- The Washington Times - Wednesday, March 14, 2001

The robin is one of nature's most successful dieters. A new study into the birds' feeding habits has revealed that robins have a remarkable ability to regulate their fat reserves precisely, in order to stay the same weight all their lives.

Dr. Rob Thomas, a behavioral ecologist, and his students at the University of Bristol, trained wild robins to collect food from a dish on top of an electronic balance so that they could be weighed automatically each time they fed.

It was discovered that, unlike humans who tend to overindulge when offered excessive amounts of food, robins are able to limit their food intake very precisely in order to stay the same weight.

The experiment was part of a research program to compare the daily body-mass cycle of the robins on days when they were artificially fed to when they were left to their own devices.

Dr. Thomas said: "Robins do not simply eat as much as they can to get as fat as possible. Even when food is available to them, they are not greedy. Instead they carefully regulate their food intake to avoid starving without having to carry unnecessary weight."

Each adult robin, filmed as it collected food from the dish, weighed between 18 to 24 grams. The results of the experiment showed that robins exercise exceptional self-control to avoid overeating even when faced with the tempting prospect of an endless feast of worms.

Dr. Thomas said, "The average weight difference in their body mass between days was only 0.01 grams, which is equivalent to just one or two small worms."

To survive a long cold spell of winter weather, small birds such as robins need to eat a little extra to put on fat reserves to avoid starvation. There is an art to eating just the right amount. Eating too much means more energy will be required to fly, making them slower, less agile and more at risk of being caught by the neighbor's cat. Too little and they may starve to death.

Statistically, adult robins have only a 50 percent chance of surviving into the next year. For juvenile birds, the survival rate is even lower.

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