Reconnect With Nature Blog

Sophisticated Tool Use In Brazilian Monkeys

Note from Con Slobodchikoff: This is a guest post by Randall Johnson, who has contributed a numer of posts to this blog and to the Dog Behavior Blog.

In a forest reserve in the savannah-like "Cerrado" biome of Central Brazil, an amazing display of planning, learning, and sophisticated tool use has been documented in a species of New World monkeys. Wild capuchin monkeys (Cebus libidinosus)— a species familiar to many as organ grinders—move along the ground, methodically tapping palm nuts that are produced at ground level to see if they are ripe. Those that pass the test are carried up into trees, where their outer cases are removed and the exposed nuts are dropped on the ground for two or three days to dry.

Then, the aged palm nuts are collected and carried to a separate nut-cracking area. There, the monkeys climb up on top of flat rocks or boulders and, using large stones they have previously selected, they start pounding the hard-shelled nuts, with the stones being used as a hammer and the boulder as an anvil.  After a few whacks, the shells are broken and the monkeys extract the kernels.

The entire process involves several days of testing, harvesting, transporting, and hammering and appears to be a planned activity—a part of the monkeys' culture—that takes place year-round.

This discovery, first reported in The American Journal of Primatology (December 2004) by a multinational research team led by Dorothy Fragaszy, a psychologist with the University of Georgia, is remarkable in that, up to that time, routine tool use in wild primates had been routinely ascribed only to chimpanzees and orangutans and, although there had been anecdotal reports of tool-using capuchins dating back to the sixteenth century, this was the first time such behavior had been scientifically documented.

Furthermore, although the stone hammers had not been fashioned in any way, their use to open encapsulated nuts is recognized as being a complex form of tool use. A number of factors (i.e., material, resistance, friability, shape, and weight) affect an object's suitability to open a hard-shelled nut, with weight being one of the most important. The heavier the object, the fewer strikes are required to crack open a nut.

Fragaszy and her colleagues originally estimated that the stone hammers weighed 16 ounces, but in a subsequent trip, they were found to weigh over two pounds. Given that adult capuchins weigh between 6-8 pounds, they were selecting—and lifting—stones a third and sometime half their own body weight.

The effective use of hammer and anvil is seen only in adults. Although juvenile capuchins are interested in the activity and often play with the procedure, they are not effective at it. It takes years of practice—and maturation—to become effective at cracking open palm nuts with the properly chosen stone.

If you would like to see a video of this extraordinary behavior, go to: http://www.youtube.com/watch?v=-G60UCeXFp0&feature=player_embedded. It's an excerpt from a BBC documentary entitled "Clever Monkey", narrated by Sir David Attenborough. In his closing remark, note his reference to these monkeys as being another intelligent species on Earth.

And if you would like to meet other animals that are known to use tools in the wild, go to: http://www.mnn.com/earth-matters/wilderness-resources/photos/15-remarkable-animals-that-use-tools/handymen

Desert Ants That Count

Note from Con Slobodchikoff: This is a post by guest author Randall Johnson, who has contributed a number of posts to this blog and to the Dog Behavior Blog.

Given that RWNB ended 2009 with a post about ants, it seemed fitting to start the New Year with another post featuring these fascinating insects.

A study done by German scientists, led by Harald Wolf, professor of neurobiology at the University of Ulm, suggests that desert-dwelling ants may have "pedometer-like" cells in their brains that enable them to count their steps and that they use this unique navigational skill to find their way back to the nest after foraging for food.

But why desert ants? Because most ants live in places that allow them to lay a scent trail on the ground that show other ants how to get to food and back home.  Scent trails, however, don't work in the desert; the constantly shifting sand scatters smells almost immediately.

So how do these ants find their way back to their nest with such unerring accuracy? It's already known that ants can use the position of the sun and the pattern of polarized light as a kind of 'celestial compass', but that doesn't explain how they determine distances with such precision.

To try to unravel this mystery, Wolf and his assistant, Matthias Whittlinger, trained two groups of Sahara desert ants to find a food site 10 meters from their nest. While the ants were busy eating, the scientists removed them and divided into three groups.

One group was left alone. The second group had pre-cut pig bristles superglued to each of their six legs, effectively giving them stilts. Ants in the third group had their lower leg segments cut off, thus making each leg shorter. (This part of the experience has since drawn some criticism. It should be noted, though, that in the wild, these segments often dry up and break off naturally without interfering with the ants' ability to walk long distances.)

The ants were then released to make their way back to the nest. The scientists watched to see what would happen. If there really was a step-counting mechanism at work, then the ants whose strides had been altered would have their calculations thrown off.

And that’s exactly what happened.  The normal ants walked right up to the nest and went inside. The stilt-leg ants, using giant steps, walked past the entrance and stopped 15 meters away. The stump-legged ants, using baby steps, stopped short of the entrance by almost 5 meters. Yet, all three groups had walked exactly the same number of steps back from the food site.

Interestingly, when the ants went out again in search of food, the two groups with altered gaits had no trouble judging the correct distance back to the nest.

Of course, this doesn't mean Sahara ants are actually counting their steps as "one, two, three, four, five," and so forth, the way we would. More likely, Wolfe explains, there is a neural mechanism at work that converts the motor excitation caused by each stride into a measure of distance.

Still, it's an ingenious solution to not being able to lay scent trails and it shows there is still much to be learned from even the humblest of creatures.