If you want to study alligators, there may be no better place than the Tom Yawkey Wildlife Center on the coast of South Carolina. Researchers have been studying local populations of American alligators there for over three decades. The result: an unprecedented level of understanding about the big reptiles' lifestyles and reproduction, as well as the changes that go on throughout the animals' lives.
Gator researcher Phil Wilkinson started studying the Yawkey gators back in the late 1970s. Originally, he and his colleagues were interested in nesting habits: they wanted to get an idea of how often the alligators laid eggs and how many babies they had, and to use that information to estimate the size of the local population. But once the team got started on studying their reptilian subjects, they just kept going.
As the years went by, the scientists got to know the locals well, and colourful names like "Truck Biter" (named for doing just what his moniker suggests) and "Grover" (after former US President Grover Cleveland) inevitably followed. The team eventually realised they could recapture the same animals multiple times and gain insight into their life story.
From 1981 to 2015, the researchers continued to monitor around fifty different gators (19 males and 31 females) living on two of the islands in the 24,000-acre reserve. Their results, published in the journal Copeia, reveal how gators grow – and when they stop.
"You can't really know how long wild alligators live and grow unless you have an animal that was caught 20 or 30 years ago and you catch it and measure it again," explains Thomas Rainwater of Clemson University, one of the researchers involved in the study.
There's a common myth that crocs and gators simply never stop growing, but it's well-known among herpetologists that this isn't necessarily true. Just when their growth ceases, however, isn't fully understood. The Yawkey study found that after a few decades, females reached a maximum size of around 2-3 metres (7-10 feet), and males at 3-4 metres (10-12 feet). After that point, the animals could live quite a long time without getting any bigger.
"Our study shows that, at least in Yawkey, adult alligators stop growing before they die," Rainwater says. "We have animals that Phil [Wilkinson] first caught and tagged back in 1981 that we recaptured in 2016 and they are still exactly the same length they were 35 years ago."
Another important insight of this long-term project involves mama gators. Despite a widespread belief that females do their best egg-producing at middle age (and then their reproductive abilities decline as they grow older), the study found that females reached maturity in the mid-teens and continued to produce large, fertile egg batches for as long as 46 years – with healthy reproductive females as old as 70!
"We're seeing old animals putting out the same number of viable eggs as they did 35 years ago," says Wilkinson. He relates the big female gators to oak trees: "They drop acorns every so often when the weather's right, and then one day they don't, and that's the end of it."
Tom Yawkey purchased this patch of land in the 1920s, and established it as a protected space for wildlife. The site is bordered by ocean to the east, a brackish bay to the north and a river to the south, and is home to a variety of animals, from birds to sea turtles. It also lies at just about the northern limit of the American alligator's distribution.
"The fact that they're on a sanctuary means that the world has to leave them alone," says Wilkinson. "It's like we have a laboratory setup, but it's in the wild." Because the reserve is protected and set aside specifically for scientific research, its resident gators are uniquely unaffected by human activity, remaining "unhunted" for at least a century.
This arrangement has allowed Wilkinson and his colleagues to put together a database of gator info like no other, which forms the basis for many other studies, including research on gator population biology, life history and response to environmental change. This makes the Yawkey Center one of the world's leading sites for answering questions about how best to preserve the American alligator into an uncertain future.
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