This is Bird Note. Before the high-tech gadgets used to track bird migration today, a Louisiana

ornithologist studied migration with one simple tool, a telescope aimed at the moon. George Lowry

dreamed up moon-watching in the 1940s to prove that birds regularly migrated across

the Gulf of Mexico. He knew you could see the silhouettes of migrating birds passing in front

of the full moon through a telescope. Working with an astronomer, Lowry turned moon-watching

counts into standardized measurements to compare the amount of migration at different places and times.

On a ship docked on the coast of Yucatan, Lowry pointed his telescope out over the Gulf. He calculated

that 3,700 birds crossed an imaginary one-mile line on the water every hour.

Then, in the 1950s, he organized the first continent-wide survey of migration patterns,

with thousands of volunteers across North America.

Moonwatching became obsolete once scientists began using radar to monitor migration.

But you can still point a telescope at the moon and see those flickering silhouettes of birds on the move.

Learn more about the history of bird migration research.

In Rebecca Heisman's book, Flight Paths,

how a passionate and quirky group of pioneering scientists

solve the mystery of bird migration.

For Bird Note, I'm Michael Stein.