A pile of trash on Wake Island provided room and board for invasive rats (photo courtesy CEMML/Jennie Anderson). BY JODI PETERSON
Rats. No, really, rats. These persistent pests, along with other common rodents like mice, infest myriad locations around the world. They gnaw wires, destroy crops, contaminate food, and spread diseases such as plague and leptospirosis. Omnivores with catholic tastes, rats nibble pizza slices in New York subways, munch maize in Tanzanian fields, and nosh on young land crabs on Pacific islands. Thanks to that adaptability and their astonishing reproductive rate, they’re one of the most difficult invasive species to eradicate.
On islands, their presence has been especially harmful. An estimated 90% of the world’s islands have been colonized by invasive rats, mice, or both. The effect on native wildlife has been devastating, as they have no innate defenses against rodents. Rats have destroyed thousands of seabird colonies, eating eggs, nestlings, and even adult birds. While eradication efforts are notoriously challenging, they have proven effective in hundreds of places like Hawadax Island in the Aleutian Islands, Anacapa Island in Channel Islands National Park, the Falkland Islands, and Hawaiʻi’s Lehua Island.
Now, an atoll in the Marshall Islands may soon join that list, thanks to the joint efforts of the U.S. Air Force, U.S. Department of Agriculture Wildlife Services, the nonprofit Island Conservation, Colorado State University’s Center for Environmental Management of Military Lands, and many other partners. Together, they form the Wake Atoll Rat Eradication Project team.
Wake Atoll, the northernmost atoll of the Marshalls, lies about 2,200 miles west of Honolulu. It comprises three coral islands, Peale, Wilkes, and Wake, which is home to an active Air Force installation. The atoll’s lagoon and surrounding waters are managed as the Wake Atoll National Wildlife Refuge and are part of the Pacific Remote Islands Marine National Monument.
In 2020, the WAREP team began a joint project to remove rats from the three islands, using poisoned bait and traps. James Stanford, Center for Environmental Management of Military Lands biosecurity manager, coordinated the eradication effort. Before the removal project began, rats at Wake Island Airfield posed a health hazard, contaminated stored supplies, and ruined residents’ gardens. They impeded military operations by gnawing electrical wiring essential for fighter jets, phones, and Wi-Fi. “The rats outnumbered the humans by at least 1,000 to 1 and would scatter under each step and run over people while they were sleeping,” said Jennie Anderson, the CEMML principal investigator who provides biosecurity and invasive species expertise for the USAF on Hawaii and remote Pacific Islands, including Wake Atoll.
Across the atoll, rats also threatened wildlife, especially imperiled seabirds and shorebirds such as Laysan albatrosses, brown boobies, sooty terns, whimbrels, curlews, and plovers. Fewer birds also meant less guano, which in turn decreased the supply of important nutrients such as nitrogen, both on land and in the surrounding seawater. That deficiency impaired marine life, including corals, gray reef and blacktip sharks, bumphead parrotfish, Napoleon wrasse, threatened green sea turtles, and spinner dolphins.
“Covering an entire atoll, including an active military base, with poison bait and traps while not adversely affecting humans, the military mission, or the environment is a complicated undertaking,” said Stanford. To encourage rats to take bait, other food sources such as trash piles were removed; the eradication team also collected and incinerated kitchen waste from the base daily. Because the poison (brodifacoum, a blood thinner) can unintentionally injure or kill other wildlife, the team monitored fish, aquatic mammal, and bird populations to establish a baseline before spreading bait, then monitored again after baiting. “One of our biggest concerns was ensuring the brodifacoum didn’t get into the water,” said Stanford. “We set up buffer zones around all inland water sources and along the entire coast where we didn’t spread any bait.”
On their days off, the WAREP team tackled other invasive objects on the atoll by volunteering for beach clean-up. Outgoing tides deposit vast amounts of trash on once-pristine beaches. “We removed two shipping containers filled with plastic waste from Wake Island and picked up 3,461 pounds of plastic waste on Peale that were airlifted out via helicopter,” noted Anderson.
Attempts to eradicate the two rat species found on the atoll, Asian house and Pacific (Polynesian) rats, first began in 2012. The Air Force and partners dropped brodifacoum baits, but while Asian house rats have been permanently eliminated, Pacific rats eventually repopulated all three islands. In recent years, another rat species, the white-throated woodrat, native to the southwestern United States, had also become established there.
Elsewhere in the Marshall Islands, other organizations are working on rat eradication as well. In 2023, the Islands’ government led the successful removal of rats from Irooj, a small islet in the chain. Removal operations recently took place on other infested islets; they can’t be declared rat-free, though, until they are monitored a year later to confirm success.
Similarly, ongoing monitoring on Wake Atoll will be necessary to verify that all rats have successfully been eliminated. For a full year, the WAREP team will respond immediately to any sign of rodents by placing additional bait and traps. To head off new incursions, Wake Island Airfield is also implementing stronger biosecurity procedures for arriving ships and planes. The base already uses rodent traps on docks, rodent guards on mooring lines, and similar measures; it will expand those efforts and add others to target potential invasives such as insects, plants, and reptiles.
There’s good reason to be optimistic about the eradication project’s success. Anderson traveled to Wake Atoll in June 2024 to check on the project and sent this email: “I haven’t seen a single live rat. While there are still a few around, the numbers are small and there are high hopes that they will be fully eradicated within one year. This effort is improving the lives of everyone who lives on and visits Wake, and it will also be a big boost to the atoll’s native birds and other wildlife.”