Monkeys Check the Weather to Find Food, Study Says

Nicholas Bakalar
for National Geographic News

June 19, 2006

Everyone talks about the weather, but gray-cheeked mangabey monkeys
actually do something about it, according to new research.

The African primates use their memory of the weather and knowledge of its effects on fruit and insect larvae—some of their favorite foods—to locate the ripest specimens.

Karline R. L. Janmaat and colleagues from the University of St. Andrews in Scotland followed a group of monkeys in Uganda's Kibale Forest, which sits just east of the town of Kasese (map of Uganda), from dawn to dusk for more than 200 days.

The team gathered information about how the animals' foraging habits correlated with the weather.

Using 80 target fig trees, the researchers recorded every time a group of mangabeys revisited a given tree to look for food and which trees they chose to ignore.

The team also collected data on daily temperatures and sunlight levels.

The scientists found that the average daily maximum temperature and the amount of sunshine were significantly higher on days preceding revisits.

The effects were found only for trees that bore fruit during the previous visit.

Foraging Forecast

Writing in tomorrow's issue of the journal Current Biology, the team concludes that the monkeys were taking the weather into account when they looked for food (related photos: modern weather predictions).

Warm weather not only ripens fruit but also stimulates the growth of insect larvae in unripe fruit, so visiting certain trees after a series of warm days would likely produce the tastiest results.

The amount of sunshine on the day of the foraging also affected whether the monkeys would revisit a tree, meaning it was possible that sunny days alone stimulated the monkeys to forage.

"To find out whether that was all there was to it," said Richard W. Byrne, a study co-author, "we reanalyzed the data looking only at the temperature of the days in between the last visit and the revisit. The effect held up."

The team also ruled out other sensory clues, like smell, by focusing only on the trees with unripe but insect-rich fruit. Again, the effect held up.

So, Byrne said, "we're as sure as anyone could be that the only way a monkey could know whether to head for [trees with unripe fruit with insects inside] from 50 or 100 yards [150 to 300 feet] away was by using its memory."

Overall, the mean temperature of the days between visits was the best variable for predicting the monkeys' behavior, Byrne says.

"That showed us that the monkeys were really using the weather to predict whether a revisit was worthwhile—the exciting result."

Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).