Rare bird's growth might be bad news

An invasive giant snail is a feast for the snail kite population, but could hurt Florida's sensitive Everglades

The endangered Everglade snail kite has found a new source of food that could be changing the way researchers monitor Florida's sensitive ecosystem.
Dario Sanches

MIAMI -- Humberto Jimenez is looking for a special place in the marsh. Barely a mile from the Tamiami Trail, the 275-mile stretch of road famous for cutting off the historic southward flow of Florida’s River of Grass, he maneuvers his airboat around the tiny tree islands that punctuate the Miccosukee Reservation near Miami.

After 14 years as a non-native guide for the Tigertail Airboat Tour Co., he knows where to find rare animals in the protected wilderness bordering the Big Cypress National Preserve.

Circling in the sky, a raptor bird scans the water for its next meal. It’s an endangered Everglade snail kite, and it’s looking for a certain mollusk. That’s because the kites are picky eaters and eat only freshwater apple snails. Gliding over the marsh close to the surface, the bird plucks a snail in its talon. In early spring, Jimenez spotted more than a half-dozen of the extremely rare birds foraging for food.

“Now it’s real easy to find them. I’m seeing twice as many kites as before,” he said.

The imperiled snail kite’s resurgence in Florida’s vast Everglades region should spell good news, but wildlife biologists aren’t celebrating. Like the proverbial canary in the mine, this rare bird is an indicator species of appropriate water levels in the Everglades. When the levels rise too high, the birds’ food disappears. Too low, and drought conditions encourage the kites to abandon their nests. Like a Goldilocks of the Glades, they need the water levels to be just right, and what’s good for the kites is usually good for the Everglades and humans.

But a new, invasive giant mollusk could be the reason for the snail kites’ increasing numbers -- and could be throwing off the way researchers track the health of the sensitive environment.

The larger island apple snail is twice the size of the native apple snail, making a heartier treat for snail kites.
Patricia Sagastume

While still below “historic or safe levels,” according to a U.S. Corps of Engineers study, the snail kite appears to be in much better shape than it was five years ago. As suburban sprawl, agriculture and industry uses expanded, the bird’s population dwindled to the point where there were no kites to be seen in their historic nesting grounds by 2000. Now the kite population is exploding -- and it’s not because Everglades recovery projects are working.

“We’ve had more than 400 kite babies, so that’s great news,” said Paul Gray, a biologist for Audubon Florida. “What troubles us is that the kite comeback is almost all with these exotic snails.”

Throughout Florida’s marshes and canals are foreboding signs of a new species spreading uncontrollably. Pink-bubble-gum-colored sacs of tiny egg clusters cling to plant stalks that protrude above the marsh. They’re the eggs of the island apple snail, Pomacea maculata.

Several species of the South American snails were first observed in the late 1980s, but in the last two decades the mega-mollusk maculata outproduced all the others and spread rapidly. It’s suspected that these baseball-sized creatures were unwanted aquarium pets released near the Miami and West Palm Beach canals. Now these meatier snails, which are about twice the size of the native apple snail, are ensconced in lakes and canals from northern Florida to as far south as Everglades National Park. At the same time as this new species is spreading, the native apple snail population is shrinking.

Scary clues

Discarded apple snail shells sit in a snail kite nest.
Patricia Sagastume

The nomadic snail kites have recognized the heftier replacement and followed the food source.

There are scary clues about what these big mollusks can do in small marsh areas. The exotic snails desimated plant life near lakes and ponds near Tallahassee. This overconsumption of vegetation has not spread to the wetlands, or at least has not been noticed yet. 

“So far we haven’t seen any of that (consumption) in the wetlands the kites use,” said Philip Darby, a biology professor at the University of West Florida (UWF). For 15 years, he has collected data for the UWF Apple Snail Project by sampling the conservation area between Tampa and Miami. He said the verdict is still out on why the native apple snail population dried up in the first place, but the mystery doesn’t stop there.

Mysterious impact

“We are not seeing a situation where the native snail was abundant and then, all of a sudden, it disappeared because the exotic showed up. None of that has happened,” said Darby. He admits the current intense focus on exotics has him worried.

“Maybe complacency is too strong a word, but there’s not intense concern about the kite because the exotic snail is providing enough food,” he said. “But the native snails are disappearing. They’re 10 times lower than they were in a lot of these areas.”

More research is needed to illuminate exactly what these invasive snails might do. Researchers worry whether nutrient-rich marshes with the presence of these exotic snails are in danger of being stripped of their aquatic vegetation, or what happens if the native snails, once the sole diet for the endangered raptors, completely disappear. Also, since it's not known exactly how these non-native snails spread so quickly, there is the possibility they could surpass a sustainable level in the Everglades, and if that were to happen, what could it mean to wildlife?

A snail kite coordinating committee has been formed, and this fall the small community of snail experts will present its work on kites, snails and other related topics. 

With the peak of the hurricane season around the corner, water managers have started regular releases of millions of gallons of water from Lake Okeechobee to keep water levels safe for humans and wildlife. Because the raptor bird is federally protected, the feds have a mandate to preserve places where its food source survives, namely the Everglades and Lake Okeechobee. But these invasive snails, which can survive long periods of drought and flood situations, have upset the hydrology formula that wildlife and water managers have relied on.

"Last year, the National Academy of Sciences gave snail kite management an F (grade) because Lake Okeechobee and other water-conservation areas were wrecked," said Gray. "Now we have a snail that doesn’t get wiped out in our human-amplified water events, so the snail kites aren’t a sensitive indicator as they used to be.”

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