Climate change and extreme heat play a role in decline of tropical bird population, study finds

Climate change is responsible for a nearly 40 per cent decline in the average abundance of tropical bird species since 1950, a new study has found.

The joint study from the University of Queensland and Barcelona Supercomputing Centre in Spain, published in the journal Nature Ecology & Evolution, found severe weather events had combined to reduce fertility, alter breeding habits, and kill both young and mature birds.

The study used open-source bird data to map the population of 3,000 bird species worldwide between 1950 and 2020.

Using statistical modelling and noting how those bird populations changed after abnormal weather events, the authors were able to specifically assess climate change’s impact on species.

They found a 25-38 per cent decline in the overall abundance of tropical species, largely due to prolonged and extreme heat.

Professor James Watson from the University of Queensland, one of the report’s authors, said while the impact of gradual climate change was well understood, extreme events had been largely ignored.

“This piece of science showed that it’s actually the biggest factor causing declines in tropical birds around the world,” he said.

The paper found tropical species were more sensitive to events like heatwaves, droughts and floods than those that live in milder climates.

Professor Watson said the team had a number of theories as to why.

“If you look broadly at tropical regions, most species have very small ranges. They’re highly specialised,” he said.

“When you go further away from the tropics, a lot of species have much wider ranges … so they’re available to adapt to different kinds of climates.”

Birds ‘struggling to shed heat’

The study found birds that live in dry, tropical savannas, which stretch across much of northern Australia, are at particular risk due to the volatility of water sources.

Through climate change, these areas are seeing increasingly frequent and severe heatwaves and dry spells, as well as increased fire activity, according to the report.

Dr Golo Maurer — the director of Birdlife Australia’s Conservation Strategy, based in Cairns — said birds of all varieties struggled to cool themselves in extreme heat.

“Birds can’t sweat, so they’re struggling to shed heat. They pant, but that contributes to water loss,” Dr Maurer said.

“They start at a higher temperature than we do, which allows them to live in warmer climates.

“But once you push on beyond 42 degrees, they’re really struggling.”

Birdlife Australia coordinates thousands of volunteer citizen scientists, whose work is partly responsible for the datasets that studies like this rely on.

Dr Maurer said teams out in the field were working on Birdlife Australia’s own report into species abundance in Far North Queensland and had noted similar concerning population drops, particularly amongst smaller varieties.

This, he said, is because smaller birds are unable to store energy as effectively, must feed more frequently, and are therefore unable to hide themselves away during extreme heat events.

It means species like the endangered Carpentaria grasswren have changed their behaviour to come out in the middle of a hot summer day in order to find water, putting them at serious risk of overheating.

Dr Maurer said some population declines in wet tropics species are so concerning, Birdlife Australia has recommended some species’ have their threat classification upgraded.

“Certain species now just live in a fairly narrow band along mountain ranges where they are finding the right temperatures.

“The famous golden bowerbird, for instance, the smallest of the bowerbirds … seems to have been abandoned some areas, so they’re not coming down the mountain anymore.”

One of many challenges

The study also found that other human activities, such as land clearing, hunting or the degradation of habitat, had also combined to reduce bird abundance by between 10 to 20 per cent globally.

However, it found some of the places most severely impacted by population declines were outside the physical reach of humans.

“In two relatively undisturbed rainforests in Panama and the Amazon, abundance declined by over 50 per cent for the majority of bird species between 1977 and 2020,” the report said.

In order to give at-risk bird species a fighting chance of surviving already “baked-in” climate change, Professor Watson said it was essential to protect as much habitat as possible.

“The only way these species in the tropics are going to survive these extreme events is if they have healthy populations,” he said.

“Every single bird that we see out there has adapted to natural climate change events in the past, which means they have the internal mechanics to adapt to rapidly changing climates in the future.”