Monkeys in Costa Rica are Turning Yellow, and Researchers May Know Why

Over the last five years, black mantled howler monkeys in Costa Rica have been showing up with bright yellow patches of fur, and researchers are beginning to think they know why.

While mantled howler monkeys usually sport a kind of melanin – the coloring that shows in hair and skin – that's black, dark brown or gray, research in the journal Science suggests the monkeys could have had their melanin changed to pheomelanin — a type that contains sulfur.

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"Costa Rica in Central America has one of the highest intensities of pesticide use in the world, averaging over (55 pounds) applied per hectare (about 2.5 acres) of cultivated land," said the Pesticide Action Network. "Pesticide use is particularly high on important export crops, e.g. banana, pineapple, melon and coffee."

Scientists believe the change in color could negatively affect the monkeys. With a brighter pigment, they could be easier for predators, such as jaguars, to locate against dense forestry.

The research team believes the coat color might be something that's only getting started and could spread. Some monkeys are already showing coats that are primarily yellow, researchers wrote in Mammalian Biology, where their full results will be published.