The wild turkeys continue to expand their presence in the Berkeley hills. Some of their new neighbors have mixed feelings about these large untidy and sometimes aggressive birds. And the turkeys may be impacting other species, either through predation (on salamanders and the like) or displacement.
On the other hand, they are without question interesting creatures, with surprisingly complex behavior patterns. UC-Berkeley graduate student Alan Krakauer has shown just how complex in his recent article, “Kin selection and cooperative courtship in wild turkeys,” in the prestigious journal Nature. Krakauer did his field work at UC’s Hastings Reservation in Carmel Valley, but his observations may apply species-wide; he says similar behavior has been documented throughout California and on the east coast.
Almost 40 years ago, a Utah State University doctoral candidate named C. Robert Watts went to the Welder Wildlife Refuge in south Texas to study the local population of turkeys. What he found, as reported in a 1971 piece for Scientific American, was a rigidly hierarchical society. Social rank, Watts claimed, was everything to a wild turkey. A bird’s status was set for life during its first year. He described groups of males, which he believed to be siblings, displaying to females together—a behavior called lekking, also found among prairie grouse, birds of paradise, sandpipers, and other groups of birds. Most of the time, only the dominant male in the dominant group got to mate. His coalition partners displayed for all they were worth, but never got any action.
If evolutionary fitness is all about passing on as many copies of your genes as possible, the behavior of a subordinate male turkey doesn’t make a lot of sense at first glance. Remember that the turkeys are presumed to be brothers, though, with each individual sharing half his genes with his siblings. If only the top-ranking bird mates, he still acts as his brothers’ representative. By helping him attract females and face down rival males, they ensure the perpetuation of those shared genes.
This is the essence of British geneticist W. D. Hamilton’s concept of “kin selection,” widely invoked to explain altruistic behavior in animals—like the self-sacrifice of the worker honeybee—and, by some, in humans. Another Briton, J. B. S. Haldane (or, by some accounts, R. A. Fisher), once did a back-of-the-envelope calculation in a pub and announced: “I will lay down my life for two brothers or eight cousins.”
Watts’s turkeys looked like a classic case of kin selection in action. His study was cited by E. O. Wilson in his magisterial Sociobiology, and referenced in textbooks. There was one problem, though: Watts had never established that the display partners were brothers. Critics argued that since hen turkeys pooled their broods after hatching, young male turkeys grew up in the company of non-siblings and might join display groups with them. And later researchers at the Welder Refuge were unable to corroborate Watts’s observations, possibly because the turkey population had crashed.
Alan Krakauer says he took on the turkey project at the urging of his advisor, Walt Koenig, whose own work at Hastings involves the social life of acorn woodpeckers. “With the complex social system and the mystery about why they’re cooperating, I got hooked,” Krakauer says. Having verified that the Hastings turkeys displayed in groups, he set out to measure the relatedness of the display partners and their contribution to the next generation of hatchlings. That required trapping the wary birds to take blood samples, using a contraption resembling a giant lobster pot baited with cracked corn. “They never really got used to my presence,” he recalls. “They became harder to trap over time.”
Using genetic tools not available to Watts in the ‘60s, Krakauer found that the display partners were indeed bands of brothers. The bond is life-long; coalitions change only when a member dies, and subordinates never strike out on their own. Beyond confirming that only the dominant bird got to mate, his observations showed that dominant males in a coalition mated with more females than solitary males did, and paternity tests established that dominants fathered more offspring than solitaries. Score one for kin selection.
Biologists have documented kin associations among other lekking birds, but none has a system quite like the wild turkey’s. “In black grouse, peafowl, and some manakins, related males display together but each has his own territory,” Krakauer explains. Manakins are small, brightly colored birds of the New World tropics whose courtship routines include an avian version of the moonwalk. Males of some manakin species pool their talents to singe and dance in tandem. “The long-tailed and lance-tailed manakins have a partnership like the turkeys, but the males aren’t related,” he says. “The subordinates don’t get matings, but they may inherit the dance perch or get the opportunity to practice their dances.”
The nearest analog to the turkey brotherhoods may occur in mammals like the African lion and bottle-nosed dolphin. Sibling lions band together to take over prides of females. However, the dominant lion doesn’t monopolize mating opportunities. “Some populations of bottle-nosed dolphins have teams of related males that pester females until they’re ready to mate,” Krakauer says. “It’s not clear whether the males are sharing.”
“We wouldn’t have known about the turkeys without being able to look at their DNA,” he concludes. “It’s a real boon to behavioral ecology.” Finally, the textbook case is bolstered by hard genetic data.
Krakauer’s next project, after finishing his thesis, will involve another lek-displaying bird, the greater sage-grouse. He’ll be working with UC-Davis’s Gail Patricelli, inventor of the robogrouse—a radio-controlled dummy female sagehen that she sends out onto the lek to interact with the males. Patricelli has previously used this technique with satin bowerbirds in Australia. The robotic turkey is still some distance in the future.