The House Sparrow and European Starling:

Avian Immigrants and their impact in the United States

Steven M Howell

In combating the loss of biodiversity throughout our country, conservation biologists tend to focus on minimizing habitat loss. The introduction of exotic species, however, can be just as damaging to the biodiversity of ecosystems (Culotta 1991). Introduced species brought from other countries (or different regions of the United States) can proliferate to the extent that they threaten the survival and success of native species; large populations of introduced species can have tremendous effects in their new environments, often ending in the decline and possibly the extinction of the native species. Once introduced, exotic species can have numerous ecological impacts. Such impacts include domination of the ecosystems by the introduced species, as seen with the introduction of zebra mussels; degradation of ecosystems, such as with Chinese tallow's effect in altering the physical and chemical properties of their environment; and predation on native species by introduced species, as seen with the introduction of the brown tree snake (Culotta 1991). Introduced species can displace native species through competition for certain biological niches within ecosystems. Introduced avian species, such as the European starling and house sparrow, serve as good examples of this displacement of native species through competition.

Since the 1800's, thousands of foreign plant and animal species have been introduced and established themselves in the United States. Introduced bird species provide an excellent example of the problems arise with the establishment of exotic species. The growing dominance of introduced bird species is seen in the increase in population sizes of such birds as rock doves, house finches, house sparrows, and European starlings (Gill 1995). Many exotic bird species were first introduced in the mid-to-late nineteenth century by European immigrants intending to improve their new surroundings with familiar European birds. Acclimation societies were established across the country which acclimated and released several thousands of birds, including the European starling (Sturnus vulgaris) and house sparrow (Passer domesticus) (Arcieri 1992).

In the 1890's, one such acclimatization society, headed by Eugene Schieffelin, decided to release into the United States all of the birds mentioned in the works of Shakespeare (Ingold 1989). Starting with only a few pairs of European starlings released in New York's Central Park, the starling became Mr. Schieffelin's biggest success. Living in large flocks, starlings have become one of the most abundant and widespread birds in America (Stokes and Stokes 1989); starling populations are found from the east to the coast and from Alaska to southern Mexico (Kerpez and Smith 1990). Starlings have been found to have serious detrimental effects to native bird populations, such as with red-bellied and gila woodpeckers, bluebirds, and swallows. Starlings compete with these native species for nest cavities in trees. Although starlings use cavities in trees for nests, they do not excavate their own. Thus, starlings have a negative impact on native species through displacing native species by taking nest habitats and often destroying eggs and fledglings in the process.

The effects of European starlings on native species have been studied throughout the United States (Ingold 1989, Kerpez and Smith 1990). Kerpez and Smith (1990) examined the effects of breeding starling populations on breeding gila woodpeckers and northern flickers in Arizona. They found that breeding starlings have a negative effect on gila woodpeckers because of competition for nest cavities in saguaros trees. The researchers also noted the numbers of gila woodpeckers have decreased dramatically in habitats shared with starlings. Likewise, Ingold (1989) studied the decline in breeding success of red-bellied woodpeckers due to starling nest cavity competition in Mississippi. He found that red-bellied woodpecker reproduction was indeed reduced as a result of aggressive starlings competing for nests. Data from the Breeding Bird Survey (Sauer et al. 1996) show that gila and red-bellied woodpecker population numbers have been maintained at relatively low numbers in Arizona and Tennessee compared to the increasingly abundant European starling since 1980. Although these data do not definitely prove that starlings are displacing native species, the population numbers from the Breeding Bird Survey support the accepted notion that increasing starling numbers have negative effects on native species.

Like the European starling, house sparrows were introduced from Europe around 1850 and have since experienced an enormous increase in population size (Arcieri 1992). House sparrows are not related to native North American sparrows. Instead, they are most closely related to weaver birds (Family Ploceidae). Sometimes called the English sparrow, house sparrows are characterized as aggressive birds which often take over the nests of native swallows, bluebirds, and house wrens. The worst problem with the introduction of the house sparrow seems to be also related with the displacement and decline of native bird populations (Arcieri 1992). Although the data obtained from the Breeding Bird Survey (Sauer et al. 1996) concerning the declining population sizes of the barn swallow and eastern bluebird was inconclusive, other studies have shown that house sparrows do compete for the same nest cavities with swallows and bluebirds (Culotta 1991, Arcieri 1992, Edge 1996). It would seem that the ubiquitous house sparrow would decrease the breeding success of these native birds through nest cavity competition. Other problems associated with increasing numbers of house sparrows include aesthetic and mechanical damage to houses and buildings and damage to crops through foraging on wheat and corn grain.

If introduced birds are a major threat to biodiversity in the United States, what measures are being taken to retard the proliferation of these species? The scientific community remains uncertain about the best way to deal with the situation (Culotta 1991, Arcieri 1992). Proposed solutions range from efforts to totally stop the introduction of foreign species to the introduction of natural predators from the introduced species habitat. To help fight the rising numbers of introduced bird species, law permits individuals to kill, capture, or collect certain non-native birds without permits. The Migratory Bird Act protects all common wild birds in the United States except the house sparrow, European starling, and feral pigeon (Ingold 1989). There are ways individuals can discourage the success of house sparrows and starlings in their own backyards. These ways include blocking entrances to bird houses, cavities, or nest boxes until native migratory birds arrive; make nest boxes with 1 1/8 inch diameter openings to favor song birds; and place protected nesting boxes and bird houses within 4 feet of the ground to discourage nesting house sparrows (Edge 1996).

A major contributor to the depletion and extinction of native bird species, possibly second only to habitat loss, is the introduction of non-native birds, such as the European starling and the House Sparrow. The negative effect of starlings and house sparrows is due to their growing population sizes and its subsequent effect on the competition for nest cavities between these non-native and native birds. Although no clear solution has been presently recognized, efforts are underway to limit the number of exotic bird species introduced into the United States and to retard the growth of established exotic bird species.

Literature cited

Arcieri, D.T. 1992. Undesirable Alien - The House Sparrow. Conservationist 46: 24 - 25.

Culotta, Elizabeth. 1991. Biological Immigrants Under Fire. Science 254 (5037): 1444 - 1447.

Edge, Dan. 1996. Problem Birds - house sparrows and starlings page (ed: Carol Savonen), Oregon State University, OR.

Gill, Frank. 1996. Ornithology. 2nd Edition. W.H. Freeman and Company, New York, NY, USA.

Ingold, Danny J. 1989. Look, Mom, No Cavities. The Living Bird Quarterly 8(3): 24 - 28.

Kerpez, Theodore and Smith, Norman. 1990. Competition between European starlings and native woodpeckers for nest cavities in saguaros. The Auk 107 (2): 367 - 375.

Sauer, J.R., B.G. Peterjohn, S. Schwartz, and J.E. Hines. 1996 The North American Breeding Bird Survey Annual Indices - Graphs of Bird Population Change Over Time. Version 95.1. Patuxent Wildlife Research Center, Laurel, MD.

Stokes, Donald and Stokes, Lillian. 1989. Starlings. Living Bird Quarterly 8 (2): 30 - 31.