You see them everywhere… singing outside your bedroom window, eating squashed bugs off your car windshield, cleaning up spilled crumbs at sidewalk cafes. They mob bird feeders full of millet and take up space in nest boxes intended for other species. I’ve even found them in a tiny town in the middle of the Utah desert, miles from anything wet or green. One would think that House Sparrows are one of the most successful species ever to populate planet Earth.
Not closely related to North American sparrows, House Sparrows are relative newcomers to the Western Hemisphere. They were deliberately introduced during the latter half of the 19th century in repeated attempts to establish a breeding population in the U.S.
While the story is a bit foggy, apparently the birds were imported to eat insects that were damaging crops. If so, it was an egregious error. House Sparrows are primarily seed eaters, and according to one study, 78% of those seeds come from agricultural crops intended for livestock or human consumption.
As early as 1887, people were becoming aware of the mistake that had been made. States began to pass laws encouraging the extermination of the immigrants, but it was far too late. There are now approximately 150 million House Sparrows living in the Western Hemisphere—from Canada to Central America, and throughout the temperate parts of South America.
As the numbers of House Sparrows soared, they began to have a detrimental impact on several species, including Tree Swallows and Purple Martins. However, the most serious repercussions involved bluebirds.
For a variety of reasons, bluebird populations took a nose-dive during the early 1900s. Winters during the 1890s were exceptionally severe, and many birds died. It takes time for populations to recover, and the repeated cold weather was very damaging, at least to Eastern Bluebird numbers (no one was counting Western and Mountain Bluebirds at that time).
Both bluebirds and House Sparrows nest in holes excavated by woodpeckers. During the last several hundred years, much land that used to be forested has been cleared for farming. So much land has been cleared that there are few trees available for perching and nesting. Also, because dead trees are now routinely cut down, fewer rotting trees with holes in them are available for the birds to use. If the birds can’t find a suitable cavity for their nest, they are unable to breed for that season.
Of the two species, House Sparrows are much more aggressive than the even-tempered bluebirds. They will evict bluebirds from their homes, often killing both the nestlings and the parents in the process. People who provide nest boxes for birds such as bluebirds, swallows, chickadees and nuthatches are responsible to ensure that no House Sparrows harass their tenants.
In a curious case of come-uppance, the House Sparrow is actually the victim of another introduced species, the House Finch. While House Finches are native to the west, they were limited in their range until a number of birds were released on Long Island, NY, in the 1940s. The highly adaptable species quickly colonized its new territory. House Finches are now found from northern Florida into Canada. At least in the eastern U.S., as the newcomer finches usurp food and nest sites, House Sparrow numbers have decreased. (See www.birds.cornell.edu for more information.)
While most birdwatchers in the U.S. consider House Sparrows anathema, the situation is strikingly different in Europe. In their native habitat, these birds are in serious trouble. Recent surveys show a 60% decrease in sparrow populations in Great Britain and western Europe. (Other songbirds are also experiencing significant reductions in population numbers.) The causes are unknown, and probably complex, although habitat destruction must play a significant role. It is certainly ironic that a bird considered a pest species in our country is now on the threatened species list at home.