Northern Short-tailed Shrew

Blarina brevicauda
Saturday, July 17, 2010

The Northern Short-tailed Shrew’s name, brevicauda, means literally “brief (brevi) tail (cauda).” These deceptively ordinary little creatures hold a claim as one of the very few venomous mammals, use echolocation to augment their weak eyesight, and can capture prey as large as small birds.

Northern Short-tailed Shrews are small rodents with velvety fur that is typically slate gray, dark, or brownish on their dorsal side, and only slightly paler on their ventral. Their bodies are 7.5-10.5 cm long, with tails up to 3 cm. They normally weigh between 15 and 30 grams, although males are slightly larger than females, especially in the skull. The short-tailed shrew is a stout shrew, with a shorter and heavier snout than some of its relatives. Its eyes are small, and its ears are almost hidden in the fur.

Northern Short-tailed Shrews belongs to the genus Blarina, the red-toothed shrews. They generally live in densities of 2-12 shrews per acre, and the typical home range of a shrew is slightly over 6 acres. They are solitary animals, and the males aggressively defend their territory and mark it with scent from scent glands on their belly and sides. Territories tend to overlap slightly during the breeding season.

Shrews are thought to have very poor eyesight, and are possibly only able to distinguish light from dark. However, they have a very keen sense of touch. They are also known to use echolocation largely to determine their surroundings, and can produce ultrasonic clicks and listen to the returning echoes to detect the objects nearby.

B. brevicauda inhabits disturbed and undisturbed areas: forests, marshy areas, fields, gardens, fencerows; anywhere with sufficient vegetation and groundcover to for them to tunnel in. These shrews generally tunnel belowground, through leaf litter, or between the snow and the ground. Elaborate tunnel systems may be constructed, with deep nests for the wintertime, as well as latrines, storehouses for food, and mating nests for raising their young.

These shrews do not hibernate; rather, they curl up in a deeply lined nest in the wintertime and forage more during the day when it is warmer, rather than at night as they mostly do in the summer. They also cache food in their burrows in case of a prey shortage, decrease their activity levels during cold periods, and use nonshivering thermogenesis, a biochemical method of creating body heat. In spite of all this, the mortality rate over the winter sometimes exceeds 90%.

In spring or early fall, B brevicauda builds complex mating nests that can reach 25 cm across in their tunnels or under logs or rocks. After copulation, a female will gestate for 21-22 days, after which she will give birth to around 5-7 pups, although litters of 10 have been documented. The pups, which are blind and hairless at birth, will remain in the nest for 18-20 days, and are weaned several days later. Being weaned is the end of parental care for the pups. The females become sexually mature at only 6 weeks old, while the males take twice that long, or 3 months. These shrews can live up to 3 years, but the mortality rate is very high; most probably die in their first year.

The Short-tailed Shrews have venom in their bite which paralyzes prey larger than the shrew itself. While not too dangerous to humans, it can cause extreme swelling and considerable pain. The venom enables them, in addition to a diet of invertebrates and plant material, to catch and consume salamanders, birds, snakes, mice, frogs, and other shrews. They are opportunistic foragers, and can consume up to 3 times their body weight in a single day. This is because of their extremely high metabolism. So high, in fact, that they must eat every three hours to keep from starving to death.

They are predated by a variety of creatures, including snakes, raptors, cats, raccoons, etc. However, the scent glands on its belly make it distasteful to many predators; also, it is quite fierce and can repel an intruder effectively.

This specimen was accidentally captured by Courtney in a live mouse trap.

Article by Hazel Galloway