Review examines how birds can stay thin even when they eat too much

Recognizing that songbirds, such as finches, do not appear to be growing in spite of overfeeding feeders, London environmental biologist Lewis Halsey wondered if the amount of energy birds were singing, shuffling, or exercising. to regulate their weight. In a review of literature published September 18 in the journal Trends in ecology and evolutionhe explores whether songbirds do not have to worry about their number of calories because they can control how their body uses energy.

"The bird feeders near my home never seem to get fat despite the constant availability of this buffet, but there are people who become heavy when they are exposed to this kind of food at will," says Halsey. (@lewis_halsey), from the University of Roehampton. "I wanted to study the possible behavioral and physiological mechanisms, apart from the foods eaten and the complete physical exercises, which help the animals to control their energy budget and their body weight.

Now, we may never see large songbirds, because those who gain too much weight are caught by a series of predators. However, this predation pressure would eventually eliminate the evolution of this trend, and recent studies indirectly suggest that birds are able to balance energy intake by increasing their daily metabolic rate or decreasing the Efficiency with which they can extract energy from ingested food. .

"For a given amount of food, an animal may unconsciously adjust its energy efficiency, for example by changing the frequency of wing beats or singing patterns to use more or less energy, or physiologically, by digestive or cellular metabolism. "Efficacy," says Halsey.

Based on emerging evidence, he wants to reframe the way we think about the standard equation subtracting the energy consumed from the energy burned. "We must remember that" the energy in "is not what is pushed into the beak, but what is absorbed in the intestines and what the cells extract." And that goes for the humans and other animals, not just songbirds. "

Halsey has pointed out some areas of additional research. Such an experiment could present birds that normally stay thin in front of a seed-filled bird feeder with a more appealing and easier-to-digest option. "I want to give birds the equivalent of ice cream and see if that breaks their determination and the fine control of their body mass, as it happens in many humans, or even in the face of ice cream, the birds are steadfastly maintaining their weight, "he says." This could be done in a preliminary lab and later on in the field to help us understand how these underlying mechanisms regulate body weight. "

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More information:
Lewis G. Halsey, Stay thin when food is plentiful: What energy mechanisms might be at stake? Trends in ecology and evolution (2018). DOI: 10.1016 / j.tree.2018.08.004