But relying on a non-native ‘surrogate’ can have detrimental impacts on an ecosystem, expert says
Since island apple snails invaded the Florida Everglades, an endangered species of bird known as the snail kite has bounced back from the threat of extinction.
It's a rare case of a destructive invasive species having a positive impact, says Robert Fletcher, a professor of landscape ecology at the University of Florida who also directs a snail kite monitoring program.
"There was a lot of concern that this bird that was already endangered was really on the brink of extinction. And then entered this non-native snail," Fletcher told As It Happens host Nil Köksal.
The Everglade snail kite is a hawk-like raptor that relies on wetland ecosystems to feed almost exclusively on Florida apple snails.
In the early 2000s, severe droughts in the Everglades caused the population of these local apple snails to dissipate. And since snail kites relied on them as their sole food source, their numbers plunged from more than 3,000 birds in the late '90s to approximately 700 in 2009, according to a 2022 report by the conservation organization Audubon Florida.
Birds adapt to new prey
Cue the non-native island apple snail.
After they showed up in the southeastern United States, the snail kite population in Florida bounced back to approximately 3,000 birds today.
But when the non-native snail was first spotted in 2004, Fletcher said people were very worried that it was "going to exacerbate the extinction risk of [the snail kite] and essentially really push it even closer to extinction."
The main concern was that these non-native snails were up to five times bigger than what the birds were used to capturing with their talons and extracting with their bills.
"Scientists quickly saw snail kites trying to forage on this non-native snail, but they were largely unsuccessful. They would drop the snails quite often," Fletcher said.
Once the non-native snails had expanded through much of the Everglades and overtaken the native ones, however, the snail kite population began to rise.
And the birds who bred in wetlands with the invasive snails fared far better than birds forced to survive without them as a source of food, says Fletcher.
"It was incredibly surprising," he said. "We couldn't understand how the birds were handling such large snails."
He and his students had been monitoring the snail kites for years, banding them as they fled from their nests in order to measure many things about them, including the size of their bills.
The data they'd been collecting showed their bills were getting bigger every year in order to accommodate the baseball-sized snails.
What this means for the local ecosystem
Samuel Chan, an invasive species expert at Oregon State University, says the island apple snail from South America likely got loose and established themselves in Florida through the pet or aquarium trade. Since this species of snail was more resilient to dry conditions, it out-competed the native species and took over.
Although the snail kite's emerging recovery is good news, it appears to be almost completely based on the occurrence of exotic snails, Chan said. The bad news, he added, is the native snails have not made a comeback.
"I think the birds are telling us a story about what's missing in their habitat," he said. "The reality is that this invasive species is filling a hole, but there will be repercussions in other layers of the ecosystem."
Chan referred to the non-native island apple snail as a "surrogate" food source for the snail kites, which have adapted their feeding as a survival strategy.
"But a surrogate host can't be a solution. It's not just saving the snail kites; it's doing other things, too. And that's the part that is worrisome. The surrogate is not going to stay still," Chan said.
Fletcher admits it's a complicated situation and he also has concerns about the potential impact the species will have on the Everglades in the long term.
While the island apple snail may appear to be saving the snail kite, it is known to be destructive, Fletcher says. It has decimated agricultural fields and feasted on aquatic vegetation in many areas of the world.
"It's a tricky one," he said, "because depending on the situation, there can be lots of lots of consequences when new species come into areas — but sometimes there can be benefits."
Fletcher and Chan both refer to the Florida apple snail population as a barometer for the health of the local ecosystem.
In order for the snail kite's comeback story to have a happy ending, says Chan, native diversity and resilience is required. If the endangered bird continues to rely exclusively on non-native invaders, there could be detrimental impacts on its ecosystem.
"If we're going to recover the native snail kite, we need to recover the native snail," he said.
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