Giant female pandas are in heat -- or able to conceive -- only once per year for approximately two days. After natural mating or artificial insemination, they often undergo what is called a pseudo pregnancy in which their bodies -- including hormonal levels -- experience all the signs of pregnancy without actually being pregnant. Identifying the signs of pregnancy in this endangered species plays a guiding role in breeding programs worldwide.
When giant pandas are within 40 to 50 days of giving birth, they tend to lose their appetites, according to Live Science. This outward sign is relatively easy to detect as on average an adult giant panda eats 19 kilograms -- just short of 42 pounds -- of bamboo per day, according to World Wildlife Fund Panda Central. This means adult giant pandas are dining up to 14 hours a day, according to Pandas International. When this behavior stops in a female, pregnancy is one of the suspected causes.
Rather than eating the bamboo given to them in captive settings such as zoos, a pregnant giant panda getting closer to her due date occupies herself with shredding the bamboo into little pieces to make a nest, according to Live Science. This "nesting" behavior is one that researchers at the Smithsonian National Zoological Park watch for after performing artificial insemination to try and impregnate the facility's pandas on loan from China. In the wild, pregnant pandas build a nest, lining it with material such as wood chips, birch or fir saplings and branches from rhododendron or bamboo to keep out damp and cold, as explained by Think Quest. In captivity, human caretakers provide these materials to facilitate the behavior.
When a fetus shows up on ultrasound, researchers working with giant pandas become confident a pregnancy is in place. Such was the case at Zoo Atlanta in late October 2010 when months-long suspicion and hope that the zoo's 13-year-old giant panda Lun Lun conceived after being inseminated earlier in the year, as reported by NBC News. Yet ultrasound isn't always an accurate detector of panda pregnancy. A panda fetus -- even when close to birth -- is quite diminutive compared to its mother. It's about the size of an eraser and difficult to detect because it's hidden under its mother's layers of fat, her bladder and a stomach full of digesting bamboo. A panda fetus can also go undetected because they don't begin to develop fully until the last couple weeks of pregnancy, according to NBC Washington.
A Cub is Born
As obvious as it sounds that the birth of a cub is a sign of panda pregnancy, it's one signal relied upon for confirmation, albeit slightly after the fact. Researchers at the Smithsonian National Zoological Park regularly tell media reporting on the zoo's renowned breeding program that even with the use of ultrasound, they don't count on a pregnancy until a cub is born.
- Smithsonian National Zoological Park: Giant Pandas: 2009 Pregnancy Watch
- Live Science: Perplexing Panda Pseudo-Pregnancy Pondered
- NBC News: Zoo Atlanta: Giant Panda Lun Lun Is Pregnant
- Pandas International: Giant Panda
- PBS: Why Pandas Have Trouble Getting Pregnant
- NBC Washington: National Zoo Can't Say Yet If Panda Is Pregnant
- Tom Brakefield/Stockbyte/Getty Images