Human settlement and avian communities in lowland riparian areas.
MILLER, J.R.* 1, J.A.WIENS 2 and N.T.HOBBS 2,3
University of Wisconsin, Madison, WI 53706 1
Colorado State University, Fort Collins, CO 80523 2
Colorado Division of Wildlife, Fort Collins, CO 80526 3
In western North America, riparian habitats have been characterized as centers of avian diversity, important to both migrating and breeding birds. Human settlement also tends to concentrate along rivers, but our understanding of the effects of settlement on bird communities is still rudimentary. From 1995-1997, we censused birds in riparian woodlands during the breeding season at 16 locations on four drainages near the Front Range of Colorado, an area that has been experiencing rapid population growth over the last few decades. These study sites were chosen to represent a gradient of development on each drainage, as measured by the intensity of settlement in the surrounding landscape. We found that ground cover, and native trees and shrubs decreased with settlement intensity whereas tree height, number of bridges (a measure of habitat fragmentation), and human activity in the riparian zone increased with development. Both the number of bird species and the number of individual birds were negatively correlated with settlement intensity. Although there was little similarity between avian communities at rural study sites and bird assemblages associated with the surrounding grasslands, riparian avifaunas at highly developed sites were essentially comprised of birds that are typical of developed areas in this region. Ordination analyses showed that most neotropical migrant species were associated with lower levels of settlement intensity and increases in the amount of understory. Resident bird species, however, tended to be most abundant at developed sites or were evenly distributed across the entire gradient of development. Our results indicate that human settlement exerts a strong influence on both the habitat structure of these riparian woodlands and on the bird communities found there. Moreover, our data suggest that effective conservation of avian diversity depends on careful consideration of the landscape context in which these habitats occur as well as an appreciation for the effects of human activity occurring within the riparian zone.
Keywords: bird community, urbanization, human settlement, riparian, western U.S.
This abstract is being presented at: 3:45 PM in session:
Oral Session #14: Disturbance Effects on Bird Populations.