My favorite book as a child was this.
Ever read it? It’s about a young bird that hatches in the nest and its mother is no where to be found. It goes up to anything and everything asking “Are you my mother?” (fantastically original title here). In the end, it does meet its mother and discovers that she had been out collecting food for it all the while. Totally sweet, right?
I don’t study birds, though I am in a department that is immersed in bird research and that is highly interconnected with the Lab of Ornithology. Oddly juxtaposed with this sweet little bird story, there is a behavior found in some birds that gives me pause. A behavior so horrific it’s hard to believe it exists in nature.
‘Are you my mother,’ this large cuckoo is asking? Certainly not. But the reed warbler photographed here is none the wiser.
This is not normal behavior, by the way. Birds don’t go out of their way to forage and collect food for someone else’s kids. Yet, that’s exactly what has happened here to this reed warbler. It has been parasitized by a cuckoo, which has laid its egg in her nest to avoid the costs of a) making its own nest and b) taking care of its own young. This, my friends, is brood parasitism.
There are many different flavors of brood parasitism. One key distinction is who these brood parasites target. Most of them are specialists – they dump their egg or eggs in one or a few host species’ nests. Some of these brood parasites, however, are generalists – they dump their egg or eggs in just about any nest they can find. The brown-headed cowbird has over 200 known hosts. I think this this alone should classify it as the world’s biggest asshole bird.
But I would be wrong. THIS is the world’s biggest asshole bird.
You may wonder why this is EVEN ALLOWED!?! Who are these ‘dumb’ birds that can’t even recognize their own offspring?
I want you to put yourself in the talons of a host bird. You’ve seen the enemy flying around your home. Maybe you suspect they’ve dumped an egg or two in your nest. What are you options? Will you do nothing or get rid of suspect eggs? Think about this problem in terms of the costs and benefits for your behavioral choice.
What costs might you pay if you do nothing? Raising the young of others, likely at the expense of your own offspring. What are the costs if you destroy some eggs? If you make a mistake, you may be getting rid of your own kids!
Similarly, the benefit of doing nothing is to avoid the mistake of killing off your own. And if you decide to destroy an egg and it happens to be the parasitic egg, then you reduce your chances of raising young that are not your own AND maintain your offspring and future lineage.
Such are the behavioral decisions of a brood parasite host. May you never think of the sound of a cuckoo clock the same way again.
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