Bluebirds Benefit From Living At Home For a Year Before Moving Out, Study Shows

Seeing as female western bluebirds prefer mating with older males, a new study from Cornell University and the Santa Fe Institute suggests it is advantageous for young bachelors to live with their parents as a helper for a year before starting a nest of their own. 

In addition to this age bias, bluebirds have high rates of extra-pair paternity (EEP), which means that a female's social mate may not be the father of all her offspring. Therefore, if males mate at a younger age they may decrease the genetic diversity of their offspring. 

Furthermore, researchers suggest helping behavior often benefits longevity, whereas by sharing the workload, each individual in a cooperative nest has a survival advantage. For long-lived species like bluebirds, which live for an average of eight years, delayed cooperative breeding may also increase reproductive fitness, or the likelihood of passing their genes onto the next generation. 

"It's a unique and somewhat counterintuitive interplay of evolutionary tradeoffs that makes this kind of cooperative breeding advantageous for species like bluebirds," Caitlin Stern, lead author of the study and an Omidyar Fellow at the Santa Fe Institute, said in a news release. 

Interestingly, cooperative behavior is generally seen in monogamous populations with low EPP. 

"If you have this combination of an age bias -- such that young males are not likely to sire offspring in another male's nest but old males are -- and if helpers and their parents have a survival advantage, you can get this evolution of helping behavior even in systems with high rates of EPP," Stern explained. 

Researchers suggest their study emphasizes the importance of considering a species' full life history when studying behaviors. 

"Our study is a case-in-point for the need to do this," Stern concluded. "An individual's fitness accumulates over its lifespan, and we need to take that into account when we're looking at the evolution of behavior."

Their study was recently published in the journal Behavioral Ecology. 

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