"For now, there is nothing that can be done to prevent the death of the primates," Sergio Lucena Mendes, a professor of animal biology at the Universidade Federal de Espirito Santo, told Seeker. "So far, the conservation community has been collaborating with a campaign to prevent people from injuring the primates in fear of yellow fever."
Strier added that some people do not understand that the monkeys are victims of the disease too. As a result, they are blaming the monkeys for the virus. The northern muriqui is among the most critically endangered primates on earth.
There are various species and subspecies of howlers, but the researchers believe that the recent deaths put many surviving howler populations at risk for extinction as well.
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"The monkeys actually act as sentinels, warning us when there's a disease outbreak that could affect humans," she said.
It is unclear why the howlers are so vulnerable to the virus, while the hippies and a close relative of them, spider monkeys of the Amazon and parts of Central America, appear to be more resistant.
Mosquitoes have been out in droves, possibly because rains following two years of severe drought prompted the hatching of eggs that remained dormant until the wet weather began.
Before the epidemic, the howlers and hippies had an uneasy co-existence. Howler monkeys are plant eaters too, so they would often eat much of the food in areas that the northern muriquis would pass through. The howlers additionally are very vocal, emitting screams and other loud vocalizations, including a guttural call that has been used in many horror films, as well as the Jurassic Park series.
The hippies, conversely, are a quieter bunch.