When threatened, the bird stretches its body and tightens its feathers in order to look like a branch stub to avoid detection, but will take flight when it knows it has been detected. They have noticeable light spotting along the edge of the scapulars. There is much individual variation within the two colour morphs. In the grey-phase, birds in the dry southwest are a paler grey, while birds in the humid northwest are darker and browner. The red-phase is very rare and found only in the Pacific Northwest.
Facial disks are dusky white with fine grey-brown mottling.
The legs have fine buff mottling. The face is buff light cinnamon. There is rufous spotting on the breast with black anchor marks. The juvenile of both colour phases is similar to the adults, but the indistinct stripes and bars are more patterned, with many feathers tipped with white. The Western Screech Owl is likely to be confused with the Eastern Screech Owl and Whiskered Screech Owl.