Howler monkeys are ‘falling out of trees like apples’ in Mexico as the nation endures a severe heatwave.
So far the number of deaths of the species has been recorded at 147.
In the first recorded incidents 83 of the primates, known for their roaring vocal calls, were found dead in the Gulf coast state of Tabasco, with the deaths linked to climate change issues including heat, drought and deforestation.
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.’
The animal doctor put ice on their limp hands and feet, and hooked them up to IV drips.
So far, the monkeys appear to be on the mend, and are exhibiting more of their usual characteristics. They are now in cages at Valenzuela’s office.
He said: ‘They’re recovering. They’re aggressive, they’re biting again,’ he said, noting that was a healthy sign for the creatures.
Monkeys falling like apples
In the first reports of the deaths, wildlife biologist Gilberto Pozo counted 83 of the animals dead or dying on the ground under trees.
‘They were falling out of the trees like apples,’ he said. ‘They were in a state of severe dehydration, and they died within a matter of minutes.’
He attributes the deaths to various environmental causes including abnormally high heat levels, drought, forest fires and logging that deprives the monkeys of water, shade and the fruit they eat.
Also the falls from metres up in the tree canopy inflicted additional damage that often finally killed the already sick and injured animals.
‘This is a sentinel species,’ Pozo said, referring to the effect where what is happening to one species can say a lot about an ecosystem. ‘It is telling us something about what is happening with climate change.’
Pozo’s group has set up a special recovery stations for monkeys – it currently holds five monkeys, but birds and reptiles have also been affected – and is organising a team of specialised veterinarians to give the primates the care they need.
Mantled howler monkeys are one of the largest primates in Mexico and Central America. They eat fruit and leaves, which are also one of their main sources of water.
‘Though species have evolved to adapt to different conditions, things are now changing so fast, that it’s going to be very difficult for many species to adapt. There is not enough time.’
Dr Liliana Cortés Ortiz, Primatologist, University of Michigan
The species, which is found as far south as Peru, is considered vulnerable by the International Union for Conservation of Nature. But the Mexican subspecies is in worse shape and has been classified as endangered.
This isn’t the first time this species of howler monkeys has been in danger. In 2016, a similarly hot and dry year, mass die-offs of howler monkeys were also reported in Nicaragua. At the time, scientists estimated at least 280 had animals died in three months, though they were unable to pinpoint the cause.
Researching the cause
Now, scientists from the region are forming a working group to put together protocols that lay out what people should and shouldn’t do if they find monkeys in distress. They are also trying to attract funding to do more research into the causes of the deaths.
Dr Liliana Cortés Ortiz, a primatologist at the University of Michigan and the vice chair of the primate specialist group at the International Union for Conservation of Nature said she worried about what could be happening to other species that people aren’t as likely to notice.
‘Though species have evolved to adapt to different conditions, things are now changing so fast, that it’s going to be very difficult for many species to adapt,’ she said. ‘There is not enough time.’
In May nine cities in Mexico set temperature records, with Ciudad Victoria, in the border state of Tamaulipas, registering 47C. Across the country more than 20 human casualties have been linked to the heat.
