Building Bird Strike Study

Tim Keyes
Nongame-Endangered Wildlife Program

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It has long been known that birds collide with man-made structures (buildings, communication towers and power lines), particularly while migrating in bad weather.  Some studies estimate that between 700 million and 1 billion birds are killed annually by these collisions.  Several studies of single buildings in Atlanta have been published in The Oriole, but no broad scale effort to determine the city-wide extent of bird collisions had been attempted.

This past migration season, we assisted Lee Sexton, a graduate student from the University of Glamorgan (U.K.) to address this issue in Atlanta.  Lee worked with 8 volunteers to monitor more than 50 buildings in Downtown, Midtown, Buckhead and along the Chattahoochee River.  The study began in early August and ended on October 10.  Each building was visited every other day throughout this period.  Birds that were found were identified, aged and sexed.  As we analyze this data, we hope to get some insight into which buildings are more problematic based upon height, reflective surface, and location. 

Every building visited had some avian mortality associated with it, but some buildings were far worse than others. Our worst building had 22 mortalities. Our total count was 331 birds of 54 species.  Most heavily represented were Tennessee Warblers (38), Ruby-throated Hummingbirds (35) and Ovenbirds (24). Some resident birds were found, including House Finches, House Sparrows, European Starling and Northern Mockingbirds, but these were in very low numbers compared to migrants.  Several birds of interest included Golden-winged Warbler, Blue-winged Warbler, Wilsons Warbler, Sora, and Green Heron.

Though it was often difficult to determine the timing of strikes, our impression is that many, if not most, of the strikes documented were day-time strikes occurring after migrants had settled in a vegetated area after a nights flight.  These strikes occurred where trees and shrubs were found adjacent to reflective glass, and where lobbies had inside potted trees and shrubs visible from the outside.

We documented nocturnal strikes as well, which generally occur when birds are forced to fly low due to bad weather. Brightly lit buildings seem to confuse migrants, trapping them in the bright light, which they are reluctant to fly out of, until they are exhausted or collide with a building. As previous studies have documented, our worst nights for bird strikes occurred when northerly winds coincided with low cloud cover.

These two types of strikes require different responses.  Making ground-level glass more visible to birds may decrease daytime strikes.  Falcon cutouts or other devices that make a pane of glass visible to birds may help. Removing or obscuring plants inside lobbies should also reduce bird strikes.  If bird feeders are used, placing them close to windows (within 1 meter) decreases the speed of collisions, and leads to less mortality.  Turning off building lights at night (11PM until dawn) is an effective measure to reduce nocturnal strikes.  Cities such as Chicago and Toronto have successfully initiated Lights-out programs and have documented significant reductions in avian mortality. This is a sensible way to both conserve energy, and reduce our impact on migratory birds.