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Bird populations in the tropics have dropped by roughly a third (25–38%) since 1980 due to intensifying heat extremes, compared to a world without climate change, with some species having declined in abundance by over 50%, according to a study today in Nature Ecology & Evolution with contributions from the Potsdam Institute for Climate Impact Research (PIK), the University of Queensland and Barcelona Supercomputing Center (BSC).

"It's a staggering decrease. Birds are particularly sensitive to dehydration and heat stress. Extreme heat drives excess mortality, reduced fertility, changing breeding behaviors and reduced offspring survival," commented lead author Maximilian Kotz, a guest researcher at PIK and researcher at BSC.

According to the study, tropical birds are exposed to ten times the extreme heat conditions today than they were forty years ago: from an average of three days a year of extreme heat, to thirty days.

The study combines observed data with models to identify the effects of climate change on bird populations around the world—with a focus on heat and precipitation. The biggest drops in numbers were in the tropics, but nearly every region reported a loss of population abundance, with extreme heat having the greatest impact on population declines.

"Rising temperatures are really pushing species out of the ranges that they've naturally adapted to—and in a very short amount of time," Kotz added.

Climate change a rising threat to biodiversity

To date, it's been challenging to distinguish climate change's impact on biodiversity from the losses due to more direct human pressures such as deforestation. The research team's methods were able to do so and indicated that in lower-latitude tropical regions, intensifying heat extremes are already having a bigger impact on bird population loss than deforestation and habitat destruction.

This potentially helps to explain recent findings from undisturbed tropical rainforests in the and in Panama, where large declines in birds were observed without a clear cause.

"On the conservation side, this work tells us that in addition to protected areas and stopping deforestation, we urgently need to look into strategies for species who are more vulnerable to heat extremes to maximize their adaptation potential. That might mean ex-situ conservation work—so working with some populations in other locations," said co-author Tatsuya Amano from the University of Queensland.

"Ultimately, our emissions are at the heart of this issue. We need to be bringing them down as fast as possible," concluded Kotz.