In February 2005 nine members of the Evanston North Shore Bird Club were boating to the idyllic Sapodilla Cayes, 40 miles due east of Punta Gorda Town in Belize when we saw a hapless Kentucky warbler plop onto the sea in front of us. We plucked him to safety, placed a few drops of fresh water on his beak, and released him onto a palm frond. We hoped to see him in May in Evanston.

Many of “our” nesting birds winter south of the Tropic Cancer in the Western Hemisphere, in the biogeographical region known as the “neotropics.” They migrate north to breed. Birds who have flown across miles of land and water spy Montrose Point jutting invitingly out into Lake Michigan, or Gillson Park in Wilmette, or Evanston back yards as promising stops for nourishment and rest.

Birds appear in the fossil record around 150 million years ago in the Jurassic period. Doug Stotz of the Field Museum says our modern birds date back to around a million years ago. Current migration patterns date back to the end of the last ice age around 10,000 years ago.

Forces triggering migration are poorly understood. Researchers, however, have tentatively established that changes in light and day length stimulate physiological changes in birds’ brains and hormones while on their wintering grounds, causing them to be hungrier and bulk up with fat. The fat fuels the contracting flight muscles, allowing long flights with little fatigue. Most species stop periodically to refuel. The tiny ruby-throated hummingbird, a favorite visitor to bluebells and red flowers, flies nonstop 600 miles in 24 hours over the Gulf of Mexico, its wing beats averaging 70 times per second. It is unimaginable.

Typically, raptors soar during the day, catching thermals over landforms, and songbirds migrate at night. The sun probably plays a primary role in guiding migration routes. Cloudy days can disorient some species. Stars, the earth’s magnetic field, landmarks and wind direction, as well as some genetic properties, also provide cues. Heavy storms and wind directions that alter with high and low pressure systems may throw birds off course.

Joel Greenberg, in “A Natural History of the Chicago Region,” recounts a day when two days of southerly winds had brought waves of northbound migrants. The rain began, and the winds were still blowing, and “birds literally descended from the sky. In Chicago, thrushes, common yellowthroats, gray catbirds, and white-throated sparrows were so numerous that nonbirders called newspapers in wonderment. … In Northwest Lake County, Ind., … front lawns seethed with warblers: yellow-rumped, yellow, cerulean, black-and-white, and others. … [T]hese usually arboreal species (which create eyestrain on the neck while the watcher is looking up), were feeding on the ground.”

When birds arrive in the big city after surviving a multitude of hazards, man-made perils await them. Lights from tall buildings are particular threats, because birds are attracted to light. Once attracted to a lighted building, they become confused and often fly around crazily, bumping into clear windows that reflect what look like life-saving trees. Morning after morning during migration, volunteers retrieve dead birds and deliver the injured to rehabilitation centers.

According to the Chicago Department of Environment, “Depending on the weather, tens of thousands of birds can fly over Chicago in a single night. As some building owners know, a hundred birds might be killed at one building on a night of heavy migration.”

In 2000 Chicago adopted a lights-out program. Toronto, New York, Detroit, Minneapolis and Boston use the same strategy. Building owners and managers voluntarily turn off exterior decorative lighting after 11 p.m. during migratory seasons, from March 17 until June 7 and from August 25 until October 25, saving hundreds of avian lives. Even short buildings along the lakefront can benefit birds by using task lighting and blinds during migration.  To learn more, google “Lights Out Chicago.”

Given the Environmental Sustainability section of Evanston’s Strategic Plan to “protect and optimize the City’s natural resources,” it would be entirely appropriate to take migrating birds into account and become an extension of Lights Out Chicago.  What is needed to be a truly “Green City” is the recognition that birds are one of our most precious and beautiful natural resources.

Libby Hill

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.