Submitted to: Northwest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2005
Publication Date: N/A
Citation: Interpretive Summary: Winter songbird abundance and diversity were related to percent tree cover along drainages in the south Willamette River basin. This is important because little baseline information exists regarding the impact of western Oregon agricultural land use on songbird populations. We conducted surveys that demonstrated that seventeen-times more birds were found along forested than non-forested drainages, but only 15% of the total land cover needed to be in trees to maximize songbird richness. Using our bird behavior findings and knowing that 70% of the watershed land area is less than optimal, farmers can now know where to target USDA conservation projects to enhance winter songbird populations.
Technical Abstract: We examined the association between winter bird community composition in nine one-square kilometer agricultural landscapes that included three types of riparian area management: farmed, shrub re-establishment, and forested common to grass seed agriculture that dominates the south Willamette River basin landscape. There were 17 times more birds observed per square km in forested riparian areas than in riparian areas with grass fields directly bordering the stream. There were over twice as many species observed per square km in areas with trees bordering the stream as with grass fields. For species with > 30 observations, habitat associations at both the scale of the sampling point and the landscape were consistent with life history information for the species. Not all species were associated with trees or shrubs, and not all that were associated with trees or shrubs need also to be near water. A significant curvilinear relationship was detected between tree cover in the landscape and winter bird species richness. Based on this relationship we hypothesize that providing 10-15% of a square km in tree cover would maximize winter bird richness within the range of conditions that we sampled.