Two University of Michigan-based scientists are leading an effort to explain the recent deaths of at least 75 howler monkeys living in the tropical forests of southwestern Nicaragua.

Liliana Cortés-Ortiz and Kimberly Williams-Guillén are assembling a multi-institution team of experts to test various scenarios that might explain the Nicaraguan deaths, which come on the heels of smaller howler monkey mortality events in Ecuador and Panama.

At least 75 deaths have been confirmed through reports by Nicaraguan landowners and forest rangers, 70 of them since mid-January.

At this early stage, the researchers have four main cause-of-death hypotheses they'd like to investigate. They want to know whether the deaths were caused by: 1) drought or some other environmental stress resulting in lack of food or water; 2) poisoning by ingestion of plants containing high levels of toxic compounds; 3) pesticides or some other form of environmental contamination; or 4) a pathogen such as a mosquito-transmitted virus like yellow fever or Zika.

"We don't know why this is happening, and we need to find out," said Cortés-Ortiz, a research associate professor in the U-M Department of Ecology and Evolutionary Biology who studies primate evolution. "So we are putting together a team of experts to test all possible scenarios in the three countries where howler deaths have been reported."

Cortés-Ortiz has studied howler monkeys in Mexico, Panama and Peru. She is the Mesoamerican regional coordinator of the Primate Specialist Group, which is part of the International Union for the Conservation of Nature.

"It is critical to conduct the proper tests and analyses to identify the cause of death for these howler monkeys and to understand whether the deaths in the different countries are related," she said. "At the same time, we need to avoid unfounded speculation and wait until we have solid information."

The paper received widespread international media attention, including the following: Fusion, Science, Nature World News.

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