Daily Activity of Short-tailed Shrews (Blarina brevicauda) in Simulated Natural Conditions

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Long-term measurements of the activity of eight short-tailed shrews (Blarina) were made in simulated natural conditions. A significant correlation (p 30 % ) were observed in summer. Temperature was significantly correlated to activity near midnight, but time active out of the nest during midday remained near 10% regardless of temperature. These shrews appeared to adjust their activity levels and patterns to avoid temperature extremes. INTRODUCTION Daily activity patterns of mammals are probably controlled by their rate of metabolism and, hence, their need for rest and food at regular intervals (Crowcroft, 1957). The activity patterns of each mammal should, therefore, be related to how it meets its energy needs and how it expends energy. Activity patterns and factors affecting these patterns are particularly interesting in shrews due to the relatively high metabolic rate and small size of these insectivores (Pearson, 1947; Deavers and Hudson, 1981). The activity patterns of captive Blarina brevicauda have been described by several authors (Buckner, 1964; Lutz, 1964; Martinsen, 1969; Mann and Stinson, 1957; Pearson, 1947; Randolph, 1973). Studies of Blarina activity in the wild are less common and generally based on trapping results (Fitch, 1954; Lutz, 1964; Pearson, 1947; Platt, 1972; Randolph, 1973); only one study directly measured activity of free-ranging Blarina (Ostenberg, 1962). Most authors report primarily nocturnal activity for Blarina as well as other shrews (e.g., Crowcroft, 1954). (See Martin, 1980a, for a more detailed review of this literature.) Comparisons of Microtus pennsylvanicus activity in laboratory and in enclosed field conditions have shown that laboratory conditions significantly changed activity patterns (Graham, 1968). Thus, natural conditions were simulated here to produce the most natural activity patterns while allowing, through long-term recording, detailed analysis of specific factors affecting daily and seasonal fluctuations in Blarina activity. METHODS AND MATERIALS Simulated natural conditions. Short-tailed shrews used in this study were live-trapped in active runways under forest leaf litter in central or western Massachusetts (four male, one female) or born in captivity (two male, one female; see Martin, 1980a). Shrews were placed in the simulated natural conditions within 24 hr of capture. Activity was measured in adult individuals only. Simulated natural conditions for these short-tailed shrews were established in five lx3x2.5 m rooftop cages in Amherst, Massachusetts. [These conditions were used to study various aspects of Blarina behavior (Martin, 1980a, 1981) and thus contained certain features which would be unnecessary for a study of activity alone.] To simulate a forest canopy, the cages were open to the weather on the sides, but covered with black polyethylene on the front and top. The floors of the cages were covered with approximately 2-4 cm of forest soil which in turn was covered by a layer of leaf litter. Light intensity was measured with a photographic light meter and the daily minimum and Address reprint requests to latter address.