Are Pigeons Getting Fatter?

The state of the universe.
April 17 2012 8:10 PM

Big Bird

Are New York’s pigeons getting fatter? An investigation into animal obesity.

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What did Alberts have to say about my fat pigeon? Did she think the global population of fat animals had reached an all-time high? She wasn’t sure. “If you went back to Egypt 5,000 years ago where they had lots of grain stored in granaries you can bet they had fat cats and fat mice and fat dogs.” But, she noted, “[W]herever there is excess human food, and humans have commensals, those commensals are going to be able to get fat.”

It might seem that birds shouldn’t get fat because they have to fly, but that is not the case. Many migratory birds get supremely blubbery in the days leading up to their big trip—some to 70 percent body fat. Adipose tissue weighs less than muscle, but it carries more energy, making it an essential resource for a long-distance flight. Pigeons don’t migrate, though, and despite their seasonal weight gain, birds tend not to be among the world’s top fatties. Research by the British zoologist Caroline Pond, author of The Fats of Life, suggests that human beings are among the bigger lard-asses in the animal kingdom, neck in neck with notable porkers like the hedgehog, the polar bear and the great whales, the fattest of God’s creatures. (The whole point of whaling was to get at their lipids.) In general carnivores tend to be more prone to growing chubby, as fatness is an adaptation to an unpredictable food supply.

Pond may be the world’s leading scholar of fat animals. Beginning in the early 1980s, she began riding her bike around the woodlands near her U.K. home at night collecting all the road kill she could carry: hedgehogs, badgers, foxes, whatever turned up stiff. Zookeepers and farmers gave her corpses, too—camels, monkeys, brown bears, whales—and soon she had dissected more than 250 mammals. Her interest was the comparative distribution of adipose tissue, a topic most life scientists at the time were too dignified to tackle. In mammals fat depots surround most organs, but textbooks often showed them with the fat removed, as if it were not part of the biological picture. What did Pond think about my fat-pigeon investigation? How was she preparing for the Age of Fat Pigeons? Well, she didn’t really think pigeons got fat.

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Pigeon experts agree. Courtney Humphries, author of the book Superdove: How the Pigeon Took Manhattan ... and the World, said she hadn’t heard of a pigeon obesity epidemic. Daniel Sol, a pigeon researcher in Spain, brought my fat pigeon flight of fancy crashing to Earth in an email: “Even in captivity, where food is not limiting, feral pigeons do not tend to get fat.” He said Montreal pigeons are bigger than Barcelona pigeons, even though Montreal pigeons have less food. He guessed the difference was due to the Canadian cold. Karen Purcell with Cornell’s Project PigeonWatch suggested the fat pigeon I saw might have been fluffing out its feathers because it was chilly. Urban bird expert John Marzluff wondered if the fat pigeon I saw might have been a dominant male—a big stud. He did allow that my vision of the fat pigeon eating a Big Mac was not crazy, based on his work in crows. “Oh, they love Big Macs, French fries and Cheetos and hot dogs. Corn dogs are especially a favorite.” But urban birds don’t seem to get fat. Too many hawks and other birds to worry about. As the animal philosopher Rikki-Tikki-Tavi once observed, “a full meal makes a slow mongoose.”

So my fat pigeon was a phantom. The obesity epidemic had not escaped captivity—it had colonized my mind. And if I ever see that pigeon again, I know what I will say: It was wrong of me to call you fat.

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