This is Bird Node. Why do birds consistently follow certain roots in their great journeys across the continents?

Tathways of migration evolved, shaped by the wind. During the height of the last ice age 18,000 years ago, much of North America was covered by glaciers,

yet ice-free breeding habitat for songbirds, such as the Black Pole Warbler, remained in what is now Alaska and parts of Western Canada.

Studies of fossil pollen found in muddy lake bottoms show that consistent winds blew across the continent on a northwest to southeast heading of 155 degrees.

As Scott Widenzalt recounts in his book, Living on the Wind, the Ice Camp produced a powerful high-pressure center sitting over central

Canada, pumping strong northwest winds precisely the conditions that would aid migrants on a

155-degree heading. The birds rode these tailwinds to traverse the vast ice fields. And today,

although the continental glaciers have melted, the birds

still follow this compass bearing on their way to wintering grounds in South and Central America

and the Caribbean. Natural selection and the vicissitudes of life on the wing require that

birds respond exquisitely to natural conditions.

Their lives depend on their attunement to the world around them,

and particularly during migration to the wind.

For Bird Note, I'm Michael Stein.