Wings on the River: Cooperative nesting

The local Vaux’s Swifts are tiny, soot-colored birds that live mostly in the air. They nest in trees and chimneys, sticking three-inch nests of twigs together with saliva. They don’t bother with territories and may build multiple nests in the same tree.

Sometimes, three birds work together, feeding the young at a single nest. This suggests that like their close relative, Chimney Swift, they may breed in trios.

In some animal species, it’s the 1950s-style nuclear family that’s odd.

Our local Acorn Woodpeckers live in groups up to 15 strong. They work together to defend and maintain large trees, which they drill full of little holes, then jam full of acorns to eat later. Some sexually mature birds don’t lay their own eggs, instead helping relatives parent — like childless uncles and sisters who’d rather just help the village kids — bringing food and defending the granaries. Flocks of 7 to 8 birds have the best breeding success.

Apparently, nature encourages this kind of thing. If good territories aren’t available, scientists say, a bird might as well help pass on its sister’s genetics, which are close to its own.

Which is another way of saying, it takes a village to raise a chick.

Even in songbirds that mostly nest in neat male-and-female pairs, genetics show that most consort with multiple other partners, then raise a nestful of chicks only some of whom may be related to their social partner.

Some are particularly enthusiastic about it. According to researcher Donald Kroodsma this may be why some birds, like buntings, keep singing long into summer when everybody else has gone silent: just because they’ve all got a social partner and kids doesn’t mean anybody stopped courting.

Also ... In the 1970s, researchers partly funded by the National Science Foundation in California first realized up to 14% of the western gull colony they were studying was same-sex female couples. Some also consorted with males and thus fledged chicks. This sparked nationwide media coverage, many letters to the scientists, a new song, and such outrage among human politicians that one mention of said research held up the National Science Foundation’s 1978 budget for more than a week.

We now know it’s not just western gulls being gay. It’s everybody — gulls, kittiwakes, terns, shearwaters, albatrosses, penguins, dozens of other birds — and other living things across the animal kingdom: spiders, shellfish, houseflies, turtles, squid, domestic sheep (which can be really annoying if you’re trying to breed sheep), bears — I could go on. And on. To many of the bright-eyed little creatures we feel fellowship for — matrilocal, polyamorous, variable — nuclear families would be odd.

It’s hard to study some of this, naturally. Think of swifts, who can easily spend most of their lives in the air, not bothering to land except to sleep! How do you study their family structures in depth? Or think of albatross, who spend their first several years at sea, barely touching down, and only return to land to breed; how would we know if some of them decided to stay on the open ocean, munching fish, and avoid having chicks altogether? Sounds like a good life to me.