sapote tree


Favorite Andean Bear Food: Sapote

Some of these sapote flower buds may develop into food for Andean bears, Sechuran foxes, and other wildlife.

Some of these sapote flower buds may develop into food for Andean bears, Sechuran foxes, and other wildlife.

In conservation research, we’re often interested in measuring variation across space and time, looking for patterns in that variation and deriving explanations for those patterns. However, during my last trip to the field, I found myself pondering changes over time on a much longer scale, across over 1,000 years. As I walked under the hot sun dragging a tape measure through the brush day after day, and I started stepping over ancient stone walls, it was easy to start wondering about the original purpose of the walls, even though that had nothing to do with the task at hand!

What I should have been totally focused on was making sure that we were correctly measuring the distances between trees in the tropical dry forest of northwest Peru. As part of the Andean bear conservation program, I was there working with the Spectacled Bear Conservation Society and with local citizen scientists (see post Citizen Science: Engaging People in Conservation Research). With support from the Disney Worldwide Conservation Fund, Samantha Young and I have been developing several initiatives to engage local people in conservation science and action (see Scientific Concepts for Non-scientists). One focus of my trip was to train citizen scientists in collecting data from woody plants, because we’re interested in knowing more about how plants that are important for Andean bears vary in space and time. In particular, we’re interested in understanding the variation in when and where sapote produces flowers and then fruit, because sapote fruit appears to be the critical food source for Andean bears in the dry forest of northwest Peru (see Andean Bears: A Surprising Discovery).

To get information on the sapote population, we measured little trees...

To get information on the sapote population, we measured little trees…

Although sapote is considered critically endangered, there have not been many studies done on its reproductive ecology, so we can’t simply visit a field site and estimate how much fruit the sapote trees there might produce or how many bears might be supported by those trees. So, our goal is to collect information every month, such as which trees have flowers, which trees have fruit, and the condition and size of those fruit. Because we don’t have any background information on these sapote trees, we’re going to learn something new practically every month. For example, during our first data-collection period we discovered some individual sapote with a few ripe fruit left from this past season and several new flower buds. I had no idea that the same tree might have both flowers and fruit at the same time!

...and we measured big sapote trees.

…and we measured big sapote trees.

Another new observation with more serious implications for bears and other wildlife that feed on sapote fruit is that sapote grows only in a narrow band on the lower slopes of the hills at the edge of the valleys. We knew this generally, but we had never measured the width of this strip; it’s much narrower than we thought, meaning that there’s less area covered by sapote trees than we expected, and, presumably, fewer sapote trees. Over the next several months, we’ll begin to get an idea of how many flowers and fruits those trees produce and how that production varies depending on characteristics of the sapote trees and the places where they’re living.

Although we’ll be looking at variation in flower and fruit production across relatively small-scale changes in space and time, especially in comparison to the scale of the landscape and the scale of human history in this area, these are the data we’ll need to understand variation in sapote and in Andean bear ecology.

Russ Van Horn is a scientist in the Applied Animal Ecology Division of the San Diego Zoo Institute for Conservation Research.


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.


Little Fruit, Thin Bears

This is a camera trap photo of the female Andean bear Magaly on December 7, 2009, when she was thin and in poor condition, before many ripe sapote fruit were available.

It was about 16 months ago when I first saw an Andean bear in the dry forest of Peru during the Southern Hemisphere winter. When I did, I was shocked. As this bear walked down the hillside toward a waterhole I could count her ribs, I could see her backbone, and I could watch her hipbones moving. Her fur was dull, and I could hardly believe how bad she looked. My colleagues had told me that the bears living in the dry forest were thin during the winter because there wasn’t much for them to eat, but I didn’t know the bears became THIN! The only other wild bear I have ever seen so scrawny was an American black bear I encountered many years ago in southwest Montana; that bear had become dependent on food it obtained from people, and it began starving when it no longer had access to the supplemental food.

This is a camera trap photo of the same female Andean bear, Magaly on April 29, 2011, after she’d become plump by feeding on sapote fruit.

When I expressed my concern over the skinniness of the dry forest bear to the field team of the Spectacled Bear Conservation Society (SBC), they told me that they had seen bears in the dry forest that looked even worse than the bear I was watching but that had nevertheless survived. In reality, I was shocked only because I didn’t have much experience in the dry forest; that bear was not unusual. She not only survived, but she mated a few months later and is now raising a young cub. Skinny dry forest bears look shocking to people who don’t have experience in the dry forest, but in fact their weight loss is part of a natural cycle that becomes obvious to anyone who studies dry forest bears for more than a year.

This is a portrait of nearly ripe sapote fruit still on the tree when there were ripe sapote fruits lying on the ground beneath the tree, and when bears were foraging on sapote fruits. We hypothesize that fruits like this one are critical for the survival of individual bears, and the bear population, in the dry forest.

Working with SBC in the dry forest, we’ve accumulated evidence over the last several years that Andean bear movements and body condition are linked to a species of tree, the sapote. Evidence from direct observations, camera traps, and satellite telemetry collars all suggests that bears focus their movements and foraging on sapote fruit when it is available, which is usually only for two to three months just before the annual rainy season.

After ripe sapote fruit become available, usually beginning in late November, the bears’ body condition improves noticeably, so that within a few weeks the bears no longer look like walking skeletons. After a few more weeks of feeding on sapote fruit, the bears start to look a little plump, although they never get as fat as American black bears and brown bears do in autumn. During the rest of the year when sapote fruit is not available, Andean bears in the dry forest gradually lose weight so that they are skinniest just before the sapote fruit is ripe. These observations strongly suggest that healthy populations of sapote trees are critical for the health of individual Andean bears in the dry forest and for the health of the dry forest bear population. The sapote tree is considered critically endangered by the Peruvian government, so we’re promoting conservation of sapote trees as part of the Andean bear conservation program.

A camera trap photo shows male Andean bear Russ on December 5, 2009, when he was thin and in poor condition before many ripe sapote fruits were available.

This is a camera trap photo of the same male Andean bear, Russ, on March 21, 2011, after he’d gained weight by feeding on sapote fruit.

The field team is seeing something unusual right now that may answer a question that’s been puzzling me for over a year. Young cubs and subadult bears often disappear when their mothers are skinniest, shortly before the sapote fruit ripens. We suspect that, unfortunately, when adult bears have a hard time finding food, many young bears do not survive. If that happens year after year, how can the population of bears in the dry forest remain stable? This year some sapote fruits are ripe earlier than normal, and some bears are starting to gain weight earlier than usual. This makes us hopeful that this year more cubs and subadult bears will survive. Of course, the survival of youngsters may depend on what the sapote trees do over the next few months, which reminds me of other questions we have. Why do sapote trees produce fruit when they do? What influences how many sapote fruits are produced? There has been a little research done on these questions, but we’ve still got some work to do to fill in the blanks!

Russ Van Horn is a scientist with the San Diego Zoo Institute for Conservation Research, leading our Andean bear conservation program. Read his previous post, Mountain Lions and Palm Trees.

For more information about the seasonal fluctuations in resources such as sapote and the need to conserve them, see posts Dry Forest Bears of Peru and To See a Bear.


To See a Bear

José scans the cliffs, hoping for bears.

José scans the cliffs, hoping for bears.

San Diego Zoo researchers are in Peru to study Andean (or spectacled) bears. Read a previous post, Dry-forest Bears of Peru.

It’s early morning, and the cool night air quickly burns away as the sun appears above the ridge of the mountain to the east of the camp. The light that accompanies the heat, however, reveals a spectacular scene. Still in my sleeping bag, I sit up and admire the view. Across a narrow valley, sheer cliffs drop down from the ridge and disappear below. A few somewhat gentler slopes support some vegetation. Javier points out an orange-ish post among the small trees: a posayo tree, reduced to a shattered stump by a foraging Andean (spectacled) bear.

A posayo tree is reduced to splinters by a hungry bear.

A posayo tree is reduced to splinters by a hungry bear.

Nearly six months a year, Robyn explains, bears eat these trees. Not their fruits. Not their leaves. They eat the wood. They chew them off at the base, fashioning themselves after beavers, topple the tree, and spend the next few days or weeks eating wood pulp. And pooping wood pulp.

Sapote fruit is a staple food for bears in the wet season.

Sapote fruit is a staple food for bears in the wet season.

Such are the extremes to which a dry-forest bear must go to sustain itself during the dry season. But they appear to thrive on it. How they manage to extract enough energy and nutrients from these trees is a mystery. Fortunately, bears experience more plentiful, and typical, bounty in the wet season when the sapote trees fruit. Then the bears descend to the bottom of the mountains and feed, often just a few hundred meters from human dwellings. These are the few, the essential, resources on which the bear largely depends—water holes, posayo trees, and sapote fruits. At least two of these resources place the bears in a vulnerable position, at the mercy of nearby human communities. If people were, for example, to expand their villages and farms to the base of the mountains, they may drive the bears away from the sapote trees or, worse, cut the trees down. If they brought goats or cattle to the waterholes, this too could prove disastrous for the bears and other wildlife.

cloud 9. After seeing my On cloud 9. After seeing my first wild spectacled bear, the clouds roll in, creating a surreal moment.

After seeing my first wild spectacled bear, the clouds roll in, creating a surreal moment.

Our camp is ideally situated for bear viewing. Amazingly, bears regularly descend these rock walls of the opposing cliffs to a waterhole at the bottom. This is a feat that has to be seen to be believed. All day we scan the cliffs for signs of bear. We spot a few more posayo trees that have been recently dismantled by bears. José traverses the slopes to inspect a cave where last year a female gave birth to a cub. No luck. The bears are around, but we don’t see them.

Then, just before dusk, Javier spots a dark object moving quickly down a steep rocky slope. Through my binoculars, finally, I see the bear—a large male descending headfirst, with the apparent ease of a Sunday stroll. Moments later he disappears into the bowels of the canyon where the life-giving water can be found. Tomorrow morning, we hope, we will see him ascend back up the cliffs and find a posayo tree on which to dine.

Ron Swaisgood is the director of Applied Animal Ecology for the San Diego Zoo’s Institute for Conservation Research.