Bone density in big cats: zoos vs. the wild

A recent study by an international team of scientists has tested the expectation that big cats in the wild exhibit greater bone density than their captive counterparts. The results of which affect future comparative studies and rewilding programs!

Bones respond to mechanical loading; the stress placed on bone can lead to greater or lesser bone density. A recent study in Royal Society Open Science, with scientists from Marshall University, the Australian Museum, the National Museum of Natural History and John Hopkins University investigated the differences in bone density between animals kept in zoos and those derived from the wild. The results of which have far-reaching and considerable impacts, for future studies and rewilding programs.

Studies from the past 100 years comparing animals in captivity and the wild have suggested a range of morphological differences – some of the more extreme skeletal and dental changes in animals in captivity have been attributed to unnatural diet and limited mobility. Animals in captivity generally grow to be larger and mature faster than those in the wild, and most comparative studies have focused on cranial dimensions and size, but few studies have focused on post-cranial bones of wild and captive animals.

This team compared the trabecular bone (also known as spongey bone, indicated below) between wild and captive mountain lions, cheetahs, leopards and jaguars. They studied the BVF (bone volume fraction), a measure of how much bone is in a joint or how dense a bone is, of the fore and hind limbs. Specimens were analysed from the National Museum of Natural History (NMNH) at the Smithsonian Institution in Washington, DC, and from the American Museum of Natural History in New York.

The research found that animals in zoos had significantly lower bone density than their wild counterparts, suggesting that restricting physical activity results in a decline in bone density and consequently bone strength.

In regard to the impacts of these results, this research urges caution in using skeletons of animals from zoos in comparative studies. These findings also have implications for conservation management, as the research emphasises the need to understand morphological differences that could affect the fitness of endangered and threatened species being reintroduced into their natural habitats. These morphological changes could affect the reintroduced big cat’s ability to survive in the wild, explore expansive home ranges, find mates and capture food.

Associate Professor Habiba Chirchir, Marshall University, Huntington, West Virginia, USA; and, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA.

Meagan Warwick, AMRI Project and Communications Officer, Australian Museum.