Tropical rainforests around the globe are under intense, and increasing pressure, from hunting, according to a study released by researchers at Radboud University in Nijmegen.

The study, lead by Ana Benítez-López, mapped 4000 species and found that mammal populations have declined by an average of 83 percent, an bird populations by 58 percent in forests where humans have hunted. Researchers collected data collected over a period of 40 years, tracking mammal populations in hunted and unhunted forests.

The study found that numbers of medium sized mammals like moneys have declined of 27 percent in hunted forests, and populations of large mammals, like big cats and other large predators, and herbivores like elephants and rhinos have dropped more than 40 percent.

“Hunters target primarily large-bodied species because they provide relatively large meat yields and commercially valuable by-products such as horns and bones,” Benítez-López notes. “In addition, large mammals reproduce at slow rates, which means that it takes longer for their populations to recover when exploited.”