Social pecking order gives roosters something to crow about

In a rooster-peck-rooster world, rank has its privileges. The male at the peak of the pecking order almost always crows first in the morning, researchers say.

After the top bird’s inaugural cock-a-doodle-doo, subordinate roosters then crow, often in order of descending rank, says Tsuyoshi Shimmura of Nagoya University in Japan. Moving the top rooster away from the group inspires the second-ranked rooster to crow first, Shimmura and colleagues report July 23 in Scientific Reports. “The subordinate roosters compromise their circadian clock for social reasons,” Shimmura says.

The study shows just how tied to rank that signaling and other animal behaviors can be in a hierarchical system, says behavioral ecologist Jennifer Foote of Algoma University in Sault Ste. Marie, Canada. She studies dawn choruses, the natural burst of song that erupts from many wild birds at daybreak.

The rooster lab experiment grew out of a chance observation, Shimmura says. He and his colleagues are searching for genes for innate vocalizations, such as “cock-a-doodle-doo,” that an animal develops spontaneously without having to learn how to do them. The project requires listening to a lot of crowing, which revealed the hierarchical sound offs.

Researchers first put four roosters at a time in the same cage in a soundproof room so there would be no interfering cues from outside. The birds then pecked and postured until they had established a hierarchy. For observations of early morning crow-offs, researchers moved each bird into a separate cage in the same room. At the end of the observation period, the rankings stayed the same. The ranking ruled dawn wake-up calls driven by the roosters’ circadian rhythms, but not crowing prompted by sounds or other events.

For behavioral ecologist Bart Kempenaers, caging during the setup phase raises questions about translating results to the wild. Keeping birds so close to each other “might force the subordinates to be ‘very subordinate,’” says Kempenaers, of the Max Planck Institute for Ornithology in Seewiesen, Germany. In a more natural and spacious setting, “the dominance hierarchy might still exist, but the birds can space themselves such that the dominant one is perhaps not the only one that can make noise.”

Dawn choruses in the wild don’t appear entirely random, though what drives their patterns isn’t yet clear. Kempenaers and colleagues reported in 2006 that among the small, active European birds called blue tits, older males start singing earlier than do males in their first breeding season. (Artificial lighting at night, however, prompts earlier song in both young and old.) And a 1997 study from Queens University in Kingston, Canada, found that higher-ranking male chickadees started singing earlier, and sang longer, than did birds at the low end of the pecking order. Just how early and how zestful male singing is, that report said, might help female birds in the audience separate winner males from losers.