Bird populations in tropical regions have dropped by an estimated 25 to 38 percent since 1980, largely due to increasingly frequent and intense heat extremes linked to climate change.

In some cases, the decline has been even more severe, with certain species seeing their numbers reduced by more than half, according to new research.

The findings, published in the journal Nature, come from scientists at the Potsdam Institute for Climate Impact Research (PIK), the University of Queensland and the Barcelona Supercomputing Centre (BSC).

How is extreme heat affecting tropical birds?

Lead author Maximilian Kotz, a guest researcher at PIK and also at BSC, described the scale of the decline as staggering. He explained that birds are highly vulnerable to dehydration and heat stress, and that extreme temperatures can cause increased mortality, lower fertility, changes in breeding behaviour and reduced survival rates for offspring.

The study found that tropical birds now face extreme heat on about 30 days each year, compared to just three days four decades ago it is 10 times more than in 1980.

Can climate change’s impact be separated from other threats?

By combining observational data with climate models, the researchers were able to pinpoint the effects of climate change on bird populations, focusing particularly on heat and rainfall.

They concluded that without human-driven climate change, tropical bird populations would be 25 to 38 percent higher today. This decline has been building steadily from 1950 to 2020.

While the steepest losses were seen in the tropics, almost every region experienced reductions in abundance, with extreme heat identified as the biggest cause. Kotz pointed out that rising temperatures are pushing species out of their natural habitats within an alarmingly short time.

Is heat now a bigger threat than deforestation?

Previously, it was difficult to separate the effects of climate change from those of direct human activities such as deforestation. The study’s approach made this possible, revealing that in some low-latitude tropical regions, heat extremes are already causing more population loss than habitat destruction.

This finding may help explain sharp declines recently observed in pristine tropical rainforests in the Amazon and Panama, where no clear cause had been found.

What can conservation do to help?

Co-author Tatsuya Amano from the University of Queensland said that while protected areas and stopping deforestation remain crucial, conservation strategies must also address species most at risk from extreme heat. This could mean ex-situ conservation, relocating some populations to other areas to increase their chances of survival.

Kotz stressed that the underlying problem remains greenhouse gas emissions, and that reducing them as quickly as possible is essential to protecting bird populations.