Climate Change Threatens Tropical Birds with Extreme Heat Waves

From the dense tropical forests of Central and South America to the open savannas of northern Australia, equatorial climate zones harbor a rich diversity of birds, including macaws, toucans, and hummingbirds that thrive in warm, humid environments.

However, as the pace of climate change accelerates, the tropics are facing a significant increase in the number of days with extremely high temperatures – on average ten times faster than four decades ago. Such extreme heat events threaten the survival of even the world’s most popular birds, according to recent research.

According to data published in Nature Ecology & Evolution, from 1950 to 2020 extreme heat events reduced tropical bird populations by roughly 25–38%.

It clearly points to the need to tackle greenhouse gas emissions, because these heatwave scenarios will rise over time.

Key findings and methods of the study

Scientists gathered more than 90,000 scientific observations from over 3,000 bird populations and compared them with daily weather data that have been kept since 1940 to understand how species respond to extreme temperatures and other climatic phenomena.

Data on anthropogenic impact were also compared to isolate the influence of climate change against other factors driving habitat destruction.

Exposure to thermal extremes (temperatures exceeding the 99th percentile) led to population declines at latitudes below 55° N or S, with the strongest impact recorded in the tropics – in regions below 23° latitude.

The authors emphasize that the rising frequency of heat waves has a greater impact on birds than the annual average temperature rise associated with climate change.

Impact on the tropics and biodiversity

It is not surprising that bird populations are declining: previous studies in the United States and Canada indicate a decline of about 30% since 1970, meaning the loss of about 3 billion birds.

A substantial portion of these losses is linked to direct human impact – habitat loss due to agriculture, logging, mineral extraction, or collisions with buildings and infrastructure.

The study highlights the threat of heat waves to tropical birds and explains why even in remote and protected areas they face difficulties in surviving and reproducing.

In two pristine tropical forests in Panama and the Amazon, bird populations declined by more than 50% for most species between 1977 and 2020, and also between 2003 and 2022.

When birds are subjected to extreme heat, they become hyperthermic: their body temperature rises to dangerous levels. Since birds do not sweat, they must breathe more rapidly or expose their skin to cool down. This leads to dehydration, exhaustion, disorientation, and sometimes loss of consciousness, which can cause them to leave the nest. Excessive heat also damages organs and lowers birds’ reproductive capabilities.

Why are the tropics so important for biodiversity while at the same time making them especially vulnerable to climate change? They host many rare and small populations of species that are sensitive to temperature deviations, creating a narrow thermal niche in which they survive. Climate change forces these birds to seek new habitats and retreat beyond their usual ranges.

This is almost a perfect storm

In the tropics there are species with very small populations that have occupied a narrow temperature niche, making them especially vulnerable to temperature fluctuations and environmental changes. Such conditions heighten their sensitivity to winter seasonal fluctuations and to climate shifts in general. According to Maurer, these circumstances contribute to the tropical world’s extraordinary biodiversity, but rising heat forces birds to move beyond their usual comfort zones.

When temperatures exceed the bounds of these comfort zones, birds face adaptation challenges. And as Watson notes, populations are smaller and have limited evolutionary capacity compared with other regions, increasing the threat to species’ survival.

We cannot simply sit back and hope that species will be safe because they live in protected areas. Climate change is so pervasive that it will touch even these territories.

Maurer emphasizes that this study should serve as another warning signal: greenhouse gas emissions and climate change pose a serious threat to biodiversity. In his words, reducing the impact of climate change must become a top-priority strategy, because without it many tropical species risk extinction.

We must reduce climate change as a top-priority strategy, or else we will lose a huge number of tropical species if we do not do this.