Illinois State Museum
Change Is Good for Whom?
Since the arrival of the first people in Illinois, human actions have affected the environment. Natural forces have also continued to change climate, land, and life. Determining the impacts of environmental change is difficult. Every change in an ecosystem starts a chain reaction that benefits some species and sends others to extinction.
Making Connections: People, Cowbirds, and Other Birds
Which species benefited from environmental changes?
Brown-headed Cowbirds (Molothrus ater) are wide-ranging prairie birds that feasted
on insects stirred up by grazing bison.
These small birds are nest parasites. They lay their eggs in the nests of other birds, such as warblers and vireos. They leave the care of the eggs to the foster parents. The cowbird's eggs hatch first, and the young cowbirds consume all the food brought by their foster parents. Cowbirds grow quickly and push out the chicks of the bird that built the nest.
Forest Fragmentation
Human activities, however, have changed this native bird's way of life (and
that of many other North American birds). Highways, agriculture, and urban sprawl
have opened up new habitats for the cowbird. As human-made environments expand
into forests, they become corridors that allow cowbirds to reach the nests of
birds once protected by deep-forest.
Good or Bad?
Forest fragmentation has been good for cowbirds. These birds have spread from
coast to coast in North America. The changes have been bad for other bird species.
Cowbirds lay their eggs in the nests of 62 species of Illinois birds. Some of these
birds are now scarce because of this aggressive nest parasite.