Warming climate, shrinking birds

Researchers found that tree swallows have gotten about 3% smaller over the last 30 years as the climate has warmed. Credit: Cephas

As the climate warms, North American birds are becoming smaller. In a study published in Nature Ecology and Evolution, researchers from the University of California, Los Angeles found that over the past 30 years, the average bird’s body mass dropped about .6%. Tiny tree swallows (Tachycineta bicolor), saw the greatest change, with their body mass dropping nearly 3%. “If you’re a larger person and you’re in a cold environment and let’s say you have a very small friend, you will probably be able to withstand the cold a little bit better than a smaller person would,” lead author Casey Youngflesh told Live Science. “This really comes down to surface area and volume. As a larger person, you’ll be losing less heat than a smaller person. The same thing applies to birds.”

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