Birds in Trouble

Flying conditions over New York City one morning last week were good until about 8 a.m. Then the ceiling came down almost to the level of the Empire State Building's Observation Terrace on the 86th floor, 1,020 ft. above the street. On the floor of the terrace rained a shower of dead and dying songbirds. More than 300 (one-third of them myrtle warblers) died within half an hour after slamming against the big building. Frank Powell, who was in charge of the Observation Terrace, sent word to his friend John K. Terres of the National Audubon Society. They picked up dead birds of 18 species, including ruby-crowned kinglets, palm warblers and Empidonax flycatchers. The victims still alive were cared for tenderly.

To Naturalist Terres it was an old story. The 1,472-ft. Empire State Building, which is on the migratory flyway that leads down the U.S. East Coast, is a major obstruction to bird navigation. Migrating birds lack the dependable blind-flying instruments that enable an airplane pilot to fly with equanimity through dense clouds. Preferring to fly under a low ceiling, they often crash by hundreds against the Empire State. For some unexplained reason, they do not seem to hit mountains, and Manhattan skyscrapers almost as high as the Empire State seldom kill many birds.

Bat Mystery. On the night before the bird-crash on the Observation Terrace, two dead bats were picked up. How bats navigate over long distances is not known, but their sonar apparatus (high-frequency sound-wave ranging) generally keeps them clear of even small obstacles like twigs or wires. There are few records of bat-crashes in instrument-flying weather, but two years ago bats began to pile into the Empire State. Terres thinks that the cluster of television antennae on the building may have something to do with it. The power of the antennae has increased recently and broadcasting has continued late into the night. This may be the time when the bats fly past, and in some way the surge of electric energy flooding out of the antennae may confuse their sensitive high-frequency sound equipment.

Deadly Ceilometers. The Empire State is not the only man-made menace to migrating birds. Far worse are the ceilometer beams that measure the height of clouds above many airports. They are powerful searchlights that cast a spot of light on the base of the overcast so that an automatic instrument can calculate its height by triangulation. On migrating birds they have a terrible effect. Thousands of the birds, apparently confused by the glaring light, lose their bearings and fly into the ground or against low buildings. Last year 50,000 birds were killed in two nights at two Southern airports. Terres estimates that at least 200,000 were killed that year by airport ceilometers.

Following a suggestion from Terres, the U.S. Weather Bureau has put blue filters on ceilometer projectors at the Knoxville and Nashville, Tenn. airports. Most night migrating birds see blue light poorly. By the end of the present migration season, Terres hopes to report that his filters helped birds to reach their Southern objectives without unscheduled and fatal stops in Tennessee.

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