PARENT SESSION
Oral Session #88: Wetland Ecology.
Presiding: K. Ewel
Thursday, August 8. 1:00 PM to 3:45 PM. Gila Meeting Room, TCC.

Snag production and use by primary cavity-nesting birds in beaver ponds in western Oregon.

FERN, J.^*,1, YEAKLEY, J.¹, ¹ Portland State University, Portland, Oregon

ABSTRACT- We hypothesized that beaver ponds create significantly more snags, and that those snags are excavated more extensively by primary cavity-nesting birds, than unponded forested stream areas. We randomly selected 8 beaver ponds and 8 reference sites (unponded forested riparian areas) in the western Oregon Cascades. At each pond and reference site, we mapped all snags and measured snag characteristics including diameter, height, decay class, percent bark remaining, type and number of excavations, excavating species and portion of snag excavated. We treated beaver ponds both as a pooled group (n=8) as well as old (n=5) or new (n=3) based on decay indicators. Reference sites (n=8) were treated as a pooled group. In new beaver ponds, snag density was higher (p<0.01), snags were in earlier decay stages (p<0.01) and usage by primary cavity-nesting birds was lower (p<0.01) than reference sites. In contrast, in old beaver ponds, snag density and usage by primary cavity-nesting birds were not significantly different from reference sites. Our results suggest that snags in new beaver ponds are smaller in average diameter, decay more quickly, and hence have lower cumulative usage by primary cavity-nesting birds than in reference sites. In riparian forests without beaver influence, snags form and decay more slowly, and are used more extensively by cavity-nesting birds.

KEY WORDS: avian ecology, forested wetlands, succession, woodpeckers