University of Florida graduate student Chris Cattau holds shells from a native Florida apple snail (right) and a much larger invasive species. Both snails are eaten by an endangered bird, the Everglades snail kite. But a UF study suggests juvenile kites may starve while trying to subsist on the hard-to-handle invasive snails. (Credit: Tyler Jones/University of Florida/IFAS)

U. FLORIDA (US)—A huge South American snail is wreaking havoc on its predator, the snail kite, an endangered Everglades bird of prey.

The bird usually feeds on native apple snails that are about the size of a golf ball, but those snails have declined in historically important kite habitat and the birds have fled.

Many kites now dwell at Central Florida’s Lake Tohopekaliga, which is filled with the larger invasive island apple snails.

Researchers at the University of Florida warn that because the mollusks grow larger than a tennis ball, juvenile kites have difficulty holding them and as a result, may become malnourished.

The study was published in the current issue of Biological Conservation.

Popular in the aquarium trade, the island apple snail may have been accidentally or deliberately released in the wild. It’s been found in numerous Florida locations, according to the state Fish and Wildlife Conservation Commission.

As the invader spreads, it could become a serious threat to snail kite populations, says Wiley Kitchens, a courtesy professor with UF’s Institute of Food and Agricultural Sciences.

Fewer than 700 of the birds exist in the U.S., all of them in Central and South Florida.

“There’s an 80 percent probability that in the next 30 years, snail kites will be extinct in the U.S., for all practical purposes,” Kitchens warns.

But management efforts by state and federal agencies offer hope.

The snail kite is important to scientists because it’s one of the few vertebrates whose range is largely restricted to the greater Everglades ecosystem, Kitchens explains.

He considers it a barometer for the region’s environmental health and success of Everglades restoration efforts.

Adult kites have trouble handling island apple snails but got enough to eat. Juvenile kites have more difficulty, possibly because they’re less experienced at holding and devouring prey.

The younger birds dropped invasive snails eight to 10 times more often than native snails, and it took them four times longer to attempt to eat the invasives, says Chris Cattau, a graduate student working with Kitchens.

The study suggests juvenile kites on a steady diet of invasive snails might burn more calories than they consume because they expend so much effort trying to eat the snails, Cattau says.

“In some cases this could impact survival,” Cattau says, who co-wrote the paper.

Researchers predict that if Lake Toho remains a popular kite breeding area, it may become an ecological “trap,” providing too little food for young birds and raising their mortality rate.

In Florida, the invasive and native apple snails have rarely been found side-by-side, says Phil Darby, associate professor at the University of West Florida and an expert on apple snails. So it’s hard to say if the invader will displace native snails.

In any event, Darby says, native apple snail populations must be brought back in historically important kite habitat if the birds are to return there.

“They’re flexible,” he says. “Kites will show up where the food sources are most abundant.”

The research was funded by the U.S. Corps of Army Engineers.

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