On the morning of Sept. 11, 1948, “a good number of dead, dying and exhausted birds” were found at the base of the WBAL radio tower in Baltimore, in what was then viewed as a new and unusual phenomenon. Ever since communication towers began popping up in the United States in the 1940s and 50s, bird bodies have littered the fields below them, especially during migration season.

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 adjunct professor at UCLA's Institute of the Environment and Sustainability.

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.

To read the full article by Rachel Nuwer click here.

Vancouver Desi, Canada's premier South Asian news portal, also covered the study. To read the article click here.

Published: Wednesday, April 25, 2012

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