Giant Panda Estrus FAQs

Breeding season for giant pandas is usually in the spring from March to May. Although the breeding season lasts for several months, a female giant panda is only capable of conceiving a cub for 24 to 72 hours once a year. In the wild, male giant pandas may breed with multiple females throughout the breeding season.

When the breeding season is approaching, giant pandas are generally more restless than at other times of the year. They can frequently be seen patrolling their territories, investigating scent markings left by other pandas, leaving scent marks, climbing trees, playing in water and making bleating and chirping vocalizations.

Males will mark their territories doing a behavior called “urine hopping” (which looks like they are hopping on one foot as they urinate). They will also attempt to make their urine marks as high as possible on trees and other structures. When they do this, they look like they are doing a handstand. They will bleat to females to show their interest.

Female pandas will bleat to the males and eventually make a “chirping” vocalization to show interest. If a female encounters a male, she will raise her tail and walk backwards toward him to indicate she is receptive to breeding.

Tian Tian usually becomes very playful and restless during breeding season. He spends much of his time scent-marking, playing in water, patrolling his yard and vocalizing to Mei Xiang.

Mei Xiang’s behavior can sometimes be more subtle than Tian Tian’s before breeding season. She will spend more time scent-marking and investigating Tian Tian’s scent marks. She also paces and spends time in the pools and water features in her enclosures. Generally, she does not spend very much time interacting with Tian Tian unless she is in estrus (the very short window when she is able to conceive a cub). Her vocalizations toward him become more friendly when she nears estrus.

Female pandas will make a “chirping” vocalization to attract any nearby males and indicate they are ready to breed. If they encounter a male, the female will raise her tail and walk backward toward him to indicate she is receptive to breeding. Mei Xiang will do this toward Tian Tian at the window between their yards.

Yes, she has in the past, but she was nursing a cub each time. Giant panda breeding season is typically from March to May.

Mei Xiang is near the end of her reproductive life cycle. Even if Mei Xiang is an aging female, her hormones, vaginal cytology, and behaviors progressed in the same way as they have in past years, from the onset of breeding season until the day of the artificial insemination. Hormone profiles observed during her pregnancy were also normal. At her current age of 22, Mei Xiang would be the oldest giant panda to give birth in the United States. The oldest giant panda to give birth to a cub on record was a 23-year-old female panda in China.

Behavioral cues are one way to determine when breeding season has arrived. Because the window when Mei Xiang is able to conceive a cub is very short (24 to 72 hours), endocrinologists at the Smithsonian Conservation Biology Institute monitor the levels of estrogen and progesterone in her urine. When they see her levels of estrogen rise, that means Mei Xiang is in estrus. After her estrogen levels peak, it indicates that she is ovulating. Reproductive physiologists also monitor physical changes that indicate Mei Xiang is getting ready to breed.

Urine samples are regularly collected. The samples are sent to the Smithsonian Conservation Biology Institute for analysis weekly, but increase in frequency of analysis as Mei Xiang gets closer to estrus. When she enters peak estrus, the team stays overnight to collect all of her urine in order to predict her ovulation.

Urine is collected with a syringe from the floor of Mei Xiang’s enclosure. She tends to urinate in the same spots each day.

Giant pandas are solitary, and adults do not spend much time interacting outside of the breeding season. If we were to allow Mei Xiang and Tian Tian to spend time together before Mei Xiang was ready to breed, they would likely be aggressive toward each other. In the wild, a female would avoid males until she is ready to breed.

Mei Xiang is capable of conceiving a cub once she has ovulated (after her estrogen levels have risen, peaked and started to fall). When her estrogen is back to normal levels, or what our scientists call “baseline levels,” her estrus and breeding season is finished. Scientists usually start to see Mei Xiang's estrogen levels rise for several days before they peak. After they peak, her hormone levels usually return to normal within 72 hours.

If Mei Xiang shows interest in breeding with Tian Tian, we will give them the opportunity to spend time together and attempt to breed naturally. Our panda team, which includes Smithsonian Conservation Biology Institute scientists, Zoo veterinarians and keepers, will perform one or more artificial inseminations in addition to natural breeding.

Female giant pandas experience the same behavioral changes and hormonal changes if they are pregnant or pseudopregnant (not pregnant). Even if Mei Xiang is not pregnant, she will still build a nest, spend time body-licking, cradle objects and sleep often. Her levels of progesterone will rise and fall just as they would during a real pregnancy. The only way to definitively determine if a female is pregnant is to detect a developing fetus on an ultrasound.

A pseudopregnancy mimics a real pregnancy, but instead of giving birth at the end of it, a giant panda's hormones and behaviors return to normal.

Mei Xiang and Tian Tian have been given the opportunity to breed naturally nearly every breeding season, but the panda team has never observed successful breeding from them.

We separate Mei Xiang and Tian Tian immediately after breeding attempts to prevent any aggression. Males often act aggressively toward females once females' hormones start to decrease.

We don’t know definitively when Mei Xiang will be past breeding age. Based on the data from scientists in China and other zoos with pandas, females can breed until their early twenties. The panda team will not attempt to breed Mei Xiang again after this year.

Panda gestation length ranges from 90 to 180 days, with an average pregnancy lasting 135 days. This wide variation in gestation occurs because the fertilized egg usually floats freely in the mother's uterus before it implants and begins developing. Once the embryo is attached to the uterine wall, its development continues until a panda is born; newborn pandas are blind, very small and without almost any fur. A newborn panda weighs about 3-5 ounces. In American black bears, the actual period of time that the embryo develops following implantation is about eight weeks. For pandas, actual development time is probably similar. Much of a panda's physical development occurs after birth.

For more information about panda cubs, check out the Giant Panda Cub FAQs.