Even tropical birds will have a hard time dealing with climate change, new study says

A group of researchers from the University of Windsor and University of Guelph have made a surprising discovery about the lifespan of tropical birds in hot climates.

Researchers made 15 annual trips to a conservation area in Costa Rica

University of Windsor professor Dan Mennill examines a rufous-and-white wren. The bird has been the focus of a 15-year study on how their lifespan is influenced by climate. (Dale Morris)

A new study says hot climate conditions actually reduces the survival rate of tropical birds.

The findings, released Wednesday, are the first to examine the influence of climate on the lifespan of male and female rufous-and-white wrens.

Dan Mennill, professor in the Department of Biological Sciences at the University of Windsor, and a team of scientists and students have been spending the past 15 years making annual visits to the Guanacaste Conservation Area in Costa Rica.

The research team 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 Costa Rica experiences warmer and drier temperatures, wrens are more likely to die," Mennill said.

Rufous-and-white wrens inhabit tropical forests along the Pacific coast of southern Mexico to Panama as well as parts of northern Colombia and Venezuela. (Dale Morris)

The findings reveal that animals who are are adapted to live in warm, dry, tropic-like environments are still affected by the surrounding climate.

"You would think if they adapted to a warmer climate, then global climate change isn't going to influence them. That turns out to be false," he explained.

Unknown cause

Over the 15-year period, Mennill observed decreased rainfall and significant warming in the Costa Rica region. This resulted in a 'mass die-off' a few years ago in which the population of the wrens dropped 75 per cent. 

"It's very rare that we find a dead wren on the ground that we could put a chalk outline around and get to the biological mystery of figuring out why," he said.

Dan Mennill discusses his 15-year study which shows hot climate conditions reduce the survival rate of tropical birds. (Video by Lincoln Savi) 0:31

"Instead, what usually happens is we'll have a bird that we've tracked for a year or two or even up to eight years. And then one year we show up and that animal is absent."

Dan Mennill surveys birds with his wife, research partner and University of Windsor biology professor Stéphanie Doucet. (Dale Morris)

What this tells us

The wrens live their entire lives in Central America, but that doesn't mean the findings have no bearing here at home. Menill said Canadians now have a better insight into how animals are responding to climate change.

"The earth's biodiversity is concentrated in a region many thousands of kilometeres away from us here," he said.

"If we can understand how birds locally and distantly are influenced by warming temperatures and decreased rainfall, we will be able to develop a deeper appreciation of how earth's biodiversity will respond to a changing climate."

The study, published Wednesday in Proceedings of the Royal Society of London B: Biological Sciences, found male birds have a heightened sensitivity to climate change. (Dale Morris)

Increased mortality in male birds

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 three metres of rain falls.

University of Guelph professor Brad Woodworth, the study's lead author, said the lifespan of tropical birds is particularly pronounced for males during the dry season.

"Females showed lower survival than males overall, but female survival was not heavily influenced by temperature variation the way it was for males."

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