Giant pandas typically become sexually mature between the ages of five and seven, with males maturing later than females. Captive giant pandas may become sexually mature a year earlier than wild giant pandas, between ages four and six.
The female giant panda goes into estrus (heat) only once a year, usually in the spring, for a period of approximately 48 hours. They conceive only during their two- to three -day estrous period, and show no interest in mating at any other time. Males are sexually active for a longer period in the spring, which in the wild would allow them to attempt to inseminate more than one female. (In captivity, it means they annoy their partner for most of the spring.)
One or two weeks prior to estrus, the female’s nipples and genitals begin to swell and redden, and she becomes extremely restless, moving constantly to change positions, rolling on the ground, and bathing more frequently. She also vocalizes more, by bleating, chirping, and grunting. Although females scent mark throughout the year, her scent marking increases dramatically. She will walk backward while tossing her head and bleating. Given her lack of interest in mating for the rest of the year, this behavior is generally quite obvious to even untrained observers.
When a male is present, the female giant pandas allows courtship by becoming less aggressive and determined to mate. She allows the male to approach and follow her, and may even solicit his attention by backing up to him. She elevates her posterior, raises her tail, and lowers her forequarters so there is a depression in her back. She may tuck her head under her chest or brace it against a wall or tree while her hindquarters are elevated. If he doesn’t respond, she may roll onto her back, begin squirming and writhing, and reach out to him with her forepaws. The male being courted may sniff and manipulate her tail region; scientists believe the scent may prepare him for mating.
During copulation, the male stands almost upright behind the female, raising his head, bleating, and making mouthing gestures reminiscent of a carnivore neck bite. He mounts and dismounts constantly before actual intromission. In captivity, a number of male pandas (except for Gao Gao in San Diego, who was born in the wild) have had difficulty with copulation, and have to be separated from their female partners during the critical estrus period to permit artificial insemination.
After a few days of intense mating, the couple separates to resume their more solitary lives. (Whew, that’s finally over with, she says.)