Over countless generations, sea turtles and raccoons achieved a level of equilibrium in their struggles to survive: Turtles laid enough eggs to ensure the future of their species and to allow the occasional meal for land-lubbing raccoons.
Lately, though, the turtles have needed a little help.
"Under natural conditions, sea turtle nests should exist in such concentrations that natural predators like raccoons wouldnt decimate populations," said Bob Warren, a wildlife ecology professor in the UGA Warnell School of Forest Resources. "But human development along the coast has removed so much of the nesting environment that every nest is critical."
How best to help the turtles has been a matter of scientific debate. The National Park Service enlisted Warren and former UGA doctoral student Mary Ratnaswamy to compare methods for achieving the 60 percent sea turtle hatching rate, mandated by its Loggerhead Turtle Recovery Plan, at the Canaveral National Seashore near the Kennedy Space Center in Florida.
Before the UGA study, the Park Service protected nests by covering them with wire screens that contained holes just large enough for hatchlings to emerge. Anchored by steel rods, the screens held the marauding masked bandits at bay. But other coastal wildlife refuges kept raccoons in check through lethal control, capturing and killing the predators.
Both methods have drawbacks, Warren said. Screening is more labor-intensive and costly. During nesting season, people must follow the turtle "crawls" prints made in the sand by crawling turtles locate nests and install protective screens. Lethal control raises obvious questions about ethics, public relations and ecological impact.
"If you remove 30 percent of the raccoons, what effect does that have on the ecosystem? Raccoons also prey on ghost crabs, which eat turtle hatchlings," Warren said. "If youre going to use lethal control, you need to find out the ecological effects."
Warren and Ratnaswamy spent two nesting seasons at the national seashore collecting and analyzing data on three ways to protect turtles nests: screening, lethal control and controlled taste aversion. For taste aversion studies, the researchers spiked chicken eggs instead of rare turtle eggs with an odor-less chemical known to up-set a raccoons stomach and then placed the eggs on the beach where raccoons would find them.
"You hide something in the egg that is tasteless because you want the animal to associate the taste of the egg with the nausea and vomiting," Warren said. "The animal will associate the illness with the egg and will not eat eggs again."
Their study, the first to compare management techniques for turtle nest protection, produced findings that surprised both the researchers and the federal agencies charged with protecting endangered sea turtles. Screening was by far the most effective method at Canaveral National Seashore. And since the Park Service used volunteers, the cost differences were negligible, Warren said.
Nests in the lethal removal and conditioned taste aversion groups were about four times more likely to be destroyed by raccoons.
But findings for Canaveral National Seashore may not hold true for other beaches, Warren said, because of Canaverals unique features: a large raccoon population on a 25-mile long island isolated from nearby forests and other habitats.
"We didnt think the screening method would come out as well because others were having a very high success rate with lethal control," Warren said. "For Canaveral, screening offers the best protection and is the least disruptive to the ecosystem."
For more information, e-mail Bob Warren at firstname.lastname@example.org