A study published in Nature reported steep declines in tropical bird populations since 1950, including about a 40% decline in species and a 25–38% drop in overall populations since 1980. The research team analyzed population changes for 3,000 bird species from 1950 to 2020, using statistical models to assess the role of extreme heat, reported ABC News Australia.
The researchers combined observations and climate models to separate the effects of heat and precipitation from other pressures such as habitat loss, focusing on how populations changed after abnormal weather. Their models indicated that intensified heat extremes mattered more than average temperature or precipitation shifts. These effects held when controlling for changes in industrial pressure and other long-term drivers.
Exposure to extreme heat drove large declines worldwide, especially in tropical regions where many birds already lived near dangerous temperature thresholds. Tropical birds now faced roughly 30 days of heat extremes per year, up from about three in the mid-20th century; at higher latitudes the increase was smaller, from about three to ten days.
In lower-latitude tropical regions, intensifying heat extremes already had a greater impact on population loss than deforestation and habitat destruction, challenging the view that direct human pressures dominated in the tropics. In sub-tropical regions, climate impacts were typically smaller than direct human pressures; in mid-latitudes between 21° and 43° north or south, habitat destruction remained the main driver of declines.
Large losses also appeared in areas with little direct human presence. In parts of the Amazon and Panama, some populations fell by as much as 90 percent. Studies in well-protected forests in Panama and the Ecuadorian and Brazilian Amazon reported losses of up to 50 percent over about two decades. The team did not find evidence of recovery until five years after initial heat impacts, suggesting effects accumulated over time.
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, said Maximilian Kotz of the Barcelona Supercomputing Center and the Potsdam Institute for Climate Impact Research. Rising temperatures were pushing species out of the ranges they had adapted to in a short time, said Kotz. Without addressing climate change, that would not be enough for the birds. Ultimately, our emissions were at the heart of this issue. We needed to bring them down as fast as possible, said Kotz.
The study used climate-impacts attribution methods to estimate how much the intensification of heat extremes came from human-caused warming, applying this approach to ecological outcomes. The data suggested tropical birds often faced conditions beyond their physiological limits. Even when adults survived heat events, poorer body condition reduced breeding success. Extreme heat lowered body condition, limited foraging, stressed eggs and chicks, and led to dehydration or nest abandonment. Hummingbirds increasingly sought shade, reducing time for nectar foraging. The research found that extreme events reduced breeding rates and altered breeding timing, raising mortality among young and adults.
Nearly half of all bird species lived in tropical regions, making these declines a major risk for global biodiversity. Many of these areas also saw more frequent and severe heatwaves and dry spells, as well as increased fire activity. Impacts were strong for groups such as songbirds and birds of prey; some aquatic-associated groups showed different responses, likely tied to access to water.
On conservation, we urgently needed to look into strategies for species 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 Tatsuya Amano of the University of Queensland.
In northern Australia’s dry tropical savannas, birds faced added risk from volatile water sources. Birds can’t sweat, so they’re struggling to shed heat. They pant, but that contributes to water loss, said Golo Maurer of BirdLife Australia. They started at a higher body temperature than humans, which allowed them to live in warmer climates, but beyond about 42 °C they struggled, said Maurer. The endangered Carpentaria grasswren began venturing out during the hottest part of the day to find water, raising the risk of overheating.
We needed long-term datasets like the authors used to understand how extreme temperatures affected avian populations, said Aimee Van Tatenhove of Cornell University’s Center for Avian Population Studies.
Although land clearing, hunting, and habitat degradation reduced global bird abundance by roughly 10–20 percent, the study found climate change—particularly intensifying heat extremes—was the main driver of tropical declines. The authors wrote that there was an urgent need to test conservation strategies that could help tropical species persist during heat peaks, alongside efforts to cut fossil-fuel emissions.
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