"Since rain equals food to the birds because it drives patterns of insect availability," said Rubenstein, "we think that by living in family groups with helpers that aid in feeding babies, these birds can cope better in these unpredictable savannas."
Rubenstein noted that this social strategy also helps in good years with lots of rain. Helpers bring enough extra food back to the nest to allow the cooperatively breeding species to breed longer and raise more broods of young than the non-cooperative ones.
"In some cases, the more social species tend to breed longer in benign years and thus produce more offspring," he said. "Often, parents don't have to spend so much time and energy going out and getting food because helpers compensate and do a lot of the parenting."
The origin of cooperative breeding in a savanna habitat may extend beyond starlings, Rubenstein said, noting that the first humans also lived in the savannas of East Africa.
"We think this relationship between sociality and temporal variability in rainfall and, hence, food availability, might help explain the distribution of cooperative breeding in other groups of birds, and even some mammals, living in semi-arid environments around the world," he said.
He added that with global warming, weather patterns are expected to become more variable worldwide and could possibly drive social behavior more toward cooperative breeding among temperate species that don't normally live in family groups.
|Contact: Robert Sanders|
University of California - Berkeley