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Gray squirrels (Sciurus carolinensis) are small rodents native and common to the United States’ eastern and midwestern regions, and found in other regions and countries through non-native introduction. Male squirrels are called “boars” and female squirrels are referred to as “sows.” From a distance, it can be difficult to tell them apart, but close observation of physical characteristics and behaviors -- especially those associated with reproduction -- can reveal a squirrel’s sex.
Often, a mammal’s sex can be determined by its size, fur coloration or other physical attribute. Gray squirrels, however, are not so easily distinguished by these characteristics. Male and female gray squirrels both weigh 1 to 1 1/2 pounds at maturity and measure about 18 inches in length. About half of their length comes from their large, bushy tails that also do not vary in appearance between sexes. These similarities make sexing gray squirrels from a distance -- such as in the backyard -- difficult or impossible.
When much closer to a gray squirrel -- such as in a veterinary examination -- the sex of the animal can be determined by viewing its reproductive organs. Like most mammals, male gray squirrels have a outwardly visible penis and scrotum, while females have a visible vaginal area. During mating season, a gray squirrel’s testes are swollen and the scrotum is fully descended. This is one of the only times a typical backyard observer may be able to determine a squirrel’s sex, though close range is still needed.
A gray squirrel’s sex can also be determined by observing mating chases that occur in mid-summer and late winter. When females are in estrus, meaning they are ready to mate, they attract males with their scent. One or more males will vigorously chase the female for a mating opportunity. It's generally clear in the mating chase which squirrel is the receptive female and which are the attracted males, confirmed if the mating ritual is observed. The hierarchy of male squirrels can also be observed, as the dominant male is typically the one that will mate with the female.
Parenting behaviors also help indicate male and female squirrels. Females bear and raise their young in dens and keep to a very small territory while with their young. At about 6 weeks old, the young start to leave the den, but remain close to their mothers for at least several more weeks. When observing an adult squirrel with juveniles, the adult is typically female and their mother. Male and female squirrels do not form pair bonds, so the male is not typically seen with its young or in the female’s den.
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