Put simply, babies are parasites. Don’t believe me? Just look at your own life. For your nine months as a fetus, you sat inside your mom literally doing nothing, not to mention the fact that you were connected to her via an umbilical cord siphoning away all her nutrients. Then you were finally born, but you were still taking your mom's nutrients because she had to produce all that milk that you sucked out of her chest. And you cried, puked and pooped yourself and didn’t even say thank you. Then you were a kid going to school, and you just used up your parents' time and money in the form of rides to school and keeping your lunchbox full. Now you’re a big adult, except your parents may still pay for your college tuition, which in this day and age, might be even worse than all those previous things combined. What’s my point? Raising kids is damn difficult. And that’s why some birds just avoid it all together.
Brood parasites are birds that lay their eggs in the nests of other species rather than building their own. Evolutionarily speaking, it is an absolutely genius strategy. Why waste time and energy incubating and feeding newborn babies when you could just have some other bird do it for you? Imagine if your mom had just dropped you off at some other lady’s house and that other lady raised you. Then your mom would have effectively succeeded in passing her genetic material to the next generation while expending zero energy in the process. This is exactly what female birds like the brown-headed cowbird do every breeding season following an easy, three-step process: Find a nest, lay the egg(s) and let the offspring outcompete the other babies.
Many people hear this and think, “Why doesn't the host mom get rid of the egg from the brood parasite?” Well, it’s complicated. Some host species are stupid and simply cannot discern the difference between their own egg and the parasite egg. Sometimes, the parasite eggs look so similar to the host eggs that it’s difficult for even the most astute of host parents to differentiate between them. And other species know there’s a parasite egg in their nest, but they just accept it. Some brood parasites will destroy a host nest if they dispose of the parasite egg, and as a result, host species have adapted to simply accepting the parasite eggs because that’s better than having no offspring at all.
Once the eggs have hatched, it can get ugly. Many parasite nestlings instinctually murder all the other nestlings in the nest so that they can claim every morsel of food brought to them by the host mom. Even when these mini-massacres occur, the host mom still brings the parasite nestling food — that’s what their motherly instinct drives them to do!
Though brood parasitism may be exceptional biologically speaking, it’s terribly depressing from an emotional perspective. Imagine those baby cowbirds growing up without parents. They probably never feel love … And I bet you some of those mama cowbirds wonder if there are more to babies than just plain-old energy depletion.
Love,
Henry
