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Why was a bear following an anteater through Peru’s mountains?

San Diego Zoo scientists often come back from the field with wonderful tales of their adventures and interesting findings. One of the zoo’s newer programs is about Andean (spectacled) bears in the cloud forests of southeastern Peru, near the route of the Interoceanic Highway that is under construction.

Russ Van Horn works with biologists in Peru and local villagers to help study the Andean bear. He has set up camera traps to capture wildlife, especially the bear. Not a lot of research has been done on this species, so Van Horn’s study is gaining valuable information, including documentation of a bear following a giant anteater.

By Russ Van Horn

Andes Mountains, Peru–The longer we have remote cameras deployed in the forests on the eastern slope of the Andes in southern Perú, the more questions I have about what is going on in those forests. Each camera has been programmed to take 10 photos in rapid sequence as soon as it detects motion, and one of the cameras took a sequence that I find simply amazing.

The first few photos show a giant anteater walking up the trail, which is not uncommon at that camera station, 2.1 kilometers [1.3 miles] off the Interoceanic Highway at 1273 meters [4,200 feet] elevation in primary forest. As the anteater, known in Spanish as an oso hormiguero, walked out of sight below the camera, the shine of two eyes became visible in the distance.

When I first saw those eyes in the photo, I assumed that they were the eyes of another anteater. However, in fact they were the eyes of another oso, an oso andino, or Andean (spectacled) bear. This bear was walking up the trail, 3-5 meters [10-16 feet] behind the giant anteater.

Both animals are partially visible in one photo, so it was not a case of the camera failing to record the correct time for the photos of the Andean bear; the two animals actually were in the same place at the same time.


A remote camera photo taken on 21 July 2010, showing a giant anteater walking up a trail.


A remote camera photo taken on 21 July 2010, showing the tail of a giant anteater and the eyes of an Andean bear.


A remote camera photo taken on 21 July 2010, showing an Andean bear following behind the giant anteater.


A remote camera photo taken on 21 July 2010, showing an Andean bear following behind the giant anteater.

Photos courtesy of San Diego Zoo

I could calculate the probability that this would happen simply by chance, but I don’t think I need to–the probability would be so small that I’m confident it’s not a coincidence. So, what was the Andean bear doing there, and then?

Other than coincidence, I can think of two hypotheses to explain why the animals were together.

First, there is the possibility that the Andean bear was hunting the giant anteater. However, I think this is unlikely, for three reasons.

  • Based on the analysis of their feces, and the evidence they leave in the forest, Andean bears are thought to be primarily vegetarian.
  • The posture of the giant anteater was not obviously any different than in any other photos, so although it had to be aware that it was being followed, there wasn’t any visual evidence that it was alarmed by the bear.
  • Giant anteaters have strong forelimbs and claws, and I don’t think they would be easy prey for a bear.

“So, if the Andean bear wasn’t hunting the giant anteater, what was going on?”

So, if the Andean bear wasn’t hunting the giant anteater, what was going on?

I think my second hypothesis is plausible; I think the Andean bear may have been following the giant anteater to benefit from the anteater’s superior ability to find and excavate colonies of social insects, such as ants. In other words, the bear may have been acting as a type of parasite, waiting for the anteater to find food that it could pilfer.

Peruvian bear facts.jpg

I don’t have any data to test the predictions of this hypothesis, I haven’t found any records of this behavior in the scientific literature, and none of the bear biologists I’ve asked has seen this type of behavior before. For now, it’s still a mystery as to why there were two types of bears in one photo.

Andean bears (Tremarctos ornatus) are considered vulnerable to extinction by the IUCN, due to rapid loss of habitat and corresponding decline in bear populations. It has been estimated that 50 percent of the remaining habitat for the bears exists in Perú and Bolivia, but this estimate was generated decades ago based on assumptions that have not been thoroughly tested.

In reality, most of the accepted knowledge about Andean bears is based on limited data that may not apply across the bears’ distribution from Venezuela to Bolivia. The goal of the San Diego Zoo’s Andean bear conservation research program is to address the gaps in our scientific knowledge relating to conservation questions in Perú, while providing opportunities for Peruvian students and biologists.

We’re investigating the bear not only for its own sake, and because of its impact on plants through consumption and seed dispersal, but also because of its role in indigenous and post colonial human cultures. People care about the bear, and are essential for its conservation, so it acts as a flagship species for the mountainous forests in which it lives.

Because it is difficult to use more traditional methods of investigation to collect data on bears living in the closed montane forests, we’re collecting much of our data through a system of remote cameras (a.k.a., camera traps).

Because the bears have individually distinct facial markings, we should be able to estimate the number of bears photographed, and collect preliminary data on bear behavior and demography.

In addition, we’re using remote cameras to collect data on the mammalian diversity in these poorly studied forests, in an area that is undergoing rapid increases in human population and diversification in human economic interests due to the construction of the Interoceanic Highway from the Atlantic coast of Brazil to the Pacific coast of Perú.

Dr. Russ Van Horn serves the San Diego Zoo’s Institute for Conservation Research as senior researcher with the Applied Animal Ecology Division. He is primarily engaged in developing and implementing a conservation science program aimed at conserving Andean (spectacled) bears and their forested habitats in Peru. With degrees from the University of Minnesota, Montana State University, and Michigan State University, Van Horn has authored or co-authored 20 scientific articles and has given over 25 scientific and public presentations. He is a member of the American Society of Mammalogists, the Animal Behavior Society, the International Association for Bear Research and Management, the International Society for Behavioral Ecology, and the Society for Conservation Biology.