The smoky shrew is a relatively large Sorex, heavier and more powerfully built but with a shorter tail, than Sorex dispar which occupies part of its range.It is much larger than the common masked shrew, Sorex cinereus cinereus, which is occasionally found in the same runways.The winter pelage differs decidely from that of the summer pelage.In winter the upperparts are deep mouse gray or slaty; the underparts are very much lighter, almost silvery.Some specimens have a butty surfusion in the post-abdominal region.In summer pelage the upperparts are pale grizzled brown, the hair tips of the underpart being paler and gray at the base.The tail at all seasons is bicolored, straw yellow below and brown above.I have seen no aibinistic specimens but old specimens occasionally have the hair tipped with white, or there may be a small patch of white fur on the thigh.Summer specimens may be confused with Sorex cinereus (Townsend, 1935), but their gi'eater size and darker color serve to distinguish them from their lesser kin.Measurements.Three conventional measurements are made of mammals when they are caught and before they are made into scientific specimens, viz., total length (nose to end of last tail vertebrae) ; tail (base of tail to end of last tail vertebrae) ; hind foot (heel to end of longest claw).These measurements, unfortunately, vary with the collector and his methods, the condition of the specimen whether fresh, bloated, in rigor mortis, etc., and are largely a matter of personal equation.All the measurements listed below were made by myself, from freshly caught specimens taken in New York State.Adult males.Twenty-six specimens average: total length, 116.5 mm.; tail, 41 mm.; hind foot, 13 mm.Adult females.Twenty-two specimens average: total length, 116.3 mm.; tail, 43 mm.; hind foot, 12.6 mm.Immature males.Seventeen specimens measure: total length, 113.5 mm.; tail, 41.4 mm.; hind foot, 12.7 mm.Immature females.Fourteen individuals measure: total length, 113.1 mm.; tail, 41.2 mm.; hind foot, 12 mm.Thus the measurements of 48 adults of both sexes average : total length, 116.4 mm.; tail, 41.9 mm.; hind foot, 12.8 mm.Thirty-one immature specimens average: total length, 112.8 mm.; tail, 41.3 mm.; hind foot 12.6 mm.It is thus evident that the conventional external measurements provide little data on relative age, at least with this species.It is my belief that this is true of many small mammals.This belief is based on measurements of many hundreds of small mammals of various species in northeastern United States.Weights, external appearance (pelage, hairy tail tufts or bare tail tips, scarring of tail and feet) and above all, weight give a good index to the age of this shrew, and combined, are sufficient in themselves to give a ready clue to the approximate age of the animal.Tooth color and wear are infallible, and should always be resorted to in order to determine the age of the individual.Weight.The smoky shrew has a variable weight, depending upon the amount of food it has recently ingested and also on its condition.Sufficient numbers, however, taken throughout the year, show a remarkable difference between the immature and mature animals, and the two may readily be separated on this factor alone.Recently weaned shrews, about one month old, weigh 4 grams.They gain weight slowly and throughout the first 7 to 10 months of their lives weigh from 4 to 6.8 grams.Immature individuals of both sexes collected from June to November weigh from 5.5 grams to 6.8 grams, the average of 97 specimens of both sexes being 6.19 grams.There is no sexual variation in the weight of immature shrews.
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W. J. Hamilton (1940) studied this question.