Molting is the way birds freshen their feathers

  • Updated: December 3, 2013 - 2:27 PM

The birds you see at your feeder might sport a different look.

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American goldfinches show molt as well as any of our local birds. The males lose their bright black and yellow plumage in the fall, replacing it with drab colors. They regain their glory in the spring, when looking good for mate competition is important. This male shows the winter plumage.

Photo: Photos by Jim Williams • Special to the Star Tribune.,

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“Molt,” said my friend Ashley, “sounds dull.”

.We were talking about this column, and my effort to make bird molt interesting.

“Molt doesn’t sound interesting,” she said.

“Well, you don’t know anything about molt,” I said.

“Birds molting is sort of like women shopping for clothes,” I said. “Some women buy new clothes spring and fall. Some are always buying. On some women you notice the change. Other women always look the same.

“That roughly describes molting in its various forms.”

Ashley, who molts stylishly season-to-season, looked skeptical.

“You’ve seen a loon, right,” I asked, “watched them run across the water to take flight?”

“I think so,” Ashley said, who looks like a city girl.

Well, I said, loons molt their primary flight feathers all at once: Boom, they go flightless until new feathers are in place.

“Sounds extreme,” she said.

“Yes,” I said, “but there’s a reason.

“Loons are birds with unusually heavy bones, for birds. Loons eat fish, so they need weight to make diving efficient.

“The birds must accommodate both diving and flight. The extra weight creates a high wing-load ratio. But fly they must, so loons run across the water, slap, slap, slap, to acquire the air speed needed for liftoff.

“Take away a primary feather or two and flight becomes difficult, maybe impossible,” I said. ”So, loons make wholesale replacement of those feathers when they reach their ocean wintering sites.”

“Wait,” Ashley said. “What’s wing-load ratio?”

“Oh. It’s the amount of weight each square inch of wing surface must carry. Chickadees, tiny guys that weigh almost nothing, have a ratio that’s 10 percent that of loons,” I said.

“So, loons run like hell to get airborne while chickadees pop into the air.

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