Sorex trowbridgii [Baird]
Trowbridge shrew
Description.—The Trowbridge shrew closely resembles the cinereous shrew in body form but possesses a longer tail. The head and body of adults measure about 2-1/4 inches and the tail about 2 inches. The Trowbridge shrew may be separated from all other small shrews that occur in Washington by its dark bluish upper parts and bluish or slaty underparts. The tail is distinctly bicolor.
Trowbridge shrews occur from southern British Columbia south to central California. Their distribution, to the south, is more extensive than that of many members of the Pacific Coastal Fauna. They are forest animals, ranging widely over the dry ground beneath the fir forest, where they are usually the only shrews present. They are abundant in ravines and in some swampy woods when other shrews are absent, but they avoid open meadows or marshes. Vertically, they occur from the humid division of the Transition Life-zone to the Hudsonian Life-zone.
These little shrews do not live well in captivity and I have learned relatively little concerning their habits from live specimens. They seem to be slower-moving and less aggressive than the wandering shrew. Population studies showed that the Trowbridge shrew is unable to compete with the wandering shrew in ravine habitats ([Dalquest], 1941A: 173). The principal food of the Trowbridge shrew includes soft-bodied insects and insect pupae.
Fig. 28. Distribution of the [Merriam] and Trowbridge shrews in Washington. A. Sorex merriami merriami. B. Sorex trowbridgii trowbridgii. C. Sorex trowbridgii destructioni.
[Moore] (1942) has shown that shrews eat the seeds of the Douglas fir and may be a serious check on the reproduction of this important tree. The Trowbridge shrew is the most abundant shrew in the fir forests and probably constitutes the principal shrew that might be classed as a pest.
A specimen containing 4 embryos was taken near Shelton, Mason County, on April 23, 1937. Males with enlarged, greenish testes were taken in April of 1938, 1939 and 1940. Specimens obtained in other months showed no indications of breeding.