Drivers and spatial patterns of avian defaunation in tropical forests

Background

Tropical forests harbor an immense diversity of bird species, but hunting and wildlife trade are driving widespread declines in bird populations. Unlike habitat loss, hunting often occurs in seemingly intact forests, making its impact more difficult to detect. Birds are harvested for both subsistence (food) and commercial purposes (pet trade), but the spatial extent and drivers of avian defaunation remain poorly understood. This study aims to assess the factors influencing bird population declines and map defaunation patterns across tropical forests.

Goals and Methods

The study aimed to identify the key drivers of hunting-induced declines in bird populations, quantify the spatial extent of avian defaunation across tropical forests, and differentiate defaunation patterns between birds harvested for food and those captured for the pet trade. To achieve these objectives, researchers compiled data from 2,968 abundance estimates for 518 bird species across hunted and non-hunted sites in tropical forests. They employed Bayesian modeling to assess how species traits such as body size, human accessibility, and socioeconomic factors influenced hunting pressure. Using species distribution data, they projected defaunation patterns across different tropical regions, providing a clearer picture of where and why bird populations were declining due to hunting pressures.

Conclusion

The study found that large-bodied birds experienced the greatest declines, particularly in areas near hunter settlements, while small and medium-bodied birds were more affected near urban markets, likely due to commercial trapping for the pet trade. Human accessibility—including roads, markets, and settlements—was identified as a major driver of avian defaunation, shaping the intensity and patterns of hunting pressure. Among global regions, the Indomalayan realm (Southeast Asia) exhibited the highest levels of defaunation, followed by parts of West Africa and the Amazon. Notably, Brazil, China, and Indonesia emerged as major hotspots for the pet trade, whereas regions in Southeast Asia and West Africa showed high hunting pressure for food. Additionally, the study revealed that protected areas had limited effectiveness in preventing hunting-induced declines, highlighting the need for stronger conservation measures.