Now pretend that you are the thirdborn in your little family; your older brothers hatched before you, and even if that means just a difference of a few hours, they’re still technically “oldest.” Maybe number one is the most aggressive when Mom comes back with food. Maybe middle child has good genes on his side, and can simply muscle his way to the front of the line when the folks regurgitate breakfast. Maybe you’re all the same size but two of you are just more timid, more susceptible to being bullied. Either way, anyone looking in would be quick to notice that a clear “pecking order” is forming, based on size and strength. The most fed gains the most strength, after all. Big deal, though, right? There’s no harm in being the runt of the litter, right? The big deal arises one morning when you wake up to find that your biggest brother has murdered your other sibling in a dispute over food, and guess what? You’re next, runt.
It sounds brutal, and it is. Biologists have termed it, “Cain and Abel Syndrome.” Nestling raptors will, on occasion, kill their weaker siblings in order to establish a monopoly on incoming food. You might question the biology behind it: does killing your nest-mates really help your species survive? Mated raptors have every reason to want all of their offspring to survive, because that maximizes the chances that their specific genes will be carried on. But the birdie Brutus who kills his kin has an entirely different motivation: he wants to survive, and the more food he gets, the better. He doesn’t directly benefit if his siblings survive to pass on their DNA. His behavior isn’t all that different from a male lion who takes over a rival’s pride and then kills all of the cubs; he wants to pass on his legacy, and his alone. This little Brutus isn’t necessarily thinking about fatherhood; after all, he’s just a baby himself. What he’s thinking about is survival, and survival for any animal equals: food. His instincts tell him that he needs to eat as much as possible in order to thrive, and those other mouths are just getting in the way. This doesn’t always happen, by any means, but it has been documented in raptors around the world. In some cases, especially where some kind of distinct advantage has been conferred to one sibling over another, fratricide takes place. Cain kills Abel, or in the case of our nest, Abel and their little brother.
Is there anything positive to be gleaned from Cain and Abel Syndrome? Eagles are most likely to demonstrate “Cainism,” as it is sometimes called. They’re the biggest predatory birds, after all, and their babies will need the most food, sparking the most competition. The smaller you go down the raptor line, the rarer it becomes; if you are an American kestrel, then you probably have nothing to worry about. Beyond that, it is an interesting, though brutal, fact of life. The wild world operates by a different rule set; the fact that one sibling could kill another in order to get more food is no different than a pair of mated red-tailed hawks abandoning a compromised nesting site and simply starting over someplace else. It’s nature’s pragmatism at work. It’s survival, whether in terms of genetic legacy or simply on a day-to-day scale. One bright spot? Some researchers working with critically endangered eagles have adapted a technique that they call “Saving Abel”: it “involves removing the younger chick from the nest, rearing it in captivity until it is big enough to fend off attacks, and returning it to its nest.” Sometimes they’ll take Abel and place him in a nest with eagles that have, for whatever reason, laid infertile eggs. Think of it like an adoption: birds really can’t rationalize the difference between a baby that comes from an egg and a baby that just shows up one day. They assume it’s theirs and start caring for it. For endangered species, every offspring is needed, and keeping the Abels of the world alive means one more bird who can help give their kind a fighting chance. It isn’t much, and in practicality it is only applicable for certain species in certain circumstances, but for those particular Abels, it definitely beats the alternative.
1. Weidensaul, Scott, The Raptor Almanac: A Comprehensive Guide to Eagles, Hawks, Falcons, and Vultures (Guilford: Lyons Press, 2004), 246.