Tropical bird populations are facing a severe crisis as extreme heat events, intensified by climate change, drive dramatic declines in their numbers. A new study published on August 11 in Nature Ecology & Evolution quantifies this impact, showing that tropical land bird abundance has dropped by 25% to 38% from 1950 to 2020—a loss primarily linked to escalating heat extremes.
Led by Maximilian Kotz of the Barcelona Supercomputing Centre, the research team analyzed data from the Living Planet Database, which tracks global terrestrial bird populations, alongside historical climate records from the European Centre for Medium-Range Weather Forecasts and habitat destruction metrics. Their findings reveal a striking contrast between regions: in mid-latitudes (21° to 43° North/South), habitat loss remains the key driver of bird decline, aligning with previous studies. However, in tropical zones, extreme heat dominates as the most significant threat.
Tropical birds are particularly vulnerable because they live near their physiological heat tolerance limits. Beyond surviving direct heat stress, elevated temperatures impair their health, reducing breeding success and long-term survival. “These birds are already operating on the edge,” explains Kotz. “Even small increases in extreme heat can push them past a critical threshold.”
The study’s climate attribution framework—used here for the first time in an ecological context—compares observed bird populations with a counterfactual scenario without human-driven warming. This analysis confirms that human activities are directly responsible for the intensified heat extremes behind the declines. Notably, the impacts are evident even in nearly undisturbed habitats like the Amazon and Panama rainforests, where some bird species have declined by up to 90%.
While data gaps exist, especially in tropical regions, Kotz notes that this likely underestimates the problem. “The missing data in these areas would probably reveal even more severe impacts,” he says.
Though the study does not project future trends, the implications are troubling. As global warming accelerates, extreme heat events are expected to become more frequent and intense, threatening further losses. “The situation is grim,” Kotz emphasizes, underscoring the urgent need for climate action to protect tropical biodiversity.
The research not only highlights the unique vulnerability of tropical ecosystems to climate change but also introduces a new method for quantifying ecological impacts of global warming—offering a critical tool for understanding and addressing biodiversity loss in a changing world.