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.
This seems to be a baffling dilemma. Why don’t the female bears eat more sapote fruit? What else do they seem to eat? Are they healthy? Do they give birth to healthy cubs? Is there something else in their enviroment that is preventing them from eating more?
You certainly have your hands full figuring out a lot more about the Andean bears. Best of luck and keep us posted.
Thanks for your questions on this puzzle. We don’t know yet why individual bears don’t spend more of their time eating sapote, but one of our hypotheses is that their stomachs simply fill up, and they have to wait for their digestive systems to empty. Many animals can eat large amounts of food when it’s available, but the bears in this population don’t often have surplus food, so maybe the change is just too large and too rapid for their systems.
We don’t know of anything in the environment that could keep them from eating more. When there are sapote fruits available, that’s what they eat. At other times of year, bears in this population basically eat whatever’s available: other fruits, which are smaller and rarer, bromeliads, snails, and the wood of the pasallo tree. The bears generally appear healthy, although their body condition changes seasonally.
It’s tough to find the bears’ dens, so we don’t have much data on young cubs, but they appear to be born healthy. Available evidence suggests that there’s low survival to adulthood in this population, but we think that’s linked to the seasonality of sapote fruiting and not to the bears’ behavior.
You can read my post, Little Fruit, Thin Bears, for more on this topic.
Russ, Thanks for the information. I read your previous post “Little Fruit, Thin Bears” and was shocked at the amazing before and after photos of those two bears. It’s incredible that their bodies can handle this feast and famine scenario. I’ll be looking forward to more on your studies on the Andean bears. I hope that your team can help prevent some of deaths of the young bears.
One of my tasks this trip was to work out semi-objective methods for assessing fluctuations in body condition of bears from photographs, and then review the camera trap photos from the dry forest. It’s still shocking to me to see how thin these individuals get, and amazing to see them in front of the cameras again a few months later, looking great (although never fat).