Vampire Mice II: Mice changing diet, growing bigger as they attack giant seabirds

 Laysan albatross with mouse injury. Credit: USFWS.

Like characters in some horror movie, house mice are moving up the food chain and getting bigger.

They’re feeding on chicks and now adult seabirds, leaving hundreds of three-foot-tall albatrosses bleeding from their necks, heads and backs, like victims in a vampire flick.

In one case, they are also changing in size—nearly doubling in mass on one Atlantic island where they aggressively eat seabird chicks.

The lowly mouse, Mus musculus, has always been an omnivore, but they’ve never had the reputation of rats as attack rodents. That is changing on islands around the world.

The latest spooky change in their level of aggression came on  a remote Hawaiian Island: Sand Island at Midway Atoll at the remote western end of the Papahānaumokuākea Marine National Monument, which takes up all of the Northwestern Hawaiian Islands and considerable square mileage of the surrounding waters.

On Midway, mice are biting the necks of adult Laysan albatross, chewing down skin and fat and muscle, and drinking blood.  Hundreds of the big birds have been found dead, and more hundreds of abandoned nests suggest other injured parent birds may have died at sea.

Night video of the nesting areas show the tiny gray mice climbing the backs and necks of the albatrosses, repeatedly sipping at gaping wounds they have chewed into the birds’ bodies.

Mice going after big adult birds at Midway started out of the blue in 2015, and this was new. This was another step, something not seen before anywhere. Wildlife officials are now studying ways to wipe out the mouse population, before the predation gets worse.

We wrote about this at Raising Islands here. 

Efforts to control predation on important seabird nesting islands has previously mainly focused on rats—mainly Pacific rats and black rats, which are also known as roof rats and ship rats. But in the past two decades, mice have stepped up as serious predators of seabirds.

Mice have been caught attacking soft chicks and eggs on bird nesting islands for some time. Here is a Live Science piece on attacks at other islands. 

On Gough Island in the South Atlantic, game cameras recorded swarms of mice attacking nestlings of Tristan albatross (Diomedia dabbenena,) great puffins (Puffinus gravis) and Atlantic petrel (Pterodoma incerta.)

“One video showed up to 10 mice mauling an albatross chick and eating from three open wounds on its body,” wrote Live Science writer Jeanna Byer in 2007.

Puffins and petrels are smaller seabirds, the size of mynah birds or pigeons. Albatrosses, which can be three feet tall with wingspans of six to 11 feet, are huge.  A mouse standing up might reach four inches in height. In climbing an albatross, they are climbing a bird nine times taller than they are.

The authors of a 2012 scientific paper in Animal Conservation on that situation wrote: “mice cannot be ignored as a potential threat to island fauna, and island restoration and management plans should routinely include eradication of introduced mice.” 

Injured albatross at Midway in colony. Credit; USFWS.

A 2016 piece in Smithsonian suggests that mice, fed on a rich diet of seabird flesh, are actually changing in size—getting huge. 

They are nearly twice the weight of standard house mice. The standard house mouse is tiny, weighing only about 16 to 25 grams. On Gough, the average mouse runs more than 35 grams.

“They’re the largest and heaviest mice anywhere in the world,” said Richard Cuthbert of the Wildlife Conservation Society.

Cuthbert was the lead author of a 2016  Journal of Mammalogy  article that suggested that the bird diet is a primary cause of the change in mouse size. 

Of course it is not only adult birds that mice attack when they get established on islands. 

Wildlife officials in New Zealand have noted mice killing not only seabird chicks but native lizards, seedlings and bird eggs. New Zealand has removed rats and mice from several offshore islands.

© Jan TenBruggencate 2018