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Wildlife-friendly yards increase risk of bird–window collisions

White-breasted Nuthatch is a species at risk of window collisions.
White-breasted Nuthatch by Michael Travis.

The number of birds killed in collisions with windows in the United States is staggering.

In 2014, researchers Scott Loss, Sara Loss, and Peter Marra of the Smithsonian Migratory Bird Center and Tom Will of USFWS Division of Migratory Birds estimated the toll to be between 365 million and 988 million birds every year.

The investigators reported that high-rises, buildings at least 12 stories tall, kill more birds per building than detached houses or multi-unit residences 1-3 stories tall, but that residences vastly outnumber high-rises. Consequently, reducing mortality significantly will require mitigation measures to be applied across a huge number of structures.

And that presents a problem, because until now, we haven’t been able to say exactly which types of houses and what types of windows are most problematic.

To address this shortcoming, researcher Justine Kummer of the University of Alberta and colleagues from the university and Canadian Wildlife Service asked Alberta homeowners to monitor their properties daily for evidence of bird–window collisions. Then Kummer and her team analyzed the data to assess how neighborhood types, yard conditions, house attributes, and window types influenced collision rates.

More collisions

The results suggest that wildlife-friendly properties may be a double-edged sword: Yards that are more attractive to birds are also the sites of more bird-window collisions.

Kummer and her colleagues found that three factors predicted collisions best: the presence of a bird feeder, whether a house was in an urban or a rural area, and the height of the vegetation in the yard.

A bird feeder increased the collision risk 1.7 times. Rural areas in the fall had a collision risk six times higher than urban areas in the winter. And trees more than two stories high increased the collision risk more than three times compared to houses with no trees.

“Although each typical residential dwelling causes only one or a few bird–window collisions per year, the enormous number of these buildings means we are killing far more birds in our collective backyards than are dying at large office buildings and skyscrapers,” said Scott Loss, lead author of the 2014 study.

The new study, he went on, provides an “excellent example of how the power of citizen scientists can be harnessed to address this major conservation issue.”

Kummer collected her data through a citizen-science project launched in 2013. Homeowners in Alberta walked the perimeters of their houses daily and reported evidence of bird–window collisions. Participants contributed more than 34,000 days’ worth of collision data. Of Alberta’s 421 bird species, 53 were represented in the data, mostly common urban species.

Most homeowners do not want to remove their feeders and wildlife-friendly vegetation, Kummer says. Instead, mitigation efforts should focus on evaluating the effectiveness of tape, film, and other products that can be applied to windows to prevent collisions.

“As homeowners don’t want to reduce the number of bird in their yards, I think the next step will be to determine the best window deterrents they can use at their homes.”

Read the paper

Justine A. Kummer, Erin M. Bayne, and Craig S. Machtans (2016) The Use of Citizen Science to Identify the Factors Affecting Bird-Window Collision Risk at Houses, The Condor: Ornithological Applications, Volume 118 (July 27, 2016), pp. 624–639.

American Bird Conservancy’s list of tested products that keep birds from striking windows.

Study: Birds strike windows of homes with, and without, feeders.

Study: Collisions with buildings kill 365-988 million birds annually.


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