Giant pandas usually go into heat in spring and give birth from summer to early autumn. In captivity, 92% of births occur between June and September, making winter births rare. There have been 7 recorded winter births (November-December) in captivity, and 4 of those (1 in November, 3 in December) happened right here at our park. (Figure 1)

Figure 1. Number of births per month

1. Out-of-season estrus

Table 1 shows the breeding patterns observed at our park. We've identified two patterns for winter births: one where mating happened a bit later than usual, extending the gestation period and leading to winter births (like in 2020), and another where estrus and mating occurred out of season, from summer to early autumn, also resulting in winter births (seen in 2001, 2006, and 2014).

Table 1. Breeding Patterns

◆: Mating ●: BirthA: Seasonal (spring) estrus and mating, births from August to SeptemberB: Mating a bit later than usual, longer gestation period, winter birthsC: Out-of-season (summer to early autumn) estrus and mating, winter births

We compared the timing of estrus signs for each estrus stage between seasonal estrus (7 cases) and out-of-season estrus (3 cases) (Table 2). When we looked at when males showed signs in the proestrus stage, for seasonal estrus, it was much earlier than females, about 2-3 months prior. However, for out-of-season estrus, it was observed a few days later than females. This suggests that males' behavior is likely triggered by the females' estrus signs. (For details on estrus stage classification, please refer to this page)

Table 2. Comparison of Estrus Stages in Seasonal and Out-of-Season Estrus

2. Important Points for Winter Births

Managing room temperature and humidity is super important when animals give birth in winter. Keeping the room temperature just right is a must to help newborns stay warm, but managing humidity is also key so the mom can focus on raising her babies. When humidity dropped below 50%, moms' skin would get dry and itchy, and they'd often scratch themselves with their claws, which made it hard for them to concentrate on their little ones. So, for winter birthing rooms, we figured an ideal environment would be around 20℃ for temperature and about 60% for humidity. (See Table 3)

Table 3. Temperature and Humidity in the Birthing Room