At least 83 of the medium-sized primates, which are known for their loud vocal calls, were found dead in Tabasco state on the Gulf coast. Others were rescued by residents, including five who were rushed to a local vet, who fought to save them.

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

While Mexico's brutal heat wave has been linked to the deaths of at least 26 people since March, veterinarians and rescuers say it may have killed hundreds of howler monkeys.

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

Wildlife biologist Gilberto Pozo counted about 83 of the dead animals under the tree. Their die-off began around May 5 and peaked over the weekend.

"They were falling from the trees like apples. They were in a state of severe dehydration and died within minutes," Pozo said.

Pozo attributes the deaths to factors such as high heat, drought, forest fires and logging. By May 9, at least nine cities in Mexico had set temperature records, with Ciudad Victoria, in the border state of Tamaulipas, reaching 47 degrees Celsius.