Are migratory birds more likely to strike windows?

The house that I rent in Santa Cruz has several large, plate glass windows. From time to time I find a stunned bird sitting below these windows, and more often than not the bird is migratory. Although I don’t keep a record of window strikes, my recollection is that three birds have struck the windows so far in 2013: one Red-breasted Nuthatch and two Pine Siskins (including one this morning). Both of these species breed in northern coniferous forests and winter on the central coast of California (some Red-breasted Nuthatches also breed locally). This observation makes me wonder whether migrants are more likely than residential birds to hit windows.

I would not be surprised to learn that there is natural selection for birds that are better at detecting windows. It’s been estimated that one in two window strikes will kill a bird, and this kind of mortality should exert a strong selection pressure for birds that are frequently exposed to window-striking opportunities. Since the residential birds in my yard, like Lesser Goldfinches and Pygmy Nuthatches, are here all year, presumably they deal with reflective glass more frequently than their cousins that spend much of the year in the vast windowless wilderness of the boreal forest. (A friend wryly suggests that this hypothesis could be tested by installing plate glass obstacles in Canadian forests).

For an interesting discussion of the impacts of reflective skyscrapers on birds during nocturnal migration, see this piece about Toronto by New York Times writer Ian Austen.


About Leighton Reid

Restoration Ecologist
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