Howler monkeys in southeast Mexico are dropping dead from the trees suddenly prompting authorities to investigate the matter, CBS News reported Tuesday.

Local authorities have estimated that as many as 85 monkeys have died in this mysterious way, the outlet reported.

The Mexican environmental ministry issued a press release Monday informing the public that they were exploring multiple potential causes behind the deaths. “To date, various hypotheses are shared about the reason for these deaths, such as heat stroke, dehydration, malnutrition or fumigation of crops with pesticides, so studies will also be carried out to determine the cause,” the government said in the press release.

The ministry also mentioned the possibility of “any type of virus or disease” being involved in these deaths and stated they are testing for it, the press release said. Mexico said that anyone who came across a dead monkey should notify the appropriate authorities, the press release read.