MEXICO CITY (AP) Its so hot in Mexico that howler monkeys are falling dead from the trees.

At least 138 of the midsize primates, who are known for their roaring vocal calls, were found dead in the Gulf Coast state of Tabasco since May 16, according to the Biodiversity Conservation of The Usumacinta group.

Others were rescued by residents, including five that were rushed to a local veterinarian who battled to save them.

They arrived in critical condition, with dehydration and fever, said Dr. Sergio Valenzuela. They were as limp as rags. It was heatstroke.

While Mexicos brutal heat wave has been linked to the deaths of at least 26 people since March, veterinarians and rescuers say it has killed dozens and perhaps hundreds of howler monkeys. Around a third of the country saw highs of 45 degrees Celsius (113 degrees Fahrenheit) on Tuesday.

In the town of Tecolutilla, Tabasco, the dead monkeys started appearing Friday, when a local volunteer fire-and-rescue squad showed up with five of the creatures in the bed of a truck.