This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
It's winter, and while Los Angeles has been unseasonably warm, I find my mind wandering to cooler things, like polar bears.
In most zoos and animal parks, polar bears (ursus maritimus) attract such a disproportionate amount of attention that they are referred to in the industry as "charismatic megafauna," or in other words, "really cool animals." Perhaps it is because it is especially rare for the average zoo-goer to happen upon a polar bear in the wild, or because they live in such an inhospitable environment. Perhaps it's because polar bears are impossibly cute.
Maybe we should just blame Coca-Cola.
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Whatever the reason, psychologists Michael J. Renner and and Aislinn L. Kelly of West Chester University in Pennsylvania write that because of their high level of regard they serve as "important ambassador[s] for species-survival plans and conservation efforts" and therefore have significant value in public education.
Perhaps owing to the scarcity of available resources in the wild, polar bears live most of their lives in isolation. Aside from brief encounters for mating purposes, they live and hunt alone. The longest that polar bears are known to live together is for three years while mother bears care for their cubs. Their solitary lifestyle makes social encounters between individual polar bears extremely uncommon. And yet in captivity, polar bears are housed socially, with several individuals sharing the same space. Given their size and strength, aggressive interactions between individuals could be dangerous and potentially deadly. For these reasons, it is important to understand the social behavior of polar bears, in order to best design their zoo enclosures to minimize conflict and maximize health and quality of life.
The polar bears at the Philadelphia Zoo spend their days outside sharing the same enclosure, from 9:00am to 4:30pm. Given that wild polar bears live in isolation, Renner and Kelly hypothesized that not only would social interactions between the bears be infrequent, but that they would actively display social avoidance behavior.
Two adult captive-born female polar bears, appropriately named Klondike and Coldilocks, were observed for a total of 106 hours, in 30-minute blocks, with an observation recorded every minute, over 10 months. Nothing was unique about these data collection periods in terms of the treatment or management of the bears; they maintained the same feeding schedule and enrichment programs throughout the study.
In order to record where each bear was within the enclosure at each time point, eight distinct zones were identified. In addition, any relevant zookeeper activity and the number of visitors present was recorded for each time point as well.
A total of 592 zone transitions were recorded, meaning that the bears changed positions roughly once every ten minutes. 44.3% of those movements resulted in decreasing the distance between the individuals, and 55.6% resulted in increasing the distance. However, on average, the bears were statistically more likely to move away from eachother than to move closer together. More telling, while there was only a 10% probability of one bear changing positions in any given observation, there was a 60% probability of the second bear changing positions in the subsequent minute, presumably in order to increase the distance between the two individuals.
Overall, these data support the hypothesis that Klondike and Coldilocks were avoiding eachother. In general, the bears moved farther away from each other instead of closer to each other. If one bear moved closer, the other responded by moving away to preserve the inter-individual distance.
More specifically, the bears spent only 7.2% of their time in the same zone. In slightly less than 10% of the observations in which the bears were in the same zone, aggressive behaviors were observed, which included vocalization, paw swipes, bared teeth, and biting attempts. Non-aggressive social interactions between the two bears was even less frequent. Physical contact was almost non-existent. These observations lend support to the hypothesis that the social avoidance employed by the two bears successfully helped them avoid aggressive social interactions.
How could it be that, within a relatively small enclosure, the mean change in distance between the two bears was positive? Recall that the distance between the bears increased more often than it decreased. It turns out that this enclosure is particularly well-designed: at nearly every zone within the enclosure, a path is available for moving away from any other zone. That is, each zone has multiple entry and exit points.
This is good news for zoos: if an enclosure of sufficiently complex topology is designed, polar bears can reasonably be kept in captivity with relatively low possibility of significant aggression. It should be noted that this is not a controlled experiment, but rather a case study of two bears in one zoo. It could easily be, for example, that these particular polar bears were relatively easy-going or non-aggressive. What this study does demonstrate, however, is that polar bears are capable of co-existing in the same space with low risk of aggression. As the researchers rightly conclude, thoughtful exhibit design can facilitate social avoidance behavior in solitary species, thereby improving the health and welfare of captive megafauna such as polar bears. Combined with a high-quality educational program, this can help polar bears serve as "ambassador species, increasing public awareness of important conservation issues."
Renner, M., & Kelly, A. (2006). Behavioral Decisions for Managing Social Distance and Aggression in Captive Polar Bears (Ursus maritimus) Journal of Applied Animal Welfare Science, 9 (3), 233-239 DOI: 10.1207/s15327604jaws0903_5
Photo of socially avoidant polar bear at the San Diego Zoo copyright the author.