The Everglades snail kite, a raptor with red eyes and a knife-sharp beak, was sinking into oblivion a decade ago, its graceful arc on mottled wings fading from Florida skies forever.
As humans watched the free fall with haphazard rescue attempts, an unwitting savior stalled the extinction countdown.
In a strange twist to Florida’s storied tale of defeat in the face of invasive species, an exotic snail considered harmful for its voracious appetite and proficient procreation is propping up the raptor population.
For once, a struggling Sunshine State local is benefiting from an invasive import.
“It’s a really strange situation,” said Zach Welch, a lead scientist and snail kite expert with the South Florida Water Management District. “We’re certainly not looking at imminent extinction like we were before the snail invasion. Instead, we have an invasive species helping an endangered species.”
In 2010, the number of successful snail kite nests statewide through May totaled six.
This May, the number of successful nests was 124.
But the relationship between the endangered snail kite and its invasive prey presents a unique conundrum for wildlife managers: How do you control the rapid expansion of an exotic species that can invade farms and may be competing with Florida’s native snail while still allowing the snail kite to prosper?
“It’s all good if you are a snail kite, but I think there could be a cautionary story here about stepping back to look at the big picture,” said Tim Collins, a biological sciences professor at Florida International University. “It’s probably not good news if you are a native snail.”
Federal protection was needed for the bird
The exotic snail, a freshwater gastropod called commonly the “island” or “channeled” apple snail, was likely brought to the U.S. for fish tank adornment.
Its softball-size bulk, year-round egg-laying capability, and resilience to high-nutrient water is like Popeye’s can of spinach to the medium-sized bird of prey, extending its nesting season, hatching stronger fledglings and growing bigger adults.
A study released in December by University of Florida researchers found one more remarkable unintended result — a rapid microevolution of the snail kite to have larger beaks more adept at digging deep into the meaty whorl of the exotic snail.
“In terms of other species being supported by exotics, I don’t know of too many situations quite like this,” said Robert Fletcher, an associate professor of wildlife biology whose University of Florida lab monitors snail kite nesting and growth. “It’s hard to know if the number of kites would have gone down further, but everything points to the positive changes being based on this increased food base.”
It’s been 50 years since the distinctive orange-legged Everglades snail kite was on the first list of animals given federal protection under the 1967 Endangered Species Conservation Act.
At the time, just 21 birds were counted in South Florida in a habitat range known to extend from the Kissimmee basin north of Lake Okeechobee to the Keys. While the count was likely skewed by limited resources and an inability to reach deep into habitats, there was no doubt the kite was in trouble.
Its fate was tied in an evolutionary cascade to the golf ball-size native Florida apple snail, a nutrient-sensitive mollusk with a short lifespan and limited egg-laying season. The kite’s distinctive curved beak is uniquely built to snake into the apple snail’s shell, cut the muscle and scoop out the flesh.
The male kite, which has slate gray feathers as compared to the brindle pattern of its mate, is slightly smaller than the female. But both have short legs that allow them to only grab snails in shallow water, or when the snails come to the surface to breathe or lay eggs. If the land dries out, the snails burrow into the ground where the birds can’t reach them.
The draining of Florida’s natural wetlands to build homes and farms hurt the native apple snail, which still struggles in water high in nutrients from fertilizer runoff. Snail kites mirrored the apply snail’s decline.
“Everything for these birds revolves around the food,” said Tyler Beck, snail kite conservation coordinator for the Florida Fish and Wildlife Conservation Commission. “If there are lots of birds, it means there is a lot of food.”
Wetlands restoration helped buoy snail kite numbers from the 1967 count to 3,400 in 1999. But a punishing 2008 drought dropped the numbers to a frightening 750 birds.
“Real alarm bells went off,” Fletcher said.
Empty shells are evidence of the raptor’s appetite
Four years earlier, however, the invasive snail began establishing itself in the snail kite’s breeding range, Fletcher said.
Collins, the FIU biological sciences professor, said there are five species of snails in Florida, only one of which is a native.
“The exotics are very large animals and kind of impressive,” Collins said about why people may have wanted them for fish tanks. “They produce a lot more offspring.”
While a native Florida apple snail may produce up to 100 eggs in a clutch, the exotic snail could lay more than 1,000. In the Rotenberger Water Management Area south of Lake Okeechobee last week, wads of bubble gum-colored egg clutches from the exotic snails clung to vegetation while empty shells were evidence of the kite’s appetite. When Rotenberger began to dry out this year, the South Florida Water Management District opened a pump station to its north to allow more water in through the Miami Canal.
“We are doing a better job of maintaining habitat for the birds, and that includes proper water levels, but I can’t downplay the significance of this exotic snail giving them a big boost,” Beck said.
The snail kite population this year is estimated at 2,585.
Fletcher can’t say for certain whether the kite population would have rebounded without the exotic snail, but the year-round food source has increased nesting periods from a few months in the spring well into fall, and made the birds more willing to start new nests if one fails.
“We don’t know the future,” Fletcher said. “I think what this situation has done is it’s given us a bit more breathing room to better understand how to appropriately manage the greater Everglades for snail kites.”