Birds Of A Feather: Cooperation, Family Living Common Among Avians

As every parent knows, finding someone to help wrangle the kids on occasion is essential. Apparently the same holds true for birds.

An international study published Wednesday in PLOS Biology finds many birds will forgo reproduction to help other birds care and protect their young. The behavior is called cooperative breeding and is concentrated in geographic hot spots. The study upends the theory cooperation evolved as a result of species attempting to colonize harsher living environments.

"Some people have concluded that environmental variability promotes cooperative breeding and other people have concluded that cooperative breeders tend to occur primarily in environments that are more stable," Carlos Botero, a biologist at Washington University in St. Louis, told Science magazine.

"This difference of opinion is difficult to reconcile, because people have come to opposite conclusions based on very similar metrics of environmental variation."

The results corroborate a Swedish study published earlier this year that involved evolutionary scientists at Oxford and Columbia universities who studied 5,000 species. That study found cooperative breeding must be established before a species attempts to colonize a harsh environment.

Botero was part of an international collaboration led by Michael Greisser of the University of Zurich in Switzerland that examined 3,005 bird species. The study found birds form family groups and resolve their roles before breeding begins. Scientists hope this cooperative behavior will keep some threatened species from extinction.

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Earlier studies pointed to environmental conditions as the reason the cooperative behavior develops. But if the environment is conducive to survival, it often becomes overpopulated, prompting younger birds to become helpers because they are unable to establish a claim to territory themselves. However, the behavior also has been exhibited in areas where the climate is harsh, enabling birds to breed in years where food is limited.

“Family living acted as an essential stepping stone in the evolution of cooperative breeding in the vast majority of species,” the study said.

“First, family living enables coping with variable environmental conditions and increases offspring survival both within and outside the breeding season. Subsequently, it sets the scene for the secondary evolution of cooperative breeding when environments have become more variable throughout the year and during the breeding season.

“Second, we found that cooperative breeding among unrelated individuals is exceptional and likely has different evolutionary origins than family-based cooperative breeding.”

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Cooperative breeding is especially prevalent in southern Africa, Australia and northern South America – all areas where climate change has been dramatic over millennia.

The latest study found there are two transitional steps in going from breeding pairs to cooperative breeding and family groups.

"The bottom line is that oftentimes more productive environments — good environments — favor the evolution of family living, and that once birds are living in groups, exposure to environmental variability may promote the evolution of helping at the nest," Botero said.

Birds are not the only species that employs cooperative breeding. The behavior also is exhibited by anthropods, fish and mammals.

A study published last year in the Auk: Ornithological Advances found young male pheasants in Hawaii willing to care for chicks and defend against intruders rather than strike out on their own, waiting instead to move up in the hierarchy of the family to pass on their own genes.