It's been a truly ferocious Atlantic hurricane season thus far in 2017: Harvey, Irma, Maria and Jose are already infamous cyclones, and more than 200 people have been killed from the Windward Islands to the Florida peninsula.

And now comes some bad news on the avian front in the wake of Irma: Audubon reports that the storm destroyed all of the active nests of the rare Florida (or Everglade) snail kite on Lake Okeechobee, that great 1,891-square-kilometre (730-square-mile) lake that historically overflowed south into the vast marshes of the Everglades.

A snail kite living up to its name. Image: Andy Morffew/Flickr

It's all the more of a blow to this highly specialised raptor – an indicator species in the imperilled and globally unique Greater Everglades Ecosystem – given the hurricane hit during a year of low all-around nesting rates.

"Before Irma, there had been only about 130 nests in Florida this year," Audubon explained, "so losing 44 new nests ended a poor breeding season on an even worse note."

The organisation notes that as much as 75 percent of the Florida snail-kite population didn't nest this year at all, likely due to a drier-than-usual winter dry season and an outright drought in the spring. Hurricane Irma's rains, meanwhile, swelled Lake Okeechobee's level by several feet – and it continues to rise in Irma's aftermath as the storm's dump of precipitation farther north drains into "Lake O" via the Kissimmee River watershed.

Thus, for the Florida snail kite, Audubon notes, "nesting in 2017 was harmed by both excessively dry and wet events."

Audubon surveys suggest many adult and juvenile snail kites weathered the hurricane, but the battering winds and downpours devastated eggs and hatchlings.

Snail kites are widespread in the Neotropics, but the unique Florida population, non-migratory and cut off from Caribbean and Central/South American birds, is endangered: as few as 800 of the delicate raptors survived in the Sunshine State in 2008.

Their precarious status in Florida has to do with the tunnel-vision diet – among the most tunnel-visionish of any raptor – that gives the birds their name. The kites mainly feed on apple snails, plucking these freshwater molluscs from just above or just below the water's surface and using their trademark hooked beaks to penetrate the shell. Apple snails are only fleetingly vulnerable to kites – mainly when they clamber up the stalks of emergent marsh vegetation to breathe, or to lay their eggs (though that's mainly a nighttime endeavour).

This means snail kites are tied to habitats where they can find and effectively hunt apple snails: lake margins, marshes and wet prairies without overly dense and obscuring vegetation, and with just the right amount of water.

Enter humans. Our modification of natural water regimes in central and southern Florida has cramped the snail kite's style, including in Lake Okeechobee. Though it's still vital hunting and nesting ground, the lake today offers less (and more precarious) habitat for both snail and bird thanks to the demands of South Florida's booming human population.

The snail kite's reliance on the sort of sodden but shallow open wetlands, and the seasonal rises and falls of water levels, that help typify the Everglades – nicknamed the "River of Grass" – has made the raptor a bellwether of the ecosystem. (The kite isn't the only specialist forager dependent on the subtleties of the intricate Everglades water cycle: one of the biggest native waders, the wood stork, times its breeding season to coincide with seasonal concentrations of fish in shallow dry-season pools, ideal conditions for pulling off its unique beak-probing ("tacto-location") method of hunting.)

Measures to restore critical habitat for the kite have helped increase its numbers since the mid-2000s. An invasive relative of the Florida apple snail, the island apple snail of South America now established in many local waterways, is a mixed message for the snail kite: the birds do find a ready food source in this prospering exotic, but only the smaller ones; island apple snails grow larger than their native Florida relatives, and kites seem less inclined to eat full-sized specimens.

It's worth noting that hurricanes are a regular element of the Greater Everglades ecosystem, and, before modern flood-control infrastructure, their voluminous rainfall (along with summer thunderstorms and other wet-season deluges) helped periodically pulse Lake Okeechobee floodwaters southward through the sawgrass mires of the Everglades. (Otherwise, the main input for the River of Grass is direct rainfall, which makes this huge tropical "sheetflow" wetland unique in the world.)

Here's wishing Florida's snail kites a more auspicious nesting season next year. Meanwhile, check out some fabulous photos and footage of the graceful little hawks on the hunt in this Audubon Magazine feature from earlier this year.



Top header image: Dan Irizarry/Flickr