by At the northwest end of the Hawaiian Islands lies Kuaihelani – also known as Midway Atoll – a small chain of islands that is home to the world’s largest albatross colony. More than a million albatrosses return to Kuaihelani each year to breed. These seemingly safe islands look safe, but there is a predator among the seabirds.
house mice (Muscle) — of the same type that may be in your residence — have begun to attack and kill albatrosses, eating them alive while sitting on their nests. I am an ecologist studying the mystery behind these murderous mice.
A predator hiding in plain sight
Kuaihelani became a national wildlife sanctuary during the intense fighting during the Second World War.
With no predators such as cats, rats or mongooses, Kuaihelani provides a safe haven for millions of nesting and migratory birds, including mōlī (Phoebastria immutabilis), also known as the Laysan albatross. These seabirds, about the size of a goose, nest almost the same every year, and produce only one egg a year.
In the winter nesting season of 2015, bird-counting volunteers and biologists began seeing gruesome, bloody wounds on mōlī nests. At first, they only found a few mōlī with these mysterious injuries, including severe chewing along the neck and even scalping. In the following weeks, they found dozens of injured mōlī, then hundreds.
Biologists were stumped. Did a black rat escape from a docked boat? Did the peregrine falcon blow away with the latest winter storm? Desperate to identify the culprit, biologists set up game cameras around the mōlī nest.
The cameras captured strange footage during the night of mice crawling and chewing on the backs and heads of moles. This was the first time a house mouse had ever been seen attacking a live adult, nestling albatross.
Mōlī, like many seabirds, have evolved without predators on remote islands. As a result, such seabirds are often scary and curious – tugging at researchers’ shoe lights or nibbling on our cutting boards. This phenomenon is called “naiveté island” and, as nice as it is, it can be disastrous when non-native predators such as rats and cats are introduced to the islands. Without innate warning, even the largest seabirds can become defenseless prey to predators as small as a mouse.
Developing a taste for meat
During World War II, the Kuaihelani islands were cleared and covered with wartime infrastructure. Black rats and house mice were inadvertently introduced at this time. Soon, the rats began to decimate the number of shorebirds.
When Kuaihelani’s military importance declined in the 1990s, management of the atoll was transferred to the US Fish and Wildlife Service. Rats were successfully exterminated in 1996, but mice remained. Thought to be small and harmless, they were not much of a concern until 2015.
Although scientists may not know exactly why mice started attacking and killing mōlī, we have some ideas.
Due to climate change, Kuaihelani has occasionally experienced increasing neglect, sometimes resulting in long dry spells or heavy rainfall. During dry periods, vegetation dies back quickly. The usual food items for mice, namely seeds and bugs, are likely to decline during these periods. To survive, mice must find another food source.
On an island home to millions of birds, seabird carcasses are abundant and attract a rich community of bugs, including cockroaches, isopods and maggots. Mice seem to have a fondness for these critters and probably eat seabird carcasses at the same time. The transition from scavenging dead seabirds to attacking live birds that don’t fight back is just a small step.
As mouse attacks on nesting moles increased from 2015 onwards, it was clear that something needed to be done – and fast. The solution was to get rid of the mice, which, unfortunately, is much easier said than done.
die-hard mice
Eliminating mice is a challenging and dangerous conservation effort that requires years of research and careful planning. Ideally, rodenticide, a type of poison used to kill rodents, should be offered when mice are most hungry and likely to eat it. This requires knowing exactly what they are eating and when those food sources are scarce.
By extracting and sequencing DNA from the mouse droppings and performing stable isotope analysis – a technique that identifies the unique chemical fingerprints of organisms – my colleagues and I could work out which organisms the mice were eating and which ones. amounts. We found that mice on Sand Island of Kuaihelani mainly eat bugs (about 62% of their diet), followed by plants (27%) and finally albatross (probably mōlī, about 12%) . The Fish and Wildlife Service has identified July as the best time for the eradication effort, as seabird densities tend to be lower then.
Due to the outbreak of COVID-19, the eradication effort was delayed until July 2023, when the non-profit organization Island Conservation and the Fish and Wildlife Service carefully applied rodenticide in multiple rounds. At first, it seemed to work. But in the following weeks, a few mice were seen – then more. By September 2023, eradication was declared unsuccessful.
Some conservationists believe eradication should be attempted again, but others worry about creating rodenticide-resistant mice. When generations of rodents are repeatedly exposed to rodenticide, they can develop genetic mutations that can carry resistance to the poison, rendering future eradication efforts ineffective.
No doubt, mice on Kuaihelani have been exposed to rodents for a long time already. When Kuaihelani – or Midway Atoll – was a naval base, it is likely that rodents were introduced into and around buildings and residences. Another revelation was the extermination of the rats in 1996. I am currently researching whether mice on Kuaihelani already have these genetic mutations.
The concern about rodenticide-resistant mice is not limited to Kuaihelani. All over the world, especially in Europe, there are more and more cases of rodents carrying resistance. Rodents continue to have severe and widespread ecological consequences on islands around the world.
For now, I am focused on helping mōlī Kuaihelani survive. But our research may also help inform the growing challenge of resistant mice around the world.
This article is republished from The Conversation, a non-profit, independent news organization that brings you facts and analysis to help you make sense of our complex world.
It was written by: Wieteke Holthuijzen, University of Tennessee.
Read more:
Wieteke Holthuijzen received funding for 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, Knoxville and has collaborated with the US Fish and Wildlife Service and Conservation Islands.
