For the Birds Radio Program: Cooperation: An Overview (Part 1)
Human and bird societies are quite different in many ways. A lot of this is due to how long it takes to raise human children to become independent. The most fertile women on earth may produce a baby every year for eight or ten or even 20 years, but most of us produce children during a much shorter span. Either way, a new baby is dependent on us or another caretaker 24-7 for several years, and after that only slowly grows independent. It’s hard work to take care of a child plus have the resources to provide for its needs, so we depend on extended family, paid babysitters and daycare, and schools to share some of the responsibilities. And we also rely on the criminal justice system and military to assume some of the responsibilities of defending our own personal territories against criminals and foreign invaders.
Like us, birds do come together in times of trouble—if a large owl shows up, crows will assemble from miles around to drive it away. But as far as petty theft of food resources on a territory, birds are entirely on their own, and when an accipiter or falcon rips through, it’s every bird for himself.
Most bird pairs, and some individual bird parents, go it entirely alone while raising their young. A robin pair manages to raise four babies from newly-laid eggs to independent birds in about 6 weeks, and can produce three or sometimes even four batches of these young in a single summer. Then, of course, these exhausted robin parents take the fall and winter off, with no parental responsibilities at all.
Hummingbird males find, advertise, and defend territories onto which they attract females. After the act of mating, the males are done—they may not even recognize their own young—but the females raise two young entirely on their own, and often renest once or twice in a summer. In many shorebirds, it’s the female who is territorial and the male who raises the young. In both cases, the young are fully independent within weeks or at most a couple of months.
Swan, goose, and crane parents stay with their young during the first migration and throughout the first winter. In geese and swans, the babies learn their migration route and where to find the best feeding areas from their parents, but parental responsibilities are pretty simple—the young are so eager to learn and so eager to do everything exactly the way that their parents do that really, the parents go about their daily business with no more stresses than they would without their young. Whooping Cranes switch their diet to blue crabs in winter, and the parents do spend time patiently teaching their young how to find and open them, but at least in years when blue crabs are abundant, this doesn’t represent a hardship.
Some young birds take a couple of years or more to mature enough to be able to establish a territory of their own and raise their own young. Meanwhile, they may wander about as what are called floaters, without a territory of their own, trying to elude territorial pairs including their own parents. But in a few species, these young birds are welcome to remain on their parents’ territory, using additional resources but also helping their parents raise the next year’s young. This is one form of cooperative breeding. Cooperative breeding comes in many forms, and is employed by many unrelated species, including Australian fairywrens, many species of starlings, American Crows, Florida Scrub-Jays, Groove-billed Anis, Western Bluebirds, and Acorn Woodpeckers. This week we’ll focus on some of the birds that cooperatively breed, and on some of the scientific research that is delving into the evolution of this fascinatingly family-friendly lifestyle.