At the tip of Hawaii’s northwestern islands lies Kuaihelani – also known as Midway Atoll – a small group of islands that is home to the world’s largest albatrosse colony. More than a million albatrosses they return to Kuaihelani every year to breed. These seemingly pristine islands appear safe, but there is a predator lurking among the seabirds.
House mice (Mus musculus) — the same type that may be in your home — began attacking and killing albatrosses, eating them alive as they land in their nests. I am an ecologist who has been studying the mystery behind these killer rats.
A predator hiding in plain sight
Since the place of intense war during World War IIKuaihelani is now a national wildlife refuge.
With no predators like cats, rats or mongooses, Kuaihelani provides a safe haven for millions of migratory and nesting birds, including mōlī (Phoebastria immutabilis), also known as Laysan Albatrosses. These seabirds, each about the size of a goose, nest in almost exactly the same location every year, producing just one egg a year.
In the 2015 winter nesting season, volunteers and biologists counting birds began seeing horrific, bloody wounds on nesting mōlī. At first, they found only a few mōlī with these mysterious injuries, which included severe chewing along the neck and even scalping. In the weeks that followed, they found dozens of injured mōlī, then hundreds.
Biologists were perplexed. Did a black rat escape from a docked boat? Did a peregrine falcon appear with the last winter storm? Desperate to identify the culprit, biologists installed hunting cameras around mōlī nests.
Cameras captured bizarre nighttime images of rats crawling and chewing on mōlī’s backs and heads. It was the first time a house mouse was observed attacking a live adult, nesting albatross.
Mōlī, like many seabirds, evolved without predators on remote islands. As a result, these seabirds are often strangely fearless and curious – tugging at researchers’ laces or nibbling at our clipboards. This phenomenon is called “island naivety” And as charming as it is, it can spell disaster when non-native predators like rats and cats are introduced to the islands. Lacking innate caution, even the largest seabirds can become helpless prey to predators as small as a mouse.
Developing a taste for meat
During World War II, the islands of Kuaihelani were cleared and covered with war infrastructure. Both black rats and house mice have been inadvertently introduced Right now. Soon, rats began to decimate populations of digging seabirds.
When Kuaihelani’s military importance faded in the 1990s, management of the atoll was transferred to the US Fish and Wildlife Service. The mice were successfully eradicated in 1996, but the rats remained. Considered small and harmless, they did not generate much concern until 2015.
While scientists may never know exactly why rats began attacking and killing mōlī, we have some ideas.
Due to climate change, Kuaihelani has experienced increasingly erratic rainfall, sometimes resulting in long periods of drought or intense rain. During dry periods, vegetation dies quickly. It is likely that the rats’ usual foods, namely seeds and insects, will decrease during these periods. To survive, mice need to find a different source of food.
On an island with millions of birds, seabird carcasses are abundant and attract a rich community of insects, including cockroaches, isopods and larvae. The rats seem to have quite an appetite for these creatures and probably feed on seabird carcasses at the same time. The transition from eliminating dead seabirds to attacking live birds that don’t fight back is just a small step.
As rat attacks on mōlī nests increased from 2015 onwards, it became clear that something needed to be done – and fast. The solution was to get rid of the rats, which, unfortunately, is much easier said than done.
Stubborn rats
Rat eradication is a challenging and risky conservation effort that requires years of careful research and planning. Ideally, rodenticide, a type of poison used to kill rodents, should be offered when rats 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 unique chemical fingerprints of organisms – my colleagues and I were able to discover what organisms did rats eat and in what quantities. We found that rats on Kuaihelani Sand Island eat mainly insects (about 62% of their diet), followed by plants (27%) and finally albatrosses (probably mōlī, about 12%). The Fish and Wildlife Service has identified July as the best time to attempt eradication, as seabird density is typically lowest then.
Due to COVID-19 disruptions, the eradication attempt has been delayed until July 2023, when the nonprofit Island Conservation and the Fish and Wildlife Service meticulously applied rodenticide in several rounds. At first, it seemed to be working. But in the weeks that followed, a few rats were spotted – and then more. In September 2023, eradication was declared unsuccessful.
Some conservationists believe that eradication should be I tried againbut others worry breeding rodenticide-resistant mice. When generations of rodents are repeatedly exposed to rodenticides, they can begin to carry genetic mutations, resulting in poison resistancerendering future eradication efforts ineffective.
Undoubtedly, Kuaihelani’s rats were exposed to the rodenticide a long time ago. When Kuaihelani – or Midway Atoll – was a naval base, rodenticide was likely applied in and around buildings and homes. The eradication of rats in 1996 was another exposure. I am currently researching whether the Kuaihelani rats already have these genetic mutations.
Concerns about rodenticide-resistant rats are not limited to Kuaihelani. Around the world, especially in Europe, there are more and more cases of rodents carrying resistance. Rodents continue to have serious and widespread ecological effects on islands around the world.
For now, I’m focused on helping the mōlī of Kuaihelani survive. But our research can also help inform the growing challenge of resistant mice around the world.
This article was republished from The conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you understand our complex world. It was written by: Wieteke Holthuijzen, University of Tennessee
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Wieteke Holthuijzen has received research funding 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, Knoxville and has collaborated with the U.S. Fish and Wildlife Service and Island Conservation.
