‘Moon watching’ helpful in counting of birds

Certain spring nights are perfect for witnessing the migration of birds. I’ve been out during the dark hours recently and heard the call notes of songbirds as they passed, invisible, overhead. This never fails to fill me with wonder and awe.

During the most recent lunar eclipse, I was treated to an especially memorable occurrence.

I had read that the moon sometimes takes on a rusty red color at certain points of the earth’s passage across its face, and this would be more visible through binoculars or a telescope. So I stood outside at around 3 a.m., watching the last phases of the eclipse, and decided to scan the moon’s sphere of light for migrating birds

At first, there was nothing. After perhaps five minutes, I saw the small silhouette of a bird as it zipped across the globe. Gooseflesh broke out on my skin. I waited excitedly to see another as I absorbed the sights, scents, and blessed absence of noise of that predawn early morning.

The moon glowed with a muted ruddy light, seeming to be lit from within. The air, moisture-laden with the evaporation of the previous day’s rain, smelled sharp and sweet. The soothing quietness was almost permeable.

Presently I saw five more forms flit across the moon. These birds were not flying very high, of course – otherwise they would pass beyond the limit of visibility. But when they happened to fly within that section of sky lit by moonlight, they were briefly visible as silhouettes.

Birders and scientists have been observing nocturnal migration in this way for many years. This simple method of “moon watching” has yielded scientific approximations of the number of birds passing overhead per hour.

A more technical and complex, but no less exciting, method has begun to be used extensively – radar. In the book “Gatherings of Angels,” Kenneth P. Able recounts what early radar operators thought of the expanding images on their screens. Never guessing that they were caused by migrating birds, they called them “angels.”

“Indeed,” Able writes, “there is something almost miraculous about their explosive appearance just after dark as the woods, fields, marshes, and mud flats disgorge their avian contents into the night sky. The numbers are sometimes nearly incredible, hundreds of thousands of individual birds crossing a line one mile long every hour for most of the night.”

I searched the Web for radar images of such extraordinary events, and found a page on the New Jersey Audubon Society Web site (New Jersey is my home state). The image depicts an incredible fall migration on Sept. 25, 2001, accompanied by a short narrative. There are also sonograms of bird flight calls recorded at flight call detection stations. These have also provided invaluable information on the numbers and kinds of birds aloft at night during migration. The web address is: http://www.njaudubon.org/education/oases/scenario.html.

Enjoy!

Chris Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com