Their sense of smell is thought to be poor, and their eyes are degenerated and vision is thought to be limited to the detection of light, but the shrew compensates by using echolocation and a fine sense of touch. Energetics Its ability to consume almost anything it can catch allows the northern short-tailed shrew to survive the cold winters of temperate regions. The thermoneutral zone of this species is from 25 to 33 °C, meaning no extra energy must be expended by the animal to maintain its body temperature (which averages 38.0–38.5 °C) when the ambient temperature is within this range. Food consumption is 43% higher in winter than in summer, as the shrew must increase its metabolic rate to maintain its body temperature under the cold conditions. Temperatures at or above 35 °C are lethal for this shrew. A study of captive shrews found, though they were primarily nocturnal, the degree of nocturnality changed with the season; that is, during the colder winter, the shrews exhibited more out-of-burrow activity earlier in the evening, but were active later in the night during the summer. This seasonal pattern was due to solar radiation and changing daily temperatures, and it allows the shrews to minimize the energy needed for thermoregulation. Other winter adaptations include the creation of a lined nest which aids the shrew in conserving heat, the caching of food in case of prey shortages, foraging below the leaf litter or snow where the temperature is milder, and decreasing activity levels during cold periods. Along with these behavioral adaptations, the northern short-tailed shrew increases its ability to generate body heat during the winter by nonshivering thermogenesis in brown adipose tissue. Behavior Other shrews spend more time above ground than does the northern short-tailed shrew, which prefers to tunnel along below ground, through the leaf litter, or at the snow/ground interface. Bouts of frenzied activity, lasting around five minutes, are followed by longer periods of resting, with the total active time amounting to only 16% of a 24-hour day. This animal is capable of digging at a rate of 2.5 cm/min, in between resting. The shrew constructs a nest up to in diameter underground or underneath a log, and lines it with leaves or the fur of the meadow vole (Microtus pennsylvanicus). This nest is kept clean, with wastes deposited outside the nest in a latrine area. Other parts of the burrow