"This mirrors nationwide results previously reported by Audubon," says Pidgeon.
Now, Pidgeon has expanded the study to begin to examine how the pressures of housing growth and land cover change have altered bird populations during the past 30 years across the 48 contiguous United States. "We are seeing geographic clusters within the U.S. where some species populations are increasing, which we suspect is due to increases in both generalist and exotic species," says Pidgeon.
While human population has grown significantly across the continental United States since the 1970s, Lepczyk says the number of houses sprouting up in previously undeveloped areas is likely having a greater impact than the raw number of humans inhabiting the landscape.
"Houses, we think, may represent a better indicator of impact (on native bird species) than human population," Lepczyk explains.
The study results portray an increase in exotic bird and generalist species, such as European starlings, pigeons, crows and jays, as a consequence of increased housing density on the rural landscape.
What clearly puts some native forest species at risk is the outright loss of wooded habitats as roads and lawns replace native vegetation, says Pidgeon. Not only does such development shrink available breeding habitat, but it also opens corridors for bird predators such as raccoons and skunks. Lawns also provide foraging areas for brown-headed cowbirds, parasitic birds that lay eggs in other birds' nests.
"Roads provide access and increased edges that nest predators including jays and crows use," Pidgeon says, "and we know from the work of others that an increase in predation accompanies an increase in housing density" as the domesticated animals that accompany humans, cats and dogs in particular, exact a heavy toll on native forest bird species.