Red panda mating coincides with the winter solstice and occurs in early winter, usually within January and March.
In captivity, red panda mating is strictly seasonal with onset in the early winter, usually between early January and mid-March. The onset of sexual activity coincides closely with increasing photoperiod following the winter solstice. The mating season for individuals in captivity in the northern hemisphere seems not to differ substantially from that in the wild, although there may be a tendency for prolongation of the mating season in captive colonies. Captive individuals in the southern hemisphere mate in the austral winter, generally in July and August.
A hierarchy of environmental cues trigger reproduction in captivity; photoperiod is a general cue and lunar periodicity is a more specific cue, with copulations tending to cluster during the “new moon” phase of the lunar cycle.
Testis size in captive male red pandas undergoes seasonal change, being small and semi-abdominal from April to November and large and scrotal during the premating and mating period in the northern hemisphere.
In the wild, births occur in spring and summer, but mainly in June. In captivity in the northern hemisphere, 3.5% of 199 litters were born in May, 79% in June, 16% in July, and 1.5% in August. Of 11 litters born in the southern hemisphere, 8 were in December, 2 in January, and 1 in March.
In captivity, no synchrony of mating or birth dates is evident among females housed in the same or nearby enclosures. The time of mating and birth is also not affected by latitude, (within a hemisphere,) or by altitude. Females tend to give birth within 10 days of the date of parturition the previous year.