Its a bit early to declare Palmyra Atoll National Wildlife Refuges intensive, monthlong rat eradication program a success. True, no ones seen hide or hair of a rodent on the remote Pacific island chain since the $2.7 million project was completed last summer. But the infestation was severethe nonnative rats had no natural predators, foraged for food in broad daylight and looked humans calmly in the eye. And in a tropical climate, its accepted that you must be rodentfree for at least a year before proclaiming victory.
Its an allornothing thing, says refuge manager Amanda Meyer. Theres no we almost eradicated rats. You eradicate them or you fail.
Still, you can hear her excitement as she talks about changes that have been observed on the refuge since the eradication.
Purple fiddler crabs wandering beaches in record numbers. Green pisonia seedlings carpeting the ground. Population explosions of dragonflies and crickets. Thousands of sooty tern fledglings, compared with a couple of hundred in previous years.
Restoring Palmyra Atoll to its natural state has been a priority for the refuge since its 2005 establishment. The refuge comanages the atoll with The Nature Conservancy. Another nonprofit, Island Conservation, spearheads invasive species research.
Palmyra Atoll is a U.S. territory between Hawaii and American Samoa. Its a critical stopover point for migratory shorebirds and seabirds and is home to many rare, threatened and endangered species, including bristlethigh curlew, green and hawksbill sea turtles, and the worlds largest land invertebrate, the coconut crab. With more than 175 inches of rain a year, it supports one of the Pacifics last remaining tropical coastal strand forests. Its miles of coral reefs are among the most diverse on Earth.
But what makes Palmyra especially valuable is that it has never been permanently inhabited by humans. As the only undeveloped forested atoll remaining in the U.S. tropical Pacific, it is an endangered ecotype, says Alex Wegmann, who directed the rat eradication project for Island Conservation. Its the only wet tropical island in that region that has a natural future ahead of it.
When its not being besieged by rodents, that is. The rats, likely introduced by American troops in World War II, had the run of the islands for 70 years, reproducing rapidly in the warm climate. It was a rats paradise, says refuge supervisory biologist Beth Flint. Youd see them in the forest, leaping about, unconcerned with humans. They had beautiful weather, lots of food. Theyd eat the seabirds eggs as fast as the birds could lay them.
Scientists have made great strides in recent years in ridding tropical islands of rodents, Flint says, but Palmyras moist, dense environment presented particular challenges: What kind of bait would work when wet? How do you place the bait in overhanging palm trees without contaminating the water below? How do you keep shorebirds from ingesting the bait?
After seven years of study and some test runs, the rat team settled on the toxicant (brodifacoum), the amount of bait (four times as much as is common on arid, temperate islands, because of the complex ecosystem) and a multipronged approach to dispersing it, including aerial broadcast via helicopter, hand placement at meticulously plotted GPS points, and slingshotting it into 4,000 trees.
To minimize the incidental take of shorebirds, the team timed the project for boreal summer, when the birds return to the Arctic to breed. Of the remaining birds, an effort was made to capture, care for and release them back into the wild.
The Palmyra Atoll project is in the monitoring phase, with all signs indicating that the rats are truly gone. Meanwhile, the fight goes on. Rat eradication, also funded through the Refuge Systems invasive species program, is scheduled this year at Puerto Ricos Desecheo National Wildlife Refuge. If the Caribbean island refuge needs any tips, theres an atoll in the central Pacific with some good stories to share.
K. C. Summers is a Virginiabased freelance writer and editor.