Rhesus macaques may be preying on bird eggs in Silver Springs

A group of UF/IFAS researchers used camera traps next to 100 artificial bird nests baited with quail eggs near the Silver River. Researchers placed nests in shrubs and left them for 12 days, which represents the incubation period of many of the park's songbirds, like Northern Cardinals.

Rhesus macaques preyed on 21 of the 100 nests, the study showed. Creatures other than macaques preyed on another nine nests and an unidentified predator ate eggs from five nests. The study results do not suggest rhesus macaques are destroying 21 percent of native bird nests, said Steve Johnson, a UF/IFAS associate professor of wildlife ecology and conservation.

However, the study does confirm rhesus macaques in Silver Springs State Park will consume eggs when they find them in natural habitat, Johnson said.

"Our study shows that we need to learn more about their habits and impacts in the park so the Florida Park Service can make science-based decisions on how to manage these non-native monkeys," he said.

"Monkeys are cute, but can devastate systems that don't have the proper predators or other ecological means to keep their populations in check," said Jane Anderson, a doctoral student in wildlife ecology and the lead author on this study.

Silver Springs State Park provides a natural habitat for numerous species, including 18 endemic and 10 endangered plant species, as well as habitat for resident and migratory birds, according to the Florida Department of Environmental Protection.

While the non-native rhesus macaque resides in Silver Springs State Park, the rest of Florida is home to more non-native wildlife species than any other state. It costs $500 million annually to prevent, manage and mitigate those invasive species, according to previous research cited in the new UF/IFAS study. Florida is particularly vulnerable to non-native species because of tourism, ports and a thriving exotic pet trade, among other factors.

In places where they've been introduced by people, macaques have increased bacteria in water, destroyed mangrove trees -- leading to shoreline erosion -- caused millions of dollars in crop damage and threatened native wildlife populations. When they're put in non-native habitats, macaques prey on nests.

As for Silver Springs State Park, about 190 macaques lived in the park as of the fall of 2015, the study says. However, there are no management strategies or population control measures for the animals. By not removing macaques from the park, park managers risk allowing their population to increase, and scientists don't know how that would affect native species.

Rhesus macaques could potentially impact the native plant and animal species in the park in several ways; for example, eating plants needed by other animals, changing the plant composition in the park, or pushing other animals out of the habitat by being aggressive, Anderson said.

"There are lots of things that could be tested, so the nest study was just one of the things that needed to be considered," she said.

The new study, co-authored by Johnson, Anderson and other UF/IFAS researchers, is published in the journal Biological Invasions.