There are certainly lots of accounts of House Sparrows taking over nest boxes that native birds are using. One would assume that this would impact native bird populations, but we don?t know for sure. Maybe the displaced birds were able to nest elsewhere, assuming that they weren?t killed (see below). Probably not, given the shortage of cavities in urban areas, but for sake of argument let?s say that displaced natives are able to nest elsewhere during that breeding season.

A more direct impact on native bird populations would be through House Sparrows puncturing eggs, killing nestlings, and even killing adult birds in the nest box. It is well documented that they do this. For eyewitness accounts and photos (warning, they are gruesome) see: http://www.sialis.org/hospattacks.htm

Mike Donahue
Seattle

47.33.11 N 122.18.13 W
320 ft