbird is the House Finch. House Finches are basically vegetarian and thus they feed the insect-loving baby cowbird a steady diet of seeds, which causes the intruder to eventually starve. (FYI: Don’t mess with a vegetarian.)
I’m glad you introduced your friend to birding, Ann. Birding is a great activity. It gets folks out in the fresh air and reintroduces them to nature.
BTW: I’m sure you know I was kidding when I said I didn’t know anything about David Sibley and Roger Tory Peterson. Both men are brilliant ornithologists and are extremely knowledgeable. Take it from me; I know how smart they are. Who do you think taught them?