Current Nature: Small But Mighty Mice

Unlike the mainland, Nantucket has a very limited roster of mammals. We lack New England mainstays such as coyotes, raccoons, and skunks, and although some animals, such as White-tailed Deer are ubiquitous on-island, in general, the mammal diversity is much lower than elsewhere.

The one exception is with small mammals. Some research has been done locally on these species, including population monitoring by the Nantucket Conservation Foundation at Head of the Plains. Through monitoring and anecdotal observations, it is clear that mice, moles, voles, and shrews thrive in Nantucket’s grasslands and heathlands. Most of the year, these critters are secretive and hard to find, but as winter approaches, this starts to change. To survive the winter, animals such as mice travel far and wide to search for food. Unfortunately, they sometimes venture into human spaces such as homes, cars, and garages, which can create conflict.

The most populous small mammal on-island is the White-footed Mouse. This native rodent is an important prey source for many species, but it is also a significant host for ticks and a vector of tick-borne illnesses. They have evolved to have a short lifespan with many offspring, and population sizes can vary greatly from year to year. On Nantucket, estimates have indicated that in a boom year, there may be over one million White-footed Mice on the landscape, and in bust years, as ‘few’ as 250,000. Either way, that is still a lot of mice! An interesting effort ongoing by MIT scientists, known as Mice Against Ticks, aims to breed and release mice on-island that are immune to Lyme disease. The goal would be to stop the cycle of disease transmission on Nantucket, although this effort is still in the very early stages and would need community buy-in, landowner permissions, and other permits to proceed.

White-footed mice are the preferred prey of Northern Harriers, which are raptors. Although the Northern Harrier population is on the Threatened list in Massachusetts, they thrive on Nantucket. This is largely due to the abundance of rodents, the absence of mammalian predators, and the availability of large grassland habitats necessary for nesting. Mice are also often eaten by Barn Owls and Red-tailed Hawks. If you care about these majestic birds, one way you can help is by not using rodenticides. When a mouse ingests rodenticide, the poison bioaccumulates in the body and can travel up the food web. If a raptor ingests the poisoned mouse, it will subsequently die. In cases where you are dealing with a mouse problem, there are methods such as traps or deterrents that will eliminate rodents without causing unintended impacts on other species.

In addition to White-footed Mice, Nantucket is also home to the Meadow Jumping Mouse. These petite critters have enlarged hind feet, which allow them to take large leaps, much like a tiny kangaroo. When alarmed, these leaps can measure up to three feet! That is more than four times their body length. They are also excellent diggers and decent swimmers. They tend to thrive in areas of high humidity, such as grassy meadows, but they are harder to find than other rodents on the island.

Some small mammals are found only on specific islands. The tiny island of Muskeget, near Tuckernuck, is home to a unique vole known as the Muskeget Vole. This small rodent is not only exclusive to Muskeget but is also Massachusetts' only endemic vertebrate species, meaning it exists nowhere else in the world.

The last confirmed sighting of a Muskeget vole was in 2015, which raised concerns about its status. However, in August 2022, researchers Skyler Kardell and Lily Morello made an exciting discovery—they successfully trapped and confirmed that the species is still alive and thriving on Muskeget. This finding underscores the importance of protecting all small mammals, no matter their size.

Due to their small size, ability to burrow, and nocturnal tendencies, we often do not get to see rodents up close. Even though they may not be as charismatic as large mammals, it is important to remember the role these species play in our ecosystems. Without mice and other rodents, food webs would collapse. So next time you see a hawk or owl soaring through the sky, you can thank a mouse for that!

Stay tuned for more editions of Current Nature, a bi-weekly column featuring seasonal topics, natural history information, and advice on the outdoors from the staff at the Linda Loring Nature Foundation.