Record Heatwaves Threaten Tropical Bird Populations by 25-38% due to Climate Change: Study

In equatorial regions spanning the rainforests of Central and South America, the savannas of northern Australia, and beyond, an array of vibrant avian species flourish, from macaws to toucans to hummingbirds, thriving in hot and humid environments. However, a study published in Nature Ecology and Evolution warns that climate change is driving a surge in dangerously hot days, potentially threatening the existence of these colorful birds.

From 1950 to 2020, extreme heat events reduced tropical bird populations by 25% to 38%. The research indicates that such heat events are a primary cause of species loss, as even pristine habitats worldwide have witnessed declining bird populations.

James Watson, a professor in conservation science at the University of Queensland and one of the study’s authors, explains that these extreme heat scenarios are set to increase over time, urging the need to address greenhouse gas emissions. Watson and his colleagues analyzed over 90,000 scientific bird observations from more than 3,000 populations, matched with daily weather records dating back to 1940, to understand how birds respond to extreme weather events such as heatwaves and heavy rainfall.

The findings reveal that exposure to heat extremes (temperatures surpassing the 99th percentile) led to a decrease in bird populations below latitudes of 55 degrees north or south, with the most significant effects occurring in tropical regions (below 23 degrees). The researchers discovered that the impact of heat extremes outweighed annual average temperature increases caused by climate change.

While the notion of bird population declines is not novel – a 2019 study reported a 30% drop in US and Canadian bird populations since 1970, amounting to nearly 3 billion birds – much of this loss has been attributed to direct human impacts like habitat destruction due to farming, logging, mining, or building collisions.

This latest study highlights the danger posed by extreme heat to tropical bird species, explaining why bird deaths are occurring even in remote and protected areas often regarded as havens of biodiversity. Between 1977 and 2020, bird populations declined by more than 50% for most species in two undisturbed rainforests: one in Panama and the other in the Amazon.

When birds are subjected to extreme heat, they may develop hyperthermia – a condition where their body temperature rises dangerously high. Since birds cannot sweat, they respond by panting or exposing more skin to release heat. This can lead to dehydration, disorientation, loss of consciousness, and even falling from perches. Extreme heat can also cause organ damage in birds and impair their reproductive capacity.

The tropics, teeming with unique species, are particularly vulnerable to climate change due to their small population sizes and limited evolutionary adaptability. Golo Maurer, the director of bird conservation strategy at Birdlife Australia, likens it to “almost a perfect storm.” In tropical areas, species have adapted to thrive within narrow temperature ranges, creating biodiversity hotspots. However, when temperatures exceed these comfort zones, tropical birds struggle to adapt, according to Watson.

Maurer emphasizes that the study underlines the importance of recognizing that climate change will affect even protected areas and that species cannot be considered safe simply because they reside in protected habitats. Maurer has observed the impact of climate change on birds in his tropical home of north Queensland, Australia – an area renowned for its biodiversity with a significant number of endemic birds.

For instance, volunteers from BirdLife have been compelled to venture to higher elevations to spot golden bowerbirds, small yellow birds with a limited range that inhabit the rainforest in Queensland. Watson stresses that the study serves as “another wake-up call that greenhouse gas emissions and climate change pose a significant threat to biodiversity.”

“We need to reduce greenhouse gas emissions as a primary strategy,” Watson concludes, “because we risk losing vast numbers of species in the tropics if we don’t.”