Home on the (Home) Range

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Keeper Kathy with Yun Zi

Over the next few weeks, we will be transitioning little Yun Zi and his mother to another part of the San Diego Zoo’s Giant Panda Research Station. The pair will cross through tunnels, and Yun Zi will encounter new sights and scents along the way. Some of these will be from his siblings, Su Lin and Zhen Zhen. This will all be interesting to him, and we will probably see increased olfactory activity in both mother and cub. However, encountering the scent of other bears, even relatives, wouldn’t be unusual for a panda in the wild.

In the bamboo forests of China, pandas inhabit home ranges rather than territories. A territory is typically a home space that is defended by its owner. Territorial animals, like wolves, hummingbirds, and gibbons, defend a reasonably small area in which an important resource is concentrated. Food, mates, and nesting sites are typical resources that may promote territoriality, depending on their availability. Being territorial is energetically expensive, as defense of one’s territory requires vigilance, advertising of your willingness to defend your space, and sometimes injury from fighting. As a result, only a small proportion of animals are territorial.

A home range, by contrast, is an area inhabited by an animal that is not defended against conspecifics. Animals whose important resources are evenly distributed throughout its habitat often develop home ranges, and because food or nesting sites are abundant, they need not expend energy excluding others from the area. Pandas live in home ranges, and their bamboo food source is, ideally, found all around them as they traverse their terrain. The panda doesn’t expend any energy in defending its home range, which is good: bamboo doesn’t pack an energetic wallop for those who eat it.

How big is a panda home range? George Schaller studied wild pandas 30 years ago and described home ranges for females of about 4.5 square kilometers (1.7 square miles). Males’ home ranges were larger, about 6.1 square kilometers (2.3 square miles). But we’ll have to see if these numbers hold. Our recent collaborative work with colleagues in China has documented the movement of one female who traveled 50 kilometers (31 miles) during the breeding season, two years in a row. Is this an anomaly, or does this suggest something more we don’t yet know about the fluidity of panda home ranges? We’ll have to wait and see how the data comes in.

Home ranges of different individuals may overlap, as in the case of the panda. Our research has shown that, at least in some cases, female youngsters are the ones to leave their natal home range not long after weaning. So far, we haven’t seen the same movement from young males. With this dynamic, relatives across generations may wind up as neighbors over the years, and the scents they leave behind will be picked up by other bears as they make their way through their home ranges.

As Yun Zi transitions to our main viewing area, he will experience for the first time some of the other residents of our facility. Bai Yun, for her part, is very familiar with the main exhibit spaces and the scents of these other bears. It is tempting to liken their experience to that of a mother-cub pair in their wild home range, moving out of their core area and crossing over the paths of other bears who have been nearby recently. Although our pandas’ environment is not a wild one, we can be assured that what they are about to encounter is a familiar situation for their species.

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.