A Lethal Beacon for Migrating Birds

Oil companies get prosecuted for how many birds dying in a tailings dam? Seems somewhat irrational compared to aerial cuisinarts and constructed obstacles

For the first time, researchers have now quantified this threat to birds in the United States and Canada. In a study published online in the journal PLoS One, they estimate that a whopping 6.8 million are claimed annually by tower collisions.

“Ninety-five percent of birds killed are going to be neo-tropical migrants, and many of them are birds of conservation concern,” said one of the study’s authors, Travis Longcore, the science director of the Urban Wildlands Group and an associate professor of research at the Spatial Sciences Institute at the University of Southern California.

Neotropical migrants like thrushes and warblers breed in Canada and the United States and winter in places south of the latter’s border. Most of the migrants undertake nocturnal journeys, and that’s where the trouble starts. (Daytime bird window collisions, which occur when a bird does not perceive a glass barrier, is a separate problem and not taken into account in this study.)

Scientists are not sure why nocturnally migrating birds seem to have trouble navigating around bright light sources. Some researchers hypothesize that they need a certain wavelength of light to sense the earth’s magnetic field, which they use as a compass. Others think bad weather and low cloud cover obscures the stars and may encourage birds to approach artificial light sources. Still others wonder if birds that happen upon bright light sources become entranced by the stimuli and cannot break away from that zone of influence.

In any case, birds are regularly done in by communication towers, which sometimes reach heights twice that of the Empire State Building and are anchored by miles of cable radiating around them.

To quantify the impact of the towers have on bird populations and to suggest appropriate regulatory actions, Dr. Longcore and his colleagues sought to improve on past estimates from the 1970s. The original study from that time calculated that four to five million birds are killed per year and, until now, has been the figure generally cited by agencies like the F.A.A. But Dr. Longcore and his colleagues considered that estimate to be “seriously back of the envelope” because it was based upon only three data points and assumed that every tower claimed the same number of bird lives regardless of height or location.

NYT