By Chuan-X Panda
Updated: Sep. 14, 2025 10:30 AM
Giant pandas are notably large animals. In the wild, adult pandas typically weigh between 80 and 100 kilograms, while those in captivity can reach weights of 80 to 130 kilograms, with the largest individuals growing up to 180 kilograms. Their appearance—round and monochrome—often resembles large black and white balls. In stark contrast, newborn panda cubs are extremely small, with an average birth weight of only about 100 grams.
The smallest panda cub on record weighed just 42.8 grams. On July 11, 2019, a giant panda named “Cheng Da” gave birth to twin sisters at the Chengdu Giant Panda Breeding Research Base. The older sister weighed 171.9 grams at birth, while the younger one was a mere 42.8 grams. This weight is even lower than that of the previously smallest cub, “Wu Yi”, born in 2006, who weighed 51 grams at birth. Thanks to dedicated care from breeders, Wu Yi has now grown to over 130 kilograms. The weight ratio between a newborn panda and its mother is an astonishing 1:900—one of the most extreme among mammals. For comparison, the ratio is about 1:22 in humans, 1:120 in Bengal tigers, 1:10 in giraffes, and 1:45 in African elephants.
So why are newborn pandas so tiny?
1. Giant pandas are not marsupials.
First, it is evident that marsupials give birth to relatively underdeveloped offspring. This is largely tied to their reproductive strategy. Marsupials do not possess a true placenta; instead, their young are born in an extremely premature state and continue their development externally—typically within the mother's pouch. There, the newborns suckle and grow in a protected environment. Thus, what is often called “birth” in marsupials is more accurately an early transition to external development, facilitated by the pouch.
Marsupials are classic examples of altricial species, meaning their young are underdeveloped at birth. In contrast, many other animals in nature are precocial—they undergo extensive development in the womb and can become independent shortly after birth. For instance, some ungulate mammals, which play a crucial role in the food chain, face constant predation pressure. To enhance their chances of survival, their newborns must quickly adapt to the environment. A good example is the giraffe: its calf weighs about one-tenth of the mother's weight at birth and can stand up and run fairly soon after delivery.
Giant pandas, however, are not marsupials. Despite being placental mammals, their newborns are exceptionally small, which significantly reduces their survival rate in the wild. This is one key reason why panda populations have remained low for so long.
2. Giant pandas embryos undergo delayed implantation.
Scientists have discovered that giant panda embryos undergo delayed implantation. After fertilization, the egg remains free-floating in the uterus for about one to three months before implanting. Only when conditions are favorable does implantation occur. The total gestation period ranges from 84 to 160 days, meaning the actual embryonic development time is nearly halved due to this delayed implantation. As a result, newborn pandas weigh only around 100 grams—a direct consequence of this unique reproductive strategy.
3. Lack of foods and nutrients during pregnancy.
In the wild, the gestation period of giant pandas often coincides with winter. During this season of scarce food resources, ursids such as bears typically hibernate, surviving without food or water by relying on stored fat reserves. To minimize energy expenditure in pregnant females, scientists suggest that giant pandas have evolved to give birth to highly underdeveloped offspring. This strategy ensures that the cubs require minimal energy intake initially, while continuing their development externally through milk feeding. Existing studies further indicate that pregnant pandas experience a significant reduction in appetite and markedly decreased nutrient absorption.