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Stars of Navigation
Indigo buntings migrate guided by the stars. Here is the secret of how they learn the map of the sky.
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.
 I 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
 This story first appeared in the
Backyard Bird Newsletter, October, 2004.
Copyright 2004 by Diane Porter
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Can you recognize
an indigo bunting?
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