Earlier this month, an orangutan was found brutally shot to death in Borneo. In January, one was found decapitated and floating in a river. In 2017, oil plantation workers were accused of killing and eating one of the island's orangutans.

These stories are examples of small, incremental intentional killings of the island's endangered species. But according to a new study, published in the journal Cell Biology, such losses are adding up—contributing to the overall, long-term decline of a fragile species.

The comprehensive study pulled from data collected by 38 different research organizations. When Maria Voigt, the study's lead co-author and a researcher from the Max Planck Institute for Evolutionary Anthropology and the German Center for Integrative Biodiversity