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ambience: nestling, begging
When you picture a parasite, what probably comes to mind is probably not a small, harmless-looking bird. It turns out, though, that one of North America’s most common feathered friends is a serious freeloader. I’m Jim Metzner, and this is the Pulse of the Planet. We’re listening to the sound of baby cowbirds in a nest. But they’re not begging for food from their cowbird mother, or any other relative. Cowbird females lay their eggs in other species’ nest. And with these incubating eggs come plenty problems for the chosen hosts. Mark Hauber is a behavioral ecologist at Cornell University.
“Cowbirds have a short incubation period: they hatch in about ten, eleven, twelve days. And that’s really short for any bird species, but especially short for some of the hosts that they parasitize.”
The cowbirds’ early development appears to be an evolutionary adaptation to ensure that they get the attention and food of the guardian bird.
“Because the cowbird hatches earlier than most of the host nestlings, the parents have to start providing for the young cowbird that begs vigorously soon after it leaves the broken eggshells. And because of that, the host parents spend less time incubating on the nest, which means lower temperatures in the nest and even failed development for some of the host eggs. Sometimes though the, the incubating parent will stay on the nestling and the other parent will provide for the young cowbird. In either case the cowbird will have a size advantage over any of the host nestlings it has to compete with for food.”
Cowbirds have a lot to tell us about the relationship between genetics and the environment, we’ll hear more in future programs.
Pulse of the Planet is presented with support provided by the National Science Foundation. I’m Jim Metzner.
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