Like most male mammals, a male squirrel possesses testicles, or testes, which are necessary for the species’ continuation. The confusion about their presence stems from a unique biological adaptation that controls their external visibility. Understanding the male squirrel’s anatomy and how it responds to seasonal changes provides a clear answer to this common observation.
Male Squirrel Reproductive Anatomy
Male squirrels do have testes, which are the primary reproductive organs responsible for producing sperm and testosterone. These organs are held within a small pouch of skin called the scrotum, located externally near the base of the tail. This external positioning is standard for most mammals, as sperm development requires a temperature slightly lower than the core body temperature. The appearance of the scrotum in squirrels differs from that in many domestic animals, as it is often a small, dark, or slightly pigmented bulge. During the breeding period, the testes enlarge considerably, making the scrotal sac much more pronounced and easily observable by a casual viewer.
Seasonal Visibility and Retraction
The visibility of a male squirrel’s testes is not constant; it is directly linked to the annual breeding cycle and environmental conditions. Squirrels exhibit a phenomenon known as seasonal cryptorchidism, where the testes regress in size and are temporarily drawn up into the inguinal canal or abdominal cavity during non-breeding periods. This retraction protects the organs from injury and harsh cold.
Testes recrudescence, or growth and descent, typically begins in late autumn or early winter, reaching full size by mid-December for the first breeding season. The male squirrel often experiences two main periods of sperm production annually: one in the winter, from approximately December to February, and a second in the summer, around May to July. During these active phases, the testes can swell to nearly seven times their regressed size, making them highly visible.
As the breeding season concludes, usually from late summer through the autumn, a dramatic testicular regression occurs. The testes can shrink by as much as 90% of their active mass, and the scrotum becomes noticeably empty and inconspicuous. This quiescence period, which may last from August to November, is why observers often believe the male squirrels lack external reproductive organs. The timing of these cycles is also heavily influenced by food availability and local weather conditions, making the visibility somewhat variable year to year.
Identifying Squirrel Sex Without Testes
When the testes are retracted and the male is in a non-breeding state, determining the sex of a squirrel requires looking for other subtle external differences. The most reliable visual cue is the anogenital distance, which is the space between the anus and the other opening. This distance is significantly greater in males than in females because the male’s urogenital opening is further away from the anus.
Another helpful, though not always present, indicator is the presence of nipples, which are a definitive marker for females. While nipples are difficult to see on non-lactating females, they become distinct and enlarged on a female who is actively nursing a litter. Observing the squirrel’s behavior can sometimes offer clues, as a male may be seen pursuing a female during a chase, or a female, often called a sow, may be seen carrying nesting materials.