Cowbirds are like upside down Grackles: Blackbirds with rainbow iridescence, but a Cowbird’s rainbow runs in the other direction, from tail to head. His Squeek is Grackley but sounds more like a ‘glug, glug, squeee’ than ‘Creek, Creek, squeeeeeek, and Cowbird voices are much squeekier.
These guys are famous. They used to be called Buffalo Birds because they ate the insects that live on Buffalo and were part of the migrating buffalo ecology that moved around the content but we killed all the Buffalo. (There were 60 000 000 of them and colonizers did it on purpose to hurt native people) The Buffalo were replaced by domestic Cows and the Cowbirds adapted.
Part of the story is that the birds had to keep moving to keep up with the Buffalo so they stopped nesting. There just wasn’t enough time to make a nest, lay, brood and raise fledglings before the Buffalo wandered off, so they laid their eggs in other birds’ nests and left them to be raised by strangers.
It’s not exactly true, but it’s a good story. The thing is that Cowbirds don’t abandon their babies. The part where they don’t ever make their own nests is true, they always lay their eggs in some other bird’s nest and often in several other birds’ nests like the Easter bunny does. Sometimes the host is a bigger bird, sometimes a much smaller bird and the unconsenting adoptive parent is stuck feeding a baby who might quickly grow up to be much bigger than them and who will probably eject the other babies from the nest. But Cowbirds don’t do it because they have to go, they stick around.
This behavior is called brood parasitism and there are people who don’t like it. If you find a nest containing the egg of a brood parasite your eye might be able to recognize it. The host bird might not, but then again she probably knows exactly what’s going on so just leave them all alone. If you remove the Cowbirds’s eggs Mrs. Cowbird will notice when she comes to check on them. If her eggs are gone but the host’s remain, she will remove/break the other eggs. (What the heck are you doing looking in nests anyway?)
This behavior is evolutionarily advantageous to Cowbirds because it is usually not a human who does the eviction, it’s usually a host parent who notices and removes the foreign egg, but a mother Warbler who is able to see the difference between the eggs and who is inspired to respond by removing the Cowbird egg will not pass these traits on to her offspring because those offspring will not hatch, having been broken by the Cowbird. So if you remove the Cowbird egg to protect the host you actually ensure that the other eggs will also die. What will likely happen next is both sets of parents will start laying eggs again, which is very energy expensive. They will likely also build a new nest in a new site because this location was a failure. So much work to replace a perfectly good nest that you sabotaged. Vigilanti Cowbird egg thieves don’t help the host, they hurt them more.
Do we have the authority to decide what species lives and dies? The choice of a Robin over a Cowbird is based on human values: the idea that no one should ever have to work to support someone else’s kids. Wait, that’s what human’s believe? That’s a pretty low down value. To let this value drive you to kill things is disgraceful. Things exist in fabulous symbiosis. Ecology is magical clockwork. If you take out the cogs that you don’t like the magic will stop ticking.
The Cowbird story continues: baby Cowbird hatches and grows up in a nest of birds that look, sound, smell and behave totally different. It must be weird. But they are not cut off from Cowbird culture. When they are big enough to fly, but still living in the nest they wake up in the middle of the night. The rest of the family is sleeping. There is the sound of Cowbirds singing off in the distance. The adolescent Cowbird sneaks off to make Cowbird friends and play Cowbird games and learn Cowbird things and then climbs back into the nest before any one else wakes up.