Yes, they exist, and they may drive some seabirds straight to extinction. Researchers on Gough Island, way down in the southern Atlantic about half way between South America and Africa, have been studying the impacts of house mice on Atlantic Petrels. The petrels have been breeding on Gough Island for millennia, while the house mice are a more recent introduction brought there by, guess who? Yep, humans with boats. Since they were inadvertently dropped off on Gough, the mice have evolved much larger size than the average mouse gnawing a hole in your cereal boxes. The mice on Gough are now about ten inches long, not including the tail. This trend toward larger size is typical of small mammals marooned on islands over generations, and consistent with theories of island biogeography known as “The Island Rule”first posited by J. Bristol Foster in the 1960s.
Now, these monster mice have multiplied as rodents are wont to do, and when their more typical sources of food run low, they turn to a massive, fleshy buffet: the large, immobile chicks of the Atlantic Petrel sitting in their underground burrows with no evolutionary defenses against the new comer mice. The mice simply eat the helpless chicks alive while the parents are out foraging.
The impacts are not slight–a study in Animal Conservation shows that millions of the chicks are being killed and eaten by mice every year, and a majority of their mathematical models project that the species will be driven into endangered, “Red List”status. Based on these numbers, an outcry is now rising for the extermination of the giant carnivorous mice. Gough is not the first nor the only island with a rodent problem, and all over the world, various strategies have been used to deal with invasive species. Poison is the most likely tactic to be used on Gough, and of course, it’s not without peril to non-target species, but with an infestation of this size and severity, there are few alternatives. It’s a problem of human making, and humans, being imperfect ourselves, have but imperfect means of fixing it. We’ll be rooting for the helpless, burrow-dwelling petrels and hoping the species itself won’t meet its end staring into the beady, heartless eyes of gigantic mice.