Those who live in the country resent light pollution. After a while, we forget others live with it all the time. Neighbors with a large barn light or excessive boathouse lighting can offend us, and we will take action to reduce such unnecessary illumination, especially on a lakeshore. It doesn’t respect others’ lifestyles across the lake.

Since 9/11, New Yorkers have installed powerful twin beams of blue light that extend many thousands of feet straight up as a large memorial to that tragic event. Wonderful to see, the Tribute has become a hazard to bird-life migration on any annual anniversary of 2001. Songbirds get disoriented, flying around and about, often crashing into nearby buildings and drop dead to the ground below.

Now Cornell and New York City Audubon are doing something about this issue. Radar can depict oncoming migratory flights and alert the operators of these beams’ vertical display to shut them both off for 20 minutes until the numerous flocking birds move on. This apparently is working pretty well, with good cooperation from the authorities who have realized their visual monument is dangerous to migrants.

Other cities are becoming conscious of skyscraper lighting and informing those inhabitants to turn off their buildings’ unnecessary lighting to save birdlife at critical moments when seasonally moving down our migratory pathways. We are an urban society and must diminish our impact into the atmosphere above with this intangible pollution.

The Living Bird magazine article distinguishing this problem shows the altitudes big and small bird species fly in as they pass overhead. It is lower than previously supposed — maybe only 500 feet on the average. Swans and some others fly much higher, but the great number of passerines easily collide with buildings below that flight level. With skyscrapers climbing into the sky, we are violating the lower atmosphere.

Cornell and New York City Audubon realized this outsized vertical light represented a giant experiment in studying the effect of light in an already photopolluted urban environment. The variable illumination could literally be switched on and off. Then they could document strong evidence of the almost instantaneous benefit of turning off an intense source of artificial light.

In seven nights over nine years of study (two years were omitted due to poor weather), the lights were shut off 22 times. With each episode of temporary darkness, the birds’ behavior — including circling at decreased speeds and lower altitudes, and increased vocalization and aggression at the lights — stopped within minutes.

During nocturnal migration, many songbirds fly not in tight flocks, but loosely or singly. Periodically, they check in with each other using short, species specific flight calls. There are those that can identify warblers and other species by these sounds. Away from the lights, this can sound like a traffic jam of migrating birdlife.

Of the 102 species recorded at the site, the majority are neotropical songbirds and often the young of the past season’s reproduction. They are embarking on their first southbound migration and particularly susceptible to the dark of skyglow.

By 11 p.m., the observers are noting the count of birds in the beams is over a thousand. The birds seem to so dense they appear as a unified swirl. They cartwheel through the beams and around them, flashing like sparks.

Andrew Farnsworth of the Cornell Lab pulls out his cell phone at this level and cues up a radar image from the weather station 50 miles to the east on Long Island.

On his small screen, a stippled blue-green circle blooms on a map of New York City, demonstrating radar evidence of the birds aggregating above. Southern Manhattan becomes obscured by pixels bright and growing ever brighter. This radar reveals what the darkness otherwise conceals. And it states that many more birds are coming their way to the researchers.

If the weather on Sept. 11 is favorable for migration, the regional influence of the Tribute is tremendous. Densities of migrating birds up to 20 times (and up to 150 times) their normal levels can happen. In seven nonconsecutive nights of the yearly study of the Tribute in Light the scientists gathered below estimated that 1.1 million birds were influenced by the towering beams.

These extend skyward 4-miles skyward and can be seen out at sea. The Tribute in Light is illuminated by 88 xenon bulbs, pumping more than 7,000 watts of light into the night sky.

Building collisions claim an estimated 90,000 birds in New York City. A study by the Smithsonian Migratory Bird Center estimated that 600 million birds a year die in the United States due to building collisions, and maybe 25 million more in Canada.

The low number of bird fatalities at the Tribute speaks to the dedication of all stakeholders and the powerful impact of simply turning off the lights, allowing birds to go on.

Dave Eastman also broadcasts “Country Ecology” four times weekly over WMWV 93.5 FM. As vice president of the Lakes Region Chapter/ASNH, he welcomes you to monthly programs at the Loon Center in Moultonborough. He is available at: cebirdman@yahoo.com (or) countryecology.com.

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