In tropical forests, bird and mammal populations are significantly lower - 53% and 82% respectively - in areas where hunting occurs, a new study finds. In many forests that appear structurally undisturbed, hunting can exert a major pressure on wildlife, causing large declines in populations. To better understand the impact of hunting in tropical regions, Ana Benítez-López et al. analyzed 176 studies, which collectively represent 97 bird and 254 mammal species in South America, Asia and Africa. They used the data to estimate the overall reduction in mammal and bird abundance in hunted compared with unhunted sites. Not only did they find that bird and mammal populations were significantly reduced in hunted areas, but that there is a direct relationship between population reduction and distance from hunters' access points, urban trading markets, and protected areas. For example, even though mammal population densities were higher inside protected areas than non-protected areas, nearby hunting practices still had a negative impact on mammal abundance within the protected regions. Strategies to sustainably manage wildlife hunting in both protected and unprotected tropical ecosystems are urgently needed to avoid further defaunation, the authors say. Smaller mammals were consistently more abundant in places with higher hunting pressure than larger species, which the authors say is probably because these species experience an ease of predation pressure and competition as a result of humans hunting more desirable medium- and large-sized mammals. These results are highlighted in a Perspective by Justin S. Brashares and Kaitlyn M. Gaynor.