From 'duds' to 'studs'—even cowbirds need mentors to learn lessons of love

By Jayne Spencer

From our archives: Feb. 5, 1996

Pity the poor male cowbird. Hatched as he is in the nest of strangers, who will teach him the signature songs that define him? Do cowbirds get the blues?

"Many songbirds use songs to attract mates and thus a male with a poor song may not attract a mate and may not pass on its genes," explained IU animal behaviorist Meredith West, who along with colleagues Andrew King and Todd Freeberg, has been studying the vocal repertoires and courtship skills of young male cowbirds.

In a research article published in the Journal of Comparative Psychology, the three explore the unique place of the cowbird in birdsong studies. In the past quarter century, scientists have explored parallels between birdsong and complex human learning such as human speech.

"Language is learned, yet the 'instinct' to learn it suggests biologically or genetically controlled pathways bred into the brain to anticipate deficiencies in a young learner's environment," said West. "Even in cultures where parents deliver monologues to their newborns, the caretakers could not possibly provide all the material needed to extract the rules of language."

Since cowbirds are "brood parasites," the artful cowbird parents deposit the eggs of their offspring in the purloined nest of one of more than 200 different species or subspecies of birds, allowing the nestholders the unwitting privilege of raising the young interlopers as their own.

Scientists studying songbirds' behavior and their brains have found compelling evidence that each songbird's signature— its songs—is the product of guided learning; birds not only need to hear sounds, but require exposure and experience with the older generation in how, when, where and what to sing.

If the young male cowbird is raised without hearing adult male cowbirds sing, will his genetic programming—his "genetic safety net"—be sufficient to ensure that he develops a song and uses it to attract a mate?

"How cowbirds find other cowbirds has always been a question," said West. "And most people have assumed that the answer was genetic programs, essentially genes for 'recognizing' another cowbird. We found it is not that simple."

On the 93-acre field station that serves as one of the living laboratories for IU's Research Training Group, an integrative graduate program that pools the expertise of psychologists, biologists and neuroscientists studying animal behavior, the researchers housed one group of young male cowbirds from the Black Hills of South Dakota with female cowbirds. The second group of male cowbirds were housed with canaries.

Why canaries?

"We reasoned that canaries could not teach cowbirds anything about how to sing like a cowbird and would allow us to see how far the young males could get in learning to sing based only on their presumed genetic safety net," said West.

Following eight months of this living arrangement, the songs of the young male cowbirds were recorded before they were put into two new living environments.

First they were placed in large flight cages and then in large aviaries. In each case, the male cowbirds were meeting with unfamiliar cowbird females and a mix of unfamiliar canaries to see what they would do when given a chance to court.

The results erased any idea of a genetic safety net the scientists might have had.

The male cowbirds who had lived with canaries went gaa-gaa over the new canaries, at times seeming almost oblivious to the female cowbirds in their midst. The young males would fly or hop over a female cowbird in pursuit of this other species.

The young males' behavior did not change even after witnessing the successful courtship of female cowbirds by more experienced male cowbirds.

"To put it simply, the young males who had lived with canaries showed little signs of

species identification. We think the female cowbirds were as surprised as we were," said West.

Perhaps, the researchers speculated, the young males had become "imprinted," like chicks or ducks or swans (remember "the ugly duckling?") on the "wrong" species.

But that theory didn't fly.

If imprinting were at work, the male cowbirds originally housed with female cowbirds should show strong bonds with the female cowbirds. And while the young males showed an affinity for their female counterparts and ignored the canaries when housed in cages, in the aviaries, where the community included more mature, normally reared adult male cowbirds, a completely different dynamic transpired.

The young males "hung out" together and sang to each other. All courtship shut down.

"These males had the same genetic programming as the males that were chasing canaries, so why weren't they chasing female cowbirds?" asked West. "The explanation we arrived at concerned what we perceived, and then measured, as social pressure from other males of their own age and from older, normally reared male cowbirds."

The songs of the young male cowbirds who had lived with female cowbirds were more "cowbird-like," not "canarized" as the songs of the males that had lived with canaries. The male cowbirds' proclivity for "hanging out with the boys" had been a result, West believes, of the female-housed males' inability to learn to do two things at once: to sing to other males in contests—something routinely observed in cowbirds living in their natural environment—and to sing to females as part of the courting process.

As all young male cowbirds in the wild know, to impress a female cowbird, the male must follow from a polite distance and stop when she stops. Some of the young males in captivity chased the females but just kept on going when the female perched, running a race rather than winning a sweetheart.

After a few weeks, the researchers decided that the young males needed role models; if they saw adult male cowbirds "in action" with the female cowbirds, maybe they'd get the idea. And that's when the researchers found that with the addition of the older males, not even the boldest among the young cowbirds spent time near the female cowbirds.

"It was hard to resist seeing the young males like teenagers at a dance," said West. "When only other freshman males are there, the boys socialize and flirt a bit with the girls

but when the senior 'men' arrive, the younger boys are back in the corner of the gym talking 'guy talk.'" Following the breeding season, some of the young males faced a lengthy "rehabilitation;" in the second year, they were housed with both female cowbirds and older male cowbirds.

The experiment was a success.

"The males allowed to interact with older males switched from novices to experts—or as other have called the transition, from `duds' to 'studs.' So it was clear that even male

cowbirds housed with female cowbirds do not have an adequate genetic safety net to ensure mating success—they had better songs, but they did not know how to use them."

The experiments led the researchers back to what is considered two of the most important components in behavioral science: nature and nurture.

As a result of its parasitic trick of laying eggs in other birds' nests, the cowbird remains "a wild card in the evolutionary scheme," West said. While many biologists have assumed that cowbirds functioned with a "genetically closed" system of behavioral development—a genetic "latching" of the window of experience—the species, in fact, shows a surprising degree of behavioral flexibility.

In matters of courtship and the songs of love, "young males, without experience with older males, just do not get it."

"An ability to notice and to copy and to learn from the consequences of interactions with companions is thus potentially quite adaptive," West said. "Rather than social learning leading to the wrong ends, learning seems to ensure achieving the right ones."

How do cowbirds find each other in nature? For one thing, they share physiological biases for certain foods, grasshoppers, for instance, and thus congregate where the grasshoppers are bountiful. "Like attracts like" in many species: food calls match, plumage is familiar. For the social cowbird, such "coincidences" lead to lots of consequences.

Maybe cowbirds find one another partly because they share the experience of growing up in the nests of strangers, West speculated.

A young sparrow may at some point spurn his cowbird nestmate, a classic case of sibling rivalry caused, perhaps, because the voracious cowbird out begged the rightful nestling. "Without too many more steps, a mixed flock of sparrows and cowbirds might begin to separate by virtue of social and physiological magnets aligning them to different parts of the environment," West said.

Cowbirds or "buffalo birds" as they were called at the time, fascinated the native American tribes, European explorers and pioneers who were struck by the sight of rows of birds sitting together on the spiny ridge-poles of bison grazing on the Plains.

Stories abound of the resourceful birds and their unexpected companions. Often the buffalo bird could be sighted fashioning cushy hollows in the warm wool behind the buffalo's horns. Thus sheltered against the harsh weather and attacks by both animal and human foes, the bird assured for itself one more season in the chorus line.

#

(birdsong)