Marsh shrew

The marsh shrew (Sorex bendirii), also known as the Pacific water shrew, Bendire's water shrew, Bendire's shrew and Jesus shrew, is the largest North American member of the genus Sorex (long-tailed shrews). It is primarily covered in dark-brown fur and lives near water along the Pacific coast from southern British Columbia to northern California. This small animal can run on top of the water for a few seconds because it traps air in its fur to stay buoyant.

Marsh shrews measure about 16 cm (6.3 in) long, including a tail that is about 7 centimetres (2.8 in). They weigh, on average, between 14.5 and 16 grams (0.51 to 0.56 ounces). These shrews hunt tiny animals, called invertebrates, both on land and in the water.

Unfortunately, marsh shrews are rare today. Their numbers are thought to be getting smaller, and in some places they are considered to be in danger of disappearing completely.

Description

Skull top and bottom views

The marsh shrew is the largest member of the Sorex group in North America. It has dark brown fur and a long tail. Some groups on the Olympic Peninsula may have white fur on their belly. It is about 16 cm long, including a 7-centimetre tail, and weighs between 14.5 and 16 grams. Its hind feet have coarse hairs on the toes.

The marsh shrew is larger than most other shrews in its area, except for the American water shrew. It has a longer snout and more distinct fringed hairs on its fur compared to the American water shrew. Its skull is large with a special curve along the front. The marsh shrew’s teeth have a unique pattern and reddish coloring from iron, which helps strengthen them.

Taxonomy and naming

The marsh shrew was first described in 1884 by Clinton Hart Merriam. He named it Bendire's shrew after Charles Bendire, an ornithologist who helped Merriam. Merriam thought it was a new kind of shrew and put it in a new group called Atophyrax. Later, scientists moved it to the group Sorex, which it shares with the American water shrew.

The marsh shrew lives in a smaller area along the northwest coast, while the American water shrew is found more widely across western mountains and even into Canada and the eastern U.S. Scientists have studied how these shrews are related and found that they belong to the same subgroup, Otisorex.

The marsh shrew has three subspecies:

• S. bendirii albiventer
• S. bendirii bendirii
• S. bendirii palmeri

These subspecies live in different places: the Olympic Peninsula of Washington, the Cascades and southwestern British Columbia, and coastal Oregon, respectively.

Distribution and habitat

The marsh shrew lives near water in places like marshes along the Pacific coast, from southern British Columbia through Washington, Oregon, and into northwestern California. These shrews like wet areas with lots of plants and trees for cover. They can be found from sea level up to about 4,356 feet in places like the Cascades. In British Columbia, they are considered one of the rarest small animals there. Studies in Oregon show they are usually found close to streams in forests of different ages.

Behavior and ecology

The marsh shrew eats small animals like spiders, earthworms, and centipedes, both on land and in water. It can swim and dive to catch food underwater using its whiskers and lips. It can run on top of the water for a few seconds because air trapped in its fur keeps it floating.

These shrews are active mostly at night and have a short life of about 18 months. Females have about three or four babies after a three-week pregnancy. They build nests from bark in tunnels or under logs. Although they can smell strongly, they do not see well and may run off edges without noticing.

Human interaction

Before Donald Pattie's research in the late 1960s, not much was known about marsh shrews. Most of what people knew came from notes about where they live and how to catch them. Scientists learned more when they studied these shrews in captivity.

Marsh shrews are considered "Endangered" in Canada by the Committee on the Status of Endangered Wildlife in Canada. Their homes in British Columbia, especially the lower Fraser Valley, are getting smaller because of development. While they are rare and their numbers are going down, they are not in immediate danger according to the IUCN. This is because their decline is not happening fast enough to put them in a more serious category. Wetlands where they live are disappearing mainly due to cities growing and land being used for farming.