Spectacled Bear Breeding and Nest Building
Keeper Update, July 2009
We were pleasantly surprised, when Billie Jean, a female spectacled bear who arrived at the Zoo a few months ago, came into heat on Father's Day. Nikki, a male spectacled bear, was extremely interested in and persistent with breeding her.
Breeding season for this species is generally between April and June, during which time a female may be in heat for several consecutive days. (In Billie Jean’s case, it was five.) If Billie Jean didn’t become pregnant this time around, she may cycle again in late August or early September. Either way, because of delayed implantation (when an egg is fertilized but floats freely and doesn’t actually attach to the uterine wall until later), a birth would likely occur between mid-December and mid-January, although there have been births as late as February 28, and even a few anomalous births in spring or summer. Because of delayed implantation, these bears have a gestation period of five to eight and a half months—post-implantation embryonic development is about two months. Typically, one to three cubs are born at a time, but the most common number is two.
Billie Jean and Nikki have had visual access to each other every day since we first introduced Billie Jean to the outdoor enclosures in February. They showed quite a bit of mutual interest, peering at each other over the exhibit walls. From time to time, they’ve also been in neighboring dens with a solid door between them, and they seemed to enjoy checking out each other’s scent on their respective sides of the door. In preparation for beginning introductions, over several weeks, we regularly traded bedding and enrichment items between the two and also allowed them to explore each other’s dens so that the other’s scent would stimulate interest.
Our original plan was to gradually introduce the bears over four weeks. There would be daily mesh introductions for increasing amounts of time, followed by overnight mesh access, followed by indoor introductions (again increasing the time together each day), and finally a yard introduction. We knew that if everything went swimmingly, the entire process might take much less than four weeks. However, good general rules of zoo keeping are to “err on the side of caution,” “always plan for the unexpected” (Murphy’s Law!), and “never say never,” so it’s always best to have a good, solid, but flexible, plan in place.
On May 7 we began mesh introductions throughout the day, with keepers present to monitor the bears. We continued this for about a week and a half, and it went so well that we decided to move directly to actual introductions, rather than giving nighttime mesh access. We introduced the two inside on May 20, and that also went so well (with almost immediate affiliative behaviors such as copulation attempts and play wrestling) that after about an hour we put the bears outside together. They’ve been going out together daily ever since. To see them together you’d never know these bears hadn’t been an established pair for years. The entire introduction process took about two weeks, rather than the month that we’d planned upon.
Both Nikki and Billie Jean were brought here from other zoos at the recommendation of the Andean Bear Species Survival Plan, a subset of the Association of Zoos and Aquariums (AZA) group that tracks the genetics of AZA bear populations and makes breeding recommendations based on maintaining genetic diversity. The hope is that they will breed.
While we did see three copulation attempts on the first day that the bears were together, because breeding didn’t continue past the first day, it is likely that these were simply dominance or bonding behavior. This was not surprising to us. Given Billie Jean’s age—she turned three in December—we thought it likely that she was not yet fully reproductive and that we may not see breeding until the following year or even later. We will keep an eye on her in the coming months and keep our fingers crossed for a baby bear or two.
Spectacled bears are the closest relative of the giant panda, with which they share taxonomic similarities, including a “false thumb.” The “false thumb” and other adaptations make spectacled bears uniquely designed for climbing and navigating steep elevations. Possibly the most arboreal of all bears, and agile climbers, these bears ascend trees in search of fruit and bromeliads and, when a food-bearing branch cannot support their weight, they bend the branches to reach the food. They use broken branches and leaves to build platform-like nests in which they may spend several days awaiting the ripening of nearby fruit. Mother bears teach cubs to reach the highest, most nutritious foods and, instinctive climbers, the relatively precocious cubs begin foraging for food with their mothers within a few months of their birth.
It is not uncommon to see spectacled bears in zoos build ground nests using sticks, grasses, and other nesting materials (a natural behavior in the wild). One may also see a spectacled bear in a zoo drag materials such as hay or wood wool into a tree to nest upon. However, it is highly unusual to see a zoo bear nest building exactly as one would do in the wild. (I’ve never seen it or heard about it happening.)
The Zoo's Billie Jean is one special bear. She has built an authentic nest in one of the mulberry trees in her exhibit. She’s been known to spend hours at a time working on it. Researchers I know say it looks exactly like the nests that they’ve seen in the wild.
She began the behavior while in quarantine by piling up hay and other nesting items on top of her inside den. Once she was given yard access, keepers stood bamboo upright within her climbing structure to give her the idea of building a nest at the top. Instead, she broke it up and took it to her ground nests. Then keepers tried putting nesting materials off the ground on the climbing structure and in the crooks of trees. Billie Jean sometimes took these materials to her ground nests, but at other times began adding materials to the elevated “nests.” She eventually graduated to creating her own nests high in the mulberry trees. The one she’s been working on recently can easily be seen from the public viewing area.
Spectacled, or Andean, bears are the second largest land mammal in South America behind only the tapir, and the largest South American carnivore. Spectacled bears are the only bear native to South America. They live in the Andes and outlying mountain ranges at elevations ranging from 250 to 4,750 meters, and are confirmed to exist in five countries, from western Venezuela south to Bolivia, with possible populations in two others. Each individual spectacled bear has it own distinctive set or “fingerprint” of distinct cream or whitish markings on its head, throat and chest. Learn more.