The Conservancy’s Hawai'i and Palmyra Executive Director
A year after all rats were removed from Palmyra Atoll, the island’s unique wildlife is already showing signs of improvement.
The removal effort, which took place in the summer of 2011, involved a ship, 41 humans, two helicopters and 30 rats equipped with radio collars. Island Conservation, the U.S. Fish and Wildlife Service and The Nature Conservancy conducted the operation.
A recently completed survey showed no evidence of rats on Palmyra’s 25 islands. Teams found no rat-chewed coconuts or pandanus seeds, no rat-eaten bird carcasses, no rat tracks and no signs of chewing on peanut butter-flavored detection blocks.
“It is a huge accomplishment for conservation. The program was planned over several years, it was incredibly well researched and very complicated,” said Suzanne Case, executive director of The Nature Conservancy of Hawai`i, which owns Palmyra with the U.S. Fish and Wildlife Service.
Scientists said they are already detecting increased numbers of fiddler crabs, a favorite rat food, as well as new seedling growth for the dominant tree of the Palmyra rainforest, Pisonia grandis. They anticipate that the ecosystem will rebound in the absence of the omnivorous predator, which preys on seabird eggs, seeds, growing plants and an array of other life forms, including crabs.
“It’s too early to tell the impact on birds—on other islands it takes 5 to 10 years to see a measurable effect—but we have seen higher fledgling success on sooty tern colonies. The rats were hitting them pretty hard,” said Alex Wegmann, of Island Conservation, a non-profit focused on protecting island biodiversity.
Rats are fierce predators on islands, and a key goal in island conservation globally has been their removal. In recent years, eradication efforts have succeeded on islands as far removed as South Georgia in the Atlantic, Breaksea Island in New Zealand and Rat Island in the Aleutians. In the Hawaiian archipelago, among the islands from which they have been removed are Mōkapu Island off Moloka`i and Kure and Midway atolls at the far western end of the chain.
“Rats have successfully infiltrated systems and places all around the world. They are predators where predators did not exist. They are very detrimental to seabirds that depend upon these islands for nesting and resting, as well as the invertebrate community. This is putting back the ecosystem closer to the way it’s supposed to be,” said Susan White, USFWS Monuments Superintendent and Refuge Project Leader for the Pacific Reefs National Wildlife Refuge Complex.
The standard method for removal uses a rodenticide, distributed in a way that is least likely to impact birds, crabs and marine animals. On Palmyra, bait was distributed in two sweeps to every known rat habitat, using land-based bait stations, broadcasting from helicopters and delivery into the crowns of coconut trees by slingshot or by a researcher suspended from a helicopter.
Eight weeks after the second sweep, a team found no sign of rats, and a year later, the rats are still absent.
“Although no amount of effort will yield absolute certainty that rodents are absent from Palmyra, the results from this detection effort provide sufficient confidence to say that this is the case for the atoll,” concluded a report on the eradication by Wegmann and Erik Oberg of Island Conservation.
Located 1,000 miles south of Hawaiʻi, Palmyra is a national marine monument, national wildlife refuge and Nature Conservancy preserve. Long recognized as an ideal natural laboratory, the atoll is now a center for scientific study, attracting top researchers from around the world who belong to the Palmyra Atoll Research Consortium.
January 28, 2013