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Dan Mennill holding tropical wrenBiology professor Dan Mennill with a rufous-and-white wren. He led a 15-year study showing that warm temperatures reduce survival of this tropical bird. (Photo by Dale Morris.)

Hot climate reduces survival of tropical birds, study finds

A 15-year study led by University of Windsor researchers shows that a hot climate reduces survival in tropical birds. The new study, which appears today in the journal Proceedings of the Royal Society B: Biological Sciences, asks the question: How do temperatures and rainfall influence survival of male and female tropical songbirds?

“Most of Earth’s birds, and most of Earth’s biodiversity, are concentrated in the tropics,” says Dan Mennill, a professor in the Department of Biological Sciences and the senior author of the study. “But studies of how climate influences animal survival have focused primarily on migratory birds or birds that live in temperate environments.”

The research team, made up of biologists from both University of Windsor and University of Guelph, studied a population of rufous-and-white wrens living in the Guanacaste Conservation Area in Costa Rica. Each year, for a decade-and-a-half, team members captured birds in mist nets, gave each animal a distinctive combination of coloured leg bands, and then surveyed the population to see which birds were still alive and which had perished.

“When we related wren survival to climate, we found that the survival did indeed vary with climate,” says Brad Woodworth from the University of Guelph, co-author of the study. “Most notably, when temperatures were high, the wrens suffered higher mortality.”

The forests of northwestern Costa Rica experience two seasons: a dry season between December and May of each year when rain is absent, and a wet season between May and December when as much as 3.0 meters of rain falls.

“Survival was particularly sensitive to conditions during the dry season, and it was particularly pronounced for males,” says Dr. Woodworth. “Females showed lower survival than males overall, but female survival was not heavily influenced by temperature variation the way it was for males.”

Dr. Mennill calls it an exciting finding.

“It is important to develop a better understanding about how climate influences survival of many different types of animals,” he says. “Our research shows that local climate has a direct effect on survival of tropical birds, and that the effect varies for males and females.”

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