We've all heard about the problems that result when people introduce wildlife into new places. Animals released into areas where they didn't develop often can't survive. Other times, they win out over native species in the complex competitions for food and habitat. When this happens their populations can swell, and they can become established over large areas very quickly. In fact, two unwilling immigrants can probably be found in your backyard—no matter where you live.
Biblical Sparrows
House or English sparrows (Passer domesticus) were first released in 1850 and 1852 in Brooklyn, New York, but more were introduced in other northeastern sites before 1870. These gregarious little birds spread across the continent with astonishing speed. Today they're year-round residents throughout Canada, the United States, and Mexico, primarily in agricultural, suburban, and urban areas—in short, wherever people have cleared the land. They even live inside buildings like airport terminals, malls, and large warehouse stores. In fact, house sparrows have learned to open the automatic doors to such structures by flying in front of electric eye door sensors!
These birds are a kind of weaver finch, who build nests with openings in the sides. Native to Eurasia and North Africa—and the sparrow species mentioned in the Bible—they're now believed the most ubiquitous birds in the world.
House sparrows are about six inches long from their strong bills to their short tails and have short wings and stout little bodies. Females and youngsters are undistinguished, with gray-brown throats, breasts, and bellies and brown backs with black streaks. Males sport chestnut-red temples and napes and distinctive black chins, throats, and bibs around white cheeks that always remind me of Vandyke beards.
They forage on the ground in small flocks for grass and weed seeds but also eagerly take food scraps and visit birdfeeders. You'll see them inspecting sidewalk trash in almost any city in the country—or pecking insects off automobile radiator grills in summertime parking lots.
House sparrows will nest on tree branches but prefer tree cavities, crevices in buildings, and nest boxes. Their nests—reused from year to year—look like untidy dome-shaped masses of twigs, leaves, paper, feathers, and string, and a mated pair can have several broods in a season.
Males remain in their territories all year long, aggressively defending them during breeding season. This can prevent late-arriving migrants from nesting—earning house sparrows a reputation as threats to native songbird populations, but sparrow numbers have been in decline for the past several years.
Shakespeare's Starlings
In 1890 Eugene Schiffelin released 60 European starlings (Sturnus vulgaris) in New York City's Central Park. He wanted to introduce every bird mentioned in William Shakespeare's works into this hemisphere. (Starlings are mentioned in Henry IV.) His comrades released perhaps 40 more within the next year, and the birds built one of the first nests here—with unwitting irony—under the American Museum of Natural History's eaves.
Spreading rapidly, starlings reached California within 50 years and thrive today from southern Alaska across Canada and south to Florida and northern Mexico. Now more than 200 million live on the continent.
About eight inches long, they have short, square tails and pointed, triangular wings. Both sexes are black with white triangular feather tips spotting their bodies. The tips are lost to wear by breeding season, leaving iridescent black feathers with a green and purple sheen. Their long, straight bills are yellow during breeding season but darken at other times. Starlings are related to mynas and mockingbirds and—like them—can mimic other birds' calls. You'll see males drop and loosely spread their wings when singing.
They're native to northern Eurasia and live here—like house sparrows—wherever people do. They avidly eat insects and other invertebrates and berries. You'll recognize them waddling along in the grass, probing the ground, using special jaw muscles to pry their bills open in the soil to catch insects other birds can't reach. This feeding behavior—gaping—helps them thrive during winter in places other insect eaters can't survive.
At night starlings form flocks and large communal roosts that sometimes number more than a million birds. They're at least partly migratory in the northern reaches of their range, with some birds moving south from September to early December and returning north from mid-February to late March while others stay put.
They're strong competitors for nesting sites in tree cavities and on buildings and can evict other cavity nesters like eastern bluebirds—and even excavators like woodpeckers. For this reason starlings have been blamed for reductions in other birds' numbers, but a recent study showed they have little effect on more than two dozen native species.
Live and Let Live
The spread of introduced animals poses a dilemma. We don't want to see native animals threatened, but we also don't want newcomers treated inhumanely in misguided attempts to control them. While house sparrows and starlings have probably stressed some bird populations, they're no less deserving of our compassion than other animals. And they shouldn't have to pay for the mistakes people made by releasing them here.
Fortunately, we can help native bird species without harming introduced ones. If you feed birds in your backyard during the winter, supply niger (or thistle) seed in feeders with special narrow slits for songbirds. If starlings or sparrows dominate the feeder, put others around your property or replenish the seed once they leave for the day. Using a variety of birdseeds might help, as well. And provide suet cakes or peanut butter for native cavity nesters like woodpeckers and nuthatches. Similarly, leave dead trees that won't pose a danger standing on your property to provide habitat for these birds. Brush piles and native plantings will provide shelter and food for all your feathered visitors, too.
Above all, try to appreciate starlings and house sparrows for who they are. Their ability to thrive in a new land proves them to be marvelous little birds—world travelers in your own backyard.
—Michael Blankenship 
