Try, try again . . .

The U. S. Department of Agriculture Wildlife Services recently announced that it is partnering with Parallel Flight Technologies to develop and test a drone-based system for aerial delivery of rat poison on Wake Island. Wake’s last rat eradication program took place in May 2012 and, during my visit there six months prior, preparations were well underway as authorities mapped bait stations and helicopter distribution routes and adopted strict garbage protocols. Meanwhile the little rats scurried about, oblivious to their impending destruction. At the end of the 2012 eradication program, enough rats survived to regroup, revive, and repopulate Wake Island.

Setting aside the fact that humans are arguably the most invasive species on the planet, rats have a marked ability to adapt quickly to foreign environments and exploit diverse food sources. Rats native to Southeast Asia hitchhiked their way across the Pacific Ocean with seafarers who fanned out over many miles and generations to settle the islands. The Spanish explorer Alvaro de Mandana, who made the first recorded sighting of Wake in 1568, observed the surface swarming with hopping rats, which indicates that Polynesians or other islanders had (probably inadvertently) introduced rodents to the atoll long before. With no source of fresh water on the island the people left, but the rats stayed for Wake’s unlimited omnivore banquet of vegetation, insects, seabird eggs and chicks. Two species of rat that colonized Wake were later identified as the Polynesian Rat, aka Pacific Rat or Little Rat, (Rattus exulans) and the Asian House Rat (Rattus tanesumi).

Wake’s modern rat eradication efforts are justified by preservation of bird species, but rats have rattled the island’s human inhabitants since they first came to stay on the atoll in 1935. With the initiation of Pan American Clipper operations, staff offered overnight passengers air rifles for evening rat-shooting excursions. This entertaining pastime developed many iterations over the decades as new residents and visitors introduced a variety of weapons, prizes, bagging and bragging rights. Meanwhile the rats ran for cover, copulated, and carried on eating.

Wake Island was utterly devastated by the Second World War, but the vegetation revived, rats emerged, and seabirds returned. As the postwar population on Wake expanded in the 1950s and 60s, residents often brought along cats as pets and “mousers.” As the cats flourished and reproduced, some escaped domesticity, became feral, and preyed on seabirds and their young – as well as the nimble little rats. When FAA administration of the island ended in the 1970s and families left the island the feral cat population exploded (and the rat population plummeted) raising concerns about endangered nesting seabirds.

By the 1990s feral cat predation had reached a crisis point on Wake. In a 2008 bulletin issued by the Smithsonian Institution Mark J. Rauzon gives a full accounting of the cat eradication program on Wake. Between 1996 and 2002 some two hundred cats were eliminated by trapping and hunting. In the summer of 2003 a concentrated program killed another 170 feral cats over six months. In the coming years only two cats were sighted, but there was no evidence of reproduction. Nesting seabird counts rose dramatically – and the rat population also rebounded with gusto. . . which prompted the rat eradication program of 2012.

Lengthy studies can be found online that evaluate and critique the partially successful 2012 program, what went wrong, and how to fix it on the next try. While the Asian House rat was completely eradicated in the program, resilient little Polynesian Rat survivors who did not consume a lethal dose of the bait quickly repopulated Wake. Problems included failure to account for breeding cycles, bait stations that allowed competitor access (turns out hermit crabs like the bait and are not harmed by it), large exclusion zones at the airfield, incomplete knowledge of underground infrastructure, and uneven aerial application by helicopter.

Cue the drones! The Parallel Flight Technologies press release points out that the high levels of biodiversity and evolutionary uniqueness on islands makes them vulnerable to species extinction by invasive species. Eradication programs promote restoration, resilience, and return to thriving ecosystems. The company’s new drone bait delivery technology may be a game changer, but the Wake rats have found ways to survive typhoons, shooting parties, world war, traps, and cats. Bring it on.

Pacific rat, NZ Dept. of Conservation, ref #10033848, photo by Dick Veitch