"Impact of invasive bird species monitored by Lab of Ornithology network"

According to this press release from May 2004, a citizen-science project called The Birdhouse Network (TBN) has initiated a Nest-Box Competitor Study for the purpose of "examining the effect of nest-box competition from invasive species on native cavity-nesting birds." Some excerpts:

According to 2003 data collected by TBN, house sparrows account for 43 percent of all competitor species (species that take over nest boxes intended for native birds). And although most nest-box (or bird-house) enthusiasts discourage nesting by house sparrows, the birds still comprise 10 percent of all reported nesting attempts when at least one egg is laid.

In head to head competition, house sparrows readily out-compete native species for nesting sites by evicting other nesting birds, destroying their eggs, killing nestlings and sometimes even killing the incubating female.