Howler monkeys are dropping dead from trees in southeast Mexico’s tropical forests, and authorities said Monday they were investigating whether extreme heat was killing the endangered animals. Officials have not given an exact death toll but local media outlets report that as many as 85 primates have died.

According to the environment ministry, causes under consideration include “heat stroke, dehydration, malnutrition or fumigation of crops with pesticides.”

The ministry said studies would be carried out to rule out a virus or disease.

Temperatures up to 113 degrees Fahrenheit have been recorded in the southern states of Chiapas and Tabasco, where the deaths have been reported.

The Tabasco-based wildlife preservation group COBIUS has reported “mass deaths” of primates.

“It’s very likely due to climatic reasons, but we cannot rule out other important causes,” the organization said in a statement, adding an appeal to the public: “If you see monkeys that are weak and apparently suffering from heat or dehydration, please try to hoist a bucket of water by rope for them to drink.”

According to National Geographic, howler monkeys live in Central and South America and rarely leave the treetops where they feed in the forest canopies.

A source from Tabasco’s Civil Protection agency told the Reuters news agency that monkeys have died in three of the state’s municipalities.

President Andres Manuel Lopez Obrador, who is from Tabasco, also pointed to extreme heat as the likely cause.

“The heat is very strong. Since I’ve been visiting these states, I’ve never felt it as much as I do now,” he told reporters.

Authorities and conservationists have been carrying out patrols to provide water and food, mainly fruit, to help monkeys stay hydrated, the Tabasco civil protection institute said.

Earlier this month, Mexico reported record-high temperatures in 10 cities, including the capital. 

The soaring temperatures come as the country is also grappling with severe drought and a water supply crisis. Mexico City — home to nearly 22 million people — has been suffering from diminishing water supplies — and experts say it’s on the verge of being unable to provide sufficient fresh water to residents.