Date of Award:
Master of Science (MS)
Keith L. Dixon
Censuses of two 20-acre plots in upper Logan Canyon, Utah, were made by the spot-mapping method during 1970 and 1971 to determine the differences in composition and density of breeding-bird populations in aspen stands of significantly different density and stature. The less dense stand of greater average d.b.h., average height and per cent ground cover had 20 breeding species totalling 615 pairs per 100 acres (expressed as equivalent territories). The more dense stand of smaller trees and brushy undergrowth had 14 breeding species with 267.5 equivalent territories per 100 acres. Nine species were found on both areas. Observations of foraging height were made concurrently with recordings of time spent at various methods of feeding- ground, vi foliage, bark, hover, and hawking- for the birds of the more open stand. Comparison showed that more ground- and low bush-nesters were present on the dense, brushy stand whereas more cavity-nesters were found in the larger trees. Cavity excavation was limited to trees of greater d.b.h. and cavity-dependent birds were thus limited by nest-hole availability. The horizontal, heavy branch stubs preferred by pewees and tree swallows and the high perches and open areas of the olive-sided flycatcher were also limited to the less dense stand. Cassin's finches and pine siskins were not found in the dense stand which had fewer invading conifers and was farther from conifer stands. Attributes of the terrain, foraging sites, nest sites, and location of perches were analyzed as possible proximate factors of habitat selection within aspen.
Young, Janet L., "Breeding Bird Populations and Habitat Utilization in Aspen Stands of Upper Logan Canyon" (1973). All Graduate Theses and Dissertations. 2203.