I awoke to a thump on the roof and a quick series of pattering footsteps. Within seconds, a second thump and pattering. Then a third thump. That provided all the clues I needed. At least one of my eastern gray squirrels approaches estrus.
For the last few days, I have seen a male squirrel following close behind a female, waiting for her to be physically ready to mate. Most of the year, one cannot tell a male squirrel from a female. The old timers claimed that the female castrated the male. An informal study by Georgia Outdoor News showed that 21% of the relatively small sample believed squirrels did get castrated. We now know this is not true, but most of the year, the male’s testes are contracted inside the body and the scrotum shrinks. Think about it. An animal that spends its life running around in trees jumping from branch to branch would benefit from a retracted scrotum. But, twice a year, this changes. Around December to February and again in May and June the females become fertile.
The male’s body also prepares for mating. At this time, the males travel great distances to search for potential mates. When they discover one, they will follower her for several days, always close at hand. Other males will also be attracted to this female and chases commence.
During the brief interval (as short as 8 hours) when a female can conceive, the activity ramps up with more chasing and aggression. I am sure this is what I heard on my roof this morning. It is wonderful how a few simple sounds can tell a whole story when one learns to listen.

Additional Reading:

http://forum.gon.com/showthread.php?t=479451
http://animaldiversity.org/accounts/Sciurus_carolinensis/
http://animals.mom.me/tell-male-gray-squirrel-female-squirrel-5994.html
http://sciencing.com/tell-squirrel-male-female-7770857.html