In 1780, a Japanese ship ran aground on the Aleutian island Howadax (pronounced “How-a-tha”, meaning “welcome”). Earlier this year, scientists visiting the island discovered the carcasses of 43 bald eagles and 213 glaucous-winged gulls on the island. The story of Rat Island is both a cautionary tale and a story of redemption gone awry.
After rats invaded the island from the grounded ship nearly 250 years ago, they quickly reproduced to staggering levels and ate their way through the entire populations of native puffins, petrels, auklets, and many others. With no native mammal predators, the rats soon became the only notable feature of the island, and it earned its new name in the early 1800s.
The story is a familiar one. According to Island Conservation, rats are to blame for 40-60% of all seabird and reptile extinctions, with 90% of those occurring on islands. In 2007, Alaskan and federal wildlife biologists tried to reclaim the island from the rat populations. They laced grain cakes with the blood thinner brodifacoum, and conducted trials. In the trials, 88% of the rats died in their burrows, posing no risk to scavenging bird species. They concluded “some bald eagles may be exposed to brodifacoum residues but are unlikely to die.” The large scale restoration project occurred last September, when a helicopter dropped the poisoned grain cakes in a grid pattern over the entire 10 square mile island. Immediately after the poison drop, workers removed any rodent carcasses.
In June, a two-week intensive survey of the island was conducted. Field workers saw no sign of invasive rat populations, and observed several nesting bird species on the island, including Aleutian cackling geese, ptarmigan, peregrine falcons, and black oystercatchers. They also discovered the carcasses of over 200 gulls and bald eagles in various stages of decomposition.
After taking samples and testing the carcasses, all of the birds were confirmed to have been poisoned by brodifacoum, and USFWS is conducting an investigation into the restoration’s protocol. They theorize that some gulls may have consumed the poison, and that the eagles then ate the dead gulls. Since an estimated 90% of islands are now infested with rats, scientists have a strong motivation to perfect the process of eradication with low mortalities of native species. While Alaska has a healthy population of bald eagles, with 2,500 in the Aleutians alone, and 50,000 in the rest of the state, other smaller rat-infested islands don’t have those sort of stocks to draw upon. For now, Rat Island will be carefully monitored over the next couple of years for any signs of a rat rebound, before eventually re-adopting it’s original Aleutian name.