Invasive Species: Florida's Feral Monkeys Are Not Disturbing Ecosystem, Study Confirms

A group of small monkeys known as rhesus macaques have called central Florida's Silver Springs State Park home for decades, adapting to the region's wetlands from their original home in Asia. While locals enjoy feeding the feral animals, wildlife officials have been concerned about the impact they may be having on the local ecosystem.   

Concerns are often raised when invasive species, or nonnative animals, establish themselves in an area that is not equipped to support them, mostly due to a lack of space or food. In this case, Florida wildlife officials are concerned that human feeding is causing rapid overpopulation and that the monkeys may transmit diseases. 

The latest study from San Diego State University (SDSU) addresses these concerns by looking at the macaque's population size and frequency of human interaction. 

"The local authorities, like the Fish and Wildlife Service, have been less thrilled with the monkeys," Erin Riley, SDSU anthropologist and one of the study authors, said in the university's news release. "Their purview is to maintain a natural environment, and these animals are not natural to this area. They have concerns about the local ecological impact of these animals, and then there are also health issues if people interface and get close to them."

While a release stated that no one is certain when or how the animals were introduced, there is at least one existing theory that they are descended from monkeys brought to Florida during the filming of the various motion pictures about Tarzan, 1932-48. Surprisingly, researchers found the park's macaque population is actually smaller than previous estimates and that the vast majority of their diet comes from their environment rather than being offered by humans. Researchers estimate that a total of 118 rhesus macaques, living in four separate social groups, are present in the park and that only 12 percent of their diet consists of handouts from humans. 

The occasional boater may toss a monkey a whole orange every now and then, but the animals are picky about what offerings or provisions they accept. 

"They tend to ignore canoes and kayaks because people on those boats generally aren't the ones feeding them," Riley added. "It's the [people on the] big boats, the pontoons and the motorboats, that are feeding them. As soon as the monkeys hear the sounds of those boats, they come running up to the river's edge."

Generally speaking, the monkeys prefer eating leaves, buds, flowers, shoots and a type of dry fruit called a samara. However, researchers noted one novel, local adaptation:  The macaques enjoyed snacking on grass-like sprouts called sedges that grow in Florida's wetlands.

"From the park's perspective, they know that provisioning occurs, and their sense is that it's because of this provisioning that this population persists," Riley explained. "What our data shows is that provisioning actually doesn't occur that often anymore, and as a result the monkeys have learned to rely primarily on local food."

Since only two of the 611 human-monkey interactions observed involved direct contact, researchers also suggest their findings put to rest concerns of the monkeys transmitting diseases. However, increased education and outreach programs designed to discourage people from feeding the monkeys could benefit both parties, they added. 

The findings were recently published in the journal Primates.

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