The spring molt begins in May or June, whereas the autumn molt begins in September, but the tail only molts once each year in the summer. Douglas squirrels have four sets of whiskers located above and below the eyes, on the underside of the head in front of the throat, and on the nose. Whiskers, also known as vibrissae are touch receptors that provide the animal with information about its immediate surroundings. Douglas squirrels have very good eyesight even in dim light, and a wide field of vision. They also have a well developed sense of smell and hearing.
Squirrels have upper and lower incisor teeth followed by a gap called a diastema.
The diastema is where the canine teeth would normally be found in carnivorous animals such as cats or dogs, or omnivorous animals such as monkeys. Behind the diastema are the cheek or grinding teeth which consist of premolars and molars. As with other rodent species, the incisors continuously grow to compensate for the enormous amount of wear that comes from a herbivorous diet. Young squirrels have milk teeth which are replaced by permanent teeth when they are between six and twelve months old. Douglas squirrels are highly adapted for climbing trees and fatal falls are rare.