Stars of Navigation

Indigo buntings migrate guided by the stars. Here is the secret of how they learn the map of the sky.

Indigo Buntings, by Debby Kaspari

On a crisp morning last week I walked to the edge of some woods where I've been watching an indigo bunting. All summer his loud song of doubled notes ("Sweet sweet, chur chur, twip twip") led my eye to a brilliant, intensely blue little bird perched at the tip of a tall tree.

This time, however, the indigo bunting was gone, as I'd half expected. Gone south, for a winter of longer, warmer days than anything Iowa can offer.

But I'm not glum. My yard is alive with new arrivals from the north, purple finches, a tiny red-breasted nuthatch, and some dark-eyed juncos. Though I haven't yet put seeds in all the usual winter spots, the juncos are already searching under the sweeping branches of the spruce, exactly where they found birdseed last March. Clearly they recognize my yard. These are my own juncos.

How did they find their way back? If I'm driving in unfamiliar territory, I need maps and road signs to guide me, and nevertheless I'm sometimes not sure whether I'm going north or south. But these little birds, with no such aids, have journeyed hundreds of miles and have returned.

No one fully understands bird migration, but we do know a few things about it. Many birds navigate by the position of the sun. Others use landmarks, such as lakes. Birds migrating by night, when sun and landmarks aren't visible, however, must rely on darker devices.

I used to wonder how baby birds entertained themselves while in their nests. Well, some of them watch the stars. Thirty years ago, Stephen Emlen, an ingenious investigator, raised some nestling indigo buntings in a planetarium. He caused the "sky" to rotate about Betelgeuse, in Orion, instead of around the Pole Star, in the north.

When the indigo buntings grew up, they tried to fly away from Betelgeuse. They behaved as if they had formed a concept of "south," as the direction opposite the part of the sky where the nightly motions of the stars formed the tightest arc.

Outdoors in nature, baby indigo buntings must spend their nestling nights learning the configurations of the starry sky. They note that the stars close to the Pole Star move the slowest of any stars in the sky, tracing the path of a small circle around that Pole Star. Henceforth the night sky becomes a map and compass for them, and it will guide them on their migrations.

Indigo Buntings male and femaleI love imagining a nest full of baby indigo buntings, peeking out from beneath their mother's warm belly to drink in the night sky. I like to think of a young bird in fall, taking its bearings from the stars as it begins its first migration. It flies to the southern border of the U.S. and crosses the Gulf of Mexico, to a land it has never seen. And the next spring, relying again on its internal astronomy, it will return, I trust, to sing a bright song of doubled notes from a treetop at the edge of the woods near a small town in Iowa.

-- Diane Cooledge Porter

Diane PorterThis story first appeared in the Backyard Bird Newsletter, October, 2004.
Copyright 2004 by Diane Porter



Indigo Buntings

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