Bird of the Week 8/3 - 8/7

This week’s bird is the: Brown-headed Cowbird

1. The Brown-headed Cowbird’s most famous characteristic is that it is a brood parasite – meaning it lays its eggs in the nests of other “host” birds.

2. This is a tremendous evolutionary life hack. Raising young is costly and dangerous, so laying your eggs in another nest and then peacing out is a pretty awesome strategy. But this bird’s savagery goes further than just laying an egg and then leaving. They have their ways of taking out the competition (i.e. other nestlings)…

3. For one, cowbirds will often cannonball their eggs on top of the already-laid eggs of their hosts. They perch up high, lay their big, fat eggs, and as those parasite eggs approach terminal velocity they make impact and smash the (usually smaller) eggs of their host.

4. But wait, there’s more! The adult cowbirds will often then go in and just toss one or two host eggs from the nest for good measure. This seems much simpler and I’m not sure why they really need to do the cannonball thing…

   

5. And potentially my favorite bird fact of all time: if the host bird recognizes and rejects the cowbird egg from the nest (i.e. tosses it out), the cowbird will often come back and destroy all the host’s eggs. This is referred to in the scientific literature as “mafia behavior” – no joke!

6. But before you judge the cowbird too much, just remember that it is a bird-eat-bird world out there and evolutionary strategies exist because they allow species to persist, whether or not it aligns with our human vies on morality. And this isn’t nearly as bad as screwworms, zombie-ant fungus, or even the “butcherbird” IMO. To learn more about brood parasitism and the Brown-head Cowbird click here and/or here.

Have a nice week, and remember, never reject a cowbird egg!