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Why songbirds can overeat and not get fat

Sept. 18 (UPI) — Songbirds living near bird feeders have access to an unlimited supply of food, and yet, they never seem to gain weight.

According to research published this week in the journal Trends in Ecology and Evolution, instead of precisely controlling food intake, songbirds may be able to adjust the way their bodies use energy.

“The passerine birds at the bird feeders near my home never seem to get fat despite having this buffet constantly available to them, but there are people who get heavy when exposed to that kind of all-you-can-eat environment,” Lewis Halsey, an environmental biologist at the University of Roehampton, said in a news release.

Halsey argues there is more to weight control than calorie intake. Birds with access to bird feeders may increase their exercise by singing more involved songs or flapping their wings faster. Birds may simply fidget more frequently.

Birds may also be able to control how much energy is derived from food.

“Physiological mechanisms could include reducing digestive efficiency or mitochondrial efficiency,” Halsey wrote in his newly published paper.

The newly published paper is an option article, but Halsey hopes to conduct controlled experiments in the near future. Halsey wrote the article in order to reframe the way scientists think about weight management.

“We need to remember that ‘energy in’ isn’t what’s shoved down the beak but what’s taken up through the gut and then what’s extracted by the cells; looking at it as just the amount of food consumed is too simplistic,” Halsey said. “And this goes for humans and other animals, not just songbirds.”

First, Halsey wants to find out if the contents of bird feeders help explain birds ability to maintain their weight. Even the hungriest humans would have trouble overeating if only supplied with healthy whole foods — nuts and vegetables, for example.

“I want to give birds the equivalent of ice cream and see if that breaks their resolve and fine body mass control as it does for many humans, or if, even in the face of the ice cream equivalent, whatever that might be, the birds resolutely maintain their weight,” Halsey says. “This could be done in the lab preliminarily and later in the field to help us understand how these underlying mechanisms regulate body weight.”

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