No sparrow or longspur species are listed as endangered or threatened in Illinois. While that news is good, it does not mean that their populations do not face challenges.
Two of the species depicted on this poster, the house sparrow and Eurasian tree sparrow, are exotic, invasive species. Until the mid- to late-1800s, these species did not exist as wild populations in North America. A small number of house sparrows from Europe were originally released in New York City in the mid-1800s and in other states soon afterward. The species can occupy almost any habitat except dense forest, they produce more than one brood per year and, with no natural predators, the population spread tremendously. House sparrows are extremely common birds in Illinois. A few Eurasian tree sparrows were released in St. Louis, Missouri, in 1870. They established a population but were displaced from the city by the arrival of the house sparrow. They adapted to other habitats and now can be found in Illinois, Missouri and Iowa. In Illinois, the Eurasian tree sparrow lives in the west central portion of the state. Both species have similar nesting requirements. They nest in cavities or partially enclosed spaces, including natural and human-made objects. They are aggressive and often take over nesting spaces used by native birds. When these species are in competition for nesting spaces with each other, the house sparrow generally wins. It may be one reason that the Eurasian tree sparrow's population in the United States has not spread widely. The huge number of house sparrows in the state reduces available food for native species, too.
Many native sparrows in Illinois are targets for nest parasitism by the brown-headed cowbird (Molothrus ater). Affected species include the eastern towhee, chipping sparrow, field sparrow, vesper sparrow and song sparrow. Brood parasites are birds that lay their eggs in the nests of other birds (host species). The parasite's eggs hatch and are raised by the host species. The brown-headed cowbird is the most common nest parasite in North America. Many of the host species that co-evolved with brood parasites have reduced the success of parasites through strategies such as building a new nest or pushing the parasite eggs out of the nest. However, if a host species has not co-evolved with a parasitic species, the host may not be able to cope with parasitism. The brown-headed cowbird, prior to European settlement, was found in the western part of our country in open grassland. It followed American bison (Bison bison) herds, eating insects from their dung and from the prairie disturbed by their hooves. Because it followed the herd it could not incubate its own eggs and raise its young, so cowbirds adapted by using the nests and parenting abilities of other birds. Because the host parent birds are attending to the parasite young, often few or none of the host's own young survive. Young cowbirds tend to hatch and develop more quickly than most songbirds’ young. Often they are bigger too, and they may push others out of the nest. With settlement and the subsequent deforestation of large areas of eastern North America, the range of the cowbird expanded greatly, negatively impacting a variety of native bird species.
Native sparrow populations have fluctuated over time based on available habitat. When grassland and open habitats expand, those species associated with them may be more successful while those species associated with more wooded habitats will decline. When wooded habitats increase, species associated with them increase, and species found in open lands may decline. A good balance of a variety of habitat types is required to maintain a healthy biodiversity. Changes in habitat availability are normally due to human actions.