This article is from the Birds FAQ, by Lanny Chambers with numerous contributions by others.
European Starlings (Sturnus vulgaris) and House Sparrows (Passer
domesticus) are European species that have been introduced in several
parts of the globe. In particular, Starlings were introduced to North
America by one man, Eugene Schieffelin, who wished to increase the
popularity there of William Shakespeare; he set out to introduce all
the birds mentioned in the Bard's writings. Starlings were his greatest
In areas where they are native, these species receive both affection
and scorn, as does any aggressive or conspicuous species in its home
range. In areas where Starlings and House Sparrows have been introduced,
however, they compete for food and nesting sites with native species;
thus they have a detrimental effect on biological diversity. The decline
of cavity-nesting birds (such as bluebirds, Sialia spp.) in North America
has been attributed in part to them.
Because they are not native species, these two, along with city
pigeons ("Rock Pigeons," Columba livia) and Muscovy "ducks" (Cairina
moschata), are not protected in North America.