The cinereus shrew, often called the masked shrew, is a mammal in Colorado’s records. That ranking is almost entirely a product of scientific collecting: open occurrence databases hold 1,155 Colorado records, and virtually every one is a museum specimen or a live-trap capture, not something a person spotted and photographed.
A tiny shrew of moist mountain ground
Barely heavier than a coin, the masked shrew is a high-country animal in Colorado. Records concentrate in the western mountains, thickest in Pitkin, Boulder, Larimer, and Eagle counties across the montane and subalpine zones. It hunts through the damp microhabitat of the high forest, streambanks, wet meadows, willow carr, and the moist litter under spruce and fir, where it works the runways of voles and the spaces beneath logs and moss in near-constant search of insects, worms, and other invertebrates.
Counted from the trap line
The gap between the record total and the near-total absence of photographs is the honest story. A shrew this small, secretive, and fast is effectively unphotographable in the wild, so its whole Colorado record is built from small-mammal survey trapping and preserved specimens accumulated over decades of field work. A high count here means biologists have trapped these mountains hard, not that the animal is easy to encounter. Its S5 rank marks it as secure and genuinely widespread across the high country.
A record shaped by the field season
The apparent summer surge is a fieldwork signal, not a biological one. The masked shrew stays active all year, hunting under the snow through winter because its racing metabolism never lets it rest for long. The records bunch into July through September because that is when crews can reach high-elevation sites and run trap lines, so the calendar shown is really the survey calendar.
Full species profile
