Biologist Gilberto Pozo was observing a grove in the southern Mexican town of Cunduacán in early May when two caped howler monkeys leapt from a tree in front of him with a thud. It fell.
“They showed signs of dehydration and were treated,” he said. “But they didn’t survive.”
At first, Dr Pozzo and his team at the non-profit conservation group Cobius thought the monkeys had been engulfed in smoke by fires started by farmers clearing nearby land.
But in recent weeks, with temperatures soaring above 100 degrees Fahrenheit, reports have begun to surface of dozens of monkeys dying. Residents found more than 10 dead at once, many of them showing signs of dehydration. As of Wednesday, 147 monkeys had died in the southern Mexican states of Tabasco and Chiapas.
The deaths of dozens of mantled howler monkeys in Mexico may be the latest sign of the danger extreme temperatures pose to wildlife around the world. As global temperatures break records, scientists have recently documented the extinction of Amazon dolphins and mass bleaching events in coral reefs around the world.
Dr. Pozzo said of monkeys, “Animals are the sentinels of the ecosystem, so they are sending us a warning.” “If you’re not feeling well, it’s because something is going on.”
Scientists investigating the death still don't know exactly what caused it. But they hypothesize that warmer temperatures, combined with a confluence of other factors, including fire, deforestation and logging, may have confined the monkeys to small forest areas with little shade, food and water. Scientists have not yet ruled out a pathogen, but a recent autopsy of one of the monkeys showed no signs of influenza, including avian flu or Covid-19, Dr. Pozzo said.
Mantle howler monkeys are one of the largest primates in Mexico and Central America, averaging about 25 inches in size. They are covered in thick, black fur and are known for their low, guttural calls. They eat fruits and leaves, which are one of their main sources of water. Scientists suspect that the drought is causing leaves and streams to dry out, making it more difficult for the monkeys to stay hydrated.
This species, found in southern Peru, is considered vulnerable by the International Union of Conservation of Nature. However, the Mexican subspecies is in worse condition and has been classified as endangered.
In Mexico, a heat wave has brought drought to much of the country and water shortages in the capital. Environmental changes have likely placed greater stress on Mexico's small mammals. Tabasco State is home to most of Mexico's cattle and is one of the most deforested states in Mexico. As farms increased in the area, the rainforest inhabited by monkeys decreased.
“Howler monkeys in general are very resilient to these conditions and can survive for long periods of time,” said Liliana Cortés Ortiz, a primatologist at the University of Michigan and vice president of the International Union for Conservation's Primate Expert Group. ) said. nature.
Videos of dead monkeys gathered in groups on the ground and baby monkeys limping have spread across social media in recent weeks. “Anyone setting fires, please stop,” one person said in a video posted to Facebook.
The deaths sparked a response on Monday when President Andrés Manuel López Obrador told reporters the government was exploring ways to help. “It was really hot.” He said. He added that on a recent visit to some of the states, he “never felt this bad.”
This is not the first time this howler monkey species has found itself in trouble. Likewise, in the hot and dry year of 2016, mass deaths of howler monkeys were reported in Nicaragua. At the time, scientists estimated that at least 280 animals died over a three-month period, but the exact cause could not be determined.
Now scientists in the region are forming a working group to draw up protocols outlining what people should and should not do if they spot a monkey in distress. They are also trying to attract funding to conduct more research into causes of death.
Dr. Cortes Ortiz said he worries about what might happen to other species that people don't notice.
Although species have evolved to adapt to a variety of conditions, things are now “changing so quickly that it will be very difficult for many species to adapt,” said Dr. Cortés Ortiz. “There’s not enough time.”
Currently, non-profit and academic groups in Mexico are caring for any monkeys they can find. More than a dozen people are being hydrated and receiving treatment at the clinic. Some are recovering in Cunduácan, the city where Dr. Pozzo first saw animals falling from trees. But on Wednesday, he said, “sadly one of them has passed away.”