At the tip of the northwestern Hawaiian Islands lies Kuaihelani, also known as Midway Atoll, a small cluster of islands that are home to the world’s largest albatross colony. More than a million albatrosses return to Kuaihelani to breed each year. These seemingly pristine islands appear safe, but there’s a predator lurking among the seabirds.
House mice (mus musculus) They began attacking and killing albatrosses – the kind you might have in your home – and eating them alive while they sat in their nests. I’m an ecologist investigating the mystery behind these killer mice.
A predator hiding in plain sight
Once upon a time II. Kuaihalani, the site of intense fighting during World War II, is now a national wildlife refuge.
Free of predators such as cats, rats or mongooses, Kuaihalani provides a safe haven for millions of nesting and migratory birds, including mōlī (Phoebastria immutabilis), also known as Laysan albatrosses. These seabirds, each about the size of a goose, nest in almost the same spot every year and produce only one egg per year.
During the winter nesting season of 2015, bird counting volunteers and biologists began seeing horrific bloody wounds on nesting mōlī. At first, they found only a few molīs with these mysterious injuries, which included violent chewing along the neck and even scalping. In the weeks that followed, they found dozens, then hundreds, of injured mōlī.
Biologists were stunned. Had a black mouse escaped from a docked boat? Did a peregrine falcon fly by during the last winter storm? Desperate to identify the culprit, biologists set up game cameras around the mōlī’s nest.
Cameras captured strange nighttime images of mice crawling and chewing on mōlī’s backs and heads. This is the first time a house mouse has been observed attacking a live adult albatross while it was nesting.
Like many seabirds, Mōlī evolved without predators on remote islands. As a result, such seabirds are often strangely unafraid and curious; He pulls researchers’ shoelaces or gnaws at our notebooks. This phenomenon is called “island naiveté,” and no matter how attractive, it can spell disaster when non-native predators such as rats and cats are introduced to islands. Due to their innate lack of attention, even the largest seabirds can become defenseless prey for predators as small as mice.
Improve meat taste
During World War II, the Kuaihelani islands were cleared and covered with wartime infrastructure. Both black mice and house mice were accidentally introduced during this period. Soon the rats began decimating the population of burrowing seabirds.
When Kuaihelani’s military importance declined in the 1990s, management of the atoll was turned over to the U.S. Fish and Wildlife Service. Rats were successfully eradicated in 1996, but rats remained. Although they were thought to be small and harmless, they did not cause much concern until 2015.
Although scientists don’t know exactly why the mice started attacking and killing mōlī, we have some ideas.
Due to climate change, Kuaihelani is experiencing increasingly erratic rainfall, sometimes resulting in long periods of drought or heavy downpours. During dry periods, vegetation dies quickly. Seeds and insects, the usual food items for mice, are likely to decrease during these periods. Mice need to find a different food source to survive.
On an island with millions of birds, seabird carcasses are abundant and attract a rich community of insects, including cockroaches, isopods and maggots. The mice seem to have quite an appetite for these creatures, and they probably also feed on seabird carcasses. It’s only a small step from destroying dead seabirds to attacking creatures that don’t fight back.
As mouse attacks on nesting mōlī increased from 2015 onwards, it was clear that something had to be done quickly. The solution was to get rid of the mice, which unfortunately is much easier said than done.
deadly mice
Eradicating mice is a challenging and risky conservation effort that requires years of research and careful planning. Ideally, rodenticide, a type of poison used to kill rodents, should be offered when the mice are hungriest and most likely to eat it. This requires knowing exactly what they eat and when those food sources are scarce.
By extracting and sequencing DNA from mouse poop and analyzing stable isotopes, a technique that identifies organisms’ unique chemical fingerprints, my colleagues and I were able to understand which organisms the mice were eating and in what quantities. We found that mice on Kuaihalani’s Sand Island eat mostly insects (about 62% of their diet), followed by plants (27%), and finally albatross (probably mōlī, about 12%). The Fish and Wildlife Service has identified July, when seabird densities are generally lowest, as the best time to attempt eradication.
Due to COVID-19 setbacks, the eradication effort was delayed until July 2023, when the Island Conservancy and the Fish and Wildlife Service, a nonprofit organization, meticulously applied rodenticide in multiple rounds. It seemed to work at first. However, few mice were seen in the following weeks; even more. As of September 2023, the elimination process has been declared unsuccessful.
Some conservation practitioners believe eradication should be tried again, but others worry about creating mice resistant to rodenticides. When generations of rodents are repeatedly exposed to rodenticide, they may begin to carry genetic mutations that result in resistance to the poison, rendering future eradication efforts ineffective.
Undoubtedly, rats at Kuaihelani have already been exposed to rodenticides for a long time. While Kuaihelani, or Midway Atoll, was a naval base, rodenticides were applied in and around buildings and residences. The extermination of rats in 1996 was another exposure. I am currently investigating whether mice from Kuaihelani have these genetic mutations.
Concerns about rodenticide-resistant mice are not limited to Kuaihalani. The number of cases of resistant rodents is increasing worldwide, especially in Europe. Rodents continue to have serious and widespread ecological impacts on islands around the world.
For now, I’m focused on helping the mōlī in Kuaihalani survive. But our research may also help inform the growing fight against resistant mice worldwide.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Wieteke Holthuijzen, University of Tennessee.
Read more:
Wieteke Holthuijzen received funding for the research from the National Science Foundation Graduate Research Fellowship Program, Northern Illinois University, Sigma Xi, and Island Conservation. She is affiliated with the University of Tennessee at Knoxville and has collaborated with the U.S. Fish and Wildlife Service and the Island Conservancy.