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bear researcher

18

Andean Bears: A Surprising Discovery

A member of our collaborative field team watches a cliff for bear activity.

This summer my colleague Megan Owen and I were fortunate enough to have an intern working with us. Michael Forney was the John E. and Dorothy D. Helm Summer Fellow, working in our Applied Animal Ecology Division (see Summer Intern Enjoys Opportunities). He extracted behavioral data from videos of wild Andean, or spectacled, bears, living in the tropical dry forest of northwest Peru, where we work with the Spectacled Bear Conservation Society. Some of the videos were collected opportunistically by the field team, when they unexpectedly encountered a bear, and other videos were collected on a more systematic basis. There are more videos yet to review, but the preliminary results are pretty interesting.

These were the first behavioral data ever collected on wild Andean bears, and they delivered some surprises. For example, for most of the year the bears appear to lose weight, suggesting that there’s not enough food available. However, during the period of time when sapote fruit is available, the bears feed primarily on those fruits and appear to gain weight. We’d already seen this pattern, from different sources of data; however, Michael’s results suggest that dry forest Andean bears do not respond behaviorally to a feast and famine cycle like Northern Hemisphere bears would.

Sapote fruit: Does it dictate bear activity?

You may already know that American black bears and brown bears really focus on foraging during the period before they hibernate. Generally, these black and brown bears are driven to fatten up before the months when they won’t eat, so they spend as much time eating as possible. If Andean bears in the dry forest, which don’t hibernate but which do spend months with little food, behaved like these other bears, then you’d expect the bears in the videos to spend most of their time eating sapote fruit during the relatively brief period when it was available. However, Michael’s data show that adult females, with or without cubs, spend relatively little time eating, even when there appears to be a surplus of sapote fruit.

Why don’t these females spend more time feeding? We’ve generated a few hypotheses to address this question, but confirming this phenomenon and testing these hypotheses will require more data from more videos.

This is not just an abstract academic question, without relevance for the conservation of these bears. If weight gain among female Andean bears in the dry forest is constrained by sapote fruit availability, then perhaps an increase in the number of sapote trees would improve the body condition of the bears. However, if weight gain among these females is constrained by something else in addition to food availability, as might be suggested by Michael’s data, then increasing the number of sapote trees would not improve the bears’ body condition. Michael’s work reminds us that we have a lot to learn about Andean bears to further their conservation.

Unfortunately, we’ll have to pursue this question without Michael’s help, as he’s finished his internship with us and has gone south to put his talents to work in Ecuador. Thanks, Michael, and good luck!

Russ Van Horn is a scientist in the Applied Animal Ecology Division of the San Diego Zoo Institute for Conservation Research. Read his previous post, Peru: Conservation Science at Local Level.

43

Bears in Winter

As we head into the winter months of the Northern Hemisphere, bears across the globe are preparing for a change in weather. But not all bears respond to the season in the same way.

Wild brown and black bears are facing a bleak time of limited food availability in the coldest months of the year. For this reason, late in fall they engage in hyperphagia, compulsively eating anything they can get their paws on. This builds layers of fat that will be essential to keeping them warm and healthy through the upcoming winter. 

This fat is not only insulation against the cold, but the key to their ability to hibernate. While in their winter torpor, the bears draw on fat to keep their metabolism running, thus minimizing the wastage of their muscle while they fast. Adult female bears need an especially good store of fat to support the energetically demanding processes of birth and lactation while denned up over the winter months.

Pandas are Northern Hemisphere bears, but they do not experience torpor to the same degree as their North American cousins. Unlike the salmon, berries, and roots depended upon by brown and black bears, bamboo does not typically experience seasonal fluctuations in abundance. Only panda females den up, and the timing of their denning seems to coincide with the shooting of bamboo in some areas, making a more nutritious resource available at a time when a new mother needs it most. But the panda males do not experience torpor; they continue eating year-round.

Polar bear females den up in late fall and give birth in November or December. They emerge in the spring. But males don’t den up extensively; instead, the winter is an active time for the males, as the sea ice returns and they can break their fast by hunting on the ice.

Some zoos manage their animals differently, promoting the cycle of hyperphagia and torpor that exists in the wild. At the San Diego Zoo, our cold-weather bears don’t experience the same seasonal food variation as do their wild counterparts. This is why grizzly bear brothers Scout and Montana won’t spend their winter months waiting out the cooler weather; instead, they will be active year-round. Our polar bears, too, don’t have to worry about ice abundance, because the staff supplies them with year-round sustenance. Only our pandas will demonstrate a pattern of behavior typical of their wild counterparts in the Northern Hemisphere.

Of course, it’s a well-known truism around the panda facility: you can always count on Gao Gao to show interest in his bamboo, no matter what or where we are on the calendar.

Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Panda Family Reunion?