DEPARTMENT OF LAND AND NATURAL RESOURCES
LAURA H. THIELEN, CHAIRPERSON
Phone: (808) 587-0401
Fax: (808) 587-0390
For Immediate Release:
Rat Eradication Proposed On Mokapu Island, Moloka'i
U.S. FISH AND WILDLIFE SERVICE
KAUNAKAKAI, HAWAI‘I — A rat eradication project proposed to protect and restore wildlife habitat on Mōkapu Island will be explained to the public during two upcoming public meetings on Moloka‘i in early January. This ten-acre island off the north coast of Moloka‘i is home to three nesting seabird species and an incredible 29 species of native plants, 17 of which are only found in Hawai‘i.
The meetings are sponsored by the U.S. Fish and Wildlife Service and the Department of Land and Natural Resources and will be held on Thursday, January 3, 6 p.m. at Kilohana Community Center, and Friday, January 4, 6 p.m.. at Mitchell Pau‘ole Community Center.
At least three seabird species—wedge-tailed shearwaters (‘ua‘u kani), red tailed tropicbirds (koa‘e ‘ula), and white-tailed tropicbirds (koa‘e kea) nest on the island. Mōkapu also has 11 of the last 14 Pittosporum halophilum (hō‘awa) plants in the wild and a small population of loulu lelo (Pritchardia hillebrandi) palms, which are becoming increasingly rare. The top threat to these island inhabitants is the rat.
“Mōkapu contains some of best remaining native coastal habitat in the state,” Fern Duvall, Wildlife Biologist for the Hawai‘i Department of Land and Natural Resources, Division of Forestry and Wildlife. “The planned eradication efforts are designed to protect the island’s plant and wildlife from rat infestation.”
Nearby Huelo Island, which does not have rats (which are known to eat loulu seeds), is thickly covered with these palms and is the last coastal palm forest in the state, with the exception of Nihoa Island in the Northwestern Hawaiian Islands. Fossil evidence indicates that loulu palm forests once covered huge areas of coastal lowlands throughout the main islands in Hawai‘i.
“Rats are currently eating these native plants, seabird eggs and chicks, but Mōkapu could be a safe haven for these and other rare species if rats are eradicated,” said Chris Swenson, Pacific Islands Coastal Program Coordinator for the U.S. Fish and Wildlife Service. “Since the early 1990s, 57 islands worldwide have been cleared of rats using a similar method of aerial bait distribution that we are planning for Mōkapu.”
After ridding rats from islands elsewhere, bird populations have been known to double or quadruple in size, where tens of chicks might have survived to fledge, now hundreds survive, according to Swenson. Thousands of seedlings of plants come up in the absence of suppression by rats. “The removal of rats is fully expected to create a secure refuge and spectacularly successful breeding ground for native birds, insects and plants,” he said.
To control the rats, bait pellets containing 50 parts per million (0.005%) of the rodenticide diphacinone would be evenly deposited on Mōkapu by using a bait spreader carried under a helicopter. The pellets are about the size of a dog kibble.
Diphacinone was chosen because it was originally developed and used as a human heart medication (marketed as Dipaxin). Diphacinone was prescribed for many years as a blood thinner (anti-coagulant) in heart patients, but use of this drug was discontinued because more effective anti-coagulants were found (including Heparin and Coumadin).
In field trials in native forests in Hawai‘i, rats were by far the main animal eating the placebo baits and native birds in the area were not attracted to it. In order for the rodenticide to be effective, each rat must be able to find enough bait within its own territory over a period of several days to amount to a lethal dose. Past studies demonstrate it is critical that bait get evenly distributed over the entire island into every rat territory, at a rate of about 1 pellet per square meter. The helicopter pilot will control the application and track where the pellets have already been spread to ensure that all sides of the steep island receive the bait. Initially, bait would be applied two times, with about 5-7 days between applications.
Based on Hawai‘i lab studies and field trials with diphacinone bait, biologists fully expect that rats would be eradicated from Mōkapu with two applications of diphacinone. Biologists will continue monitoring for rats and determine if additional applications of bait pellets are needed.
A demonstration using placebo bait pellets on Mōkapu will occur sometime during the first 10 days of January, with the exact date to be determined by weather conditions. Limited space is available for public observation.
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For more information, contact:
U.S. Fish and Wildlife Service
Department of Land and Natural Resources