Uncertainty drives the evolution of 'cooperative breeding...( Rather than striking out to start a ...)

Rather than striking out to start a family of their own, members of some bird species will stick around longer to help a relative raise their young. Now, researchers report evidence that in African starlings such altruistic tendencies are most common among species that live in savannas, where the rainfall in any given year is virtually impossible to predict. The findings appear online August 16 in the journal Current Biology, a publication of Cell Press.

When the unpredictability of your environment is high, you dont know in advance what conditions you will be facing when the next breeding season rolls around, said Dustin Rubenstein of the University of California, Berkeley and the Cornell Laboratory of Ornithology. Faced with this uncertainty, it pays, evolutionarily speaking, to live and breed in social groups that will help you weather the bad times and make the most of the good times. Living in cooperative family groups may be like a form of insurance against the unpredictable nature of the environment that allows individuals to maximize their reproductive success over the course of their lifetimes.

Over the past few decades, mounting evidence has shown that many species of cooperatively breeding birds live in semi-arid tropical and sub-tropical environments, particularly in sub-Saharan Africa and Australia. Although that pattern suggested that the environment might explain the behavior, few studies showed a strong relationship between the incidence of cooperative breeding among species and any particular environmental feature, the researchers noted.

In the new study, the researchers examined the pattern of breeding behavior exhibited by 45 species of African starlings in relation to the environments in which they liveincluding savannas, deserts and tropical forestswhile controlling for the evolutionary relationships among them. They also examined the rainfall patterns typical of each of those environments in 47 African countries
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