Joan C. Hagar

Thresholds in forest bird occurrence as a function of the amount of early-seral broadleaf forest at landscape scales

Recent declines in broadleaf-dominated, early-seral forest globally as a function of intensive forest management and/or fire suppression have raised concern about the viability of populations dependent on such forest types. However, quantitative information about the strength and direction of species associations with broadleaf cover at landscape scales are rare. Uncovering such habitat relationships is essential for understanding the demography of species and in developing sound conservation strategies. It is particularly important to detect points in habitat reduction where rates of population decline may accelerate or the likelihood of species occurrence drops rapidly (i.e., thresholds). Here, we use a large avian point-count data set (N = 4375) from southwestern and northwestern Oregon along with segmented logistic regression to test for thresholds in forest bird occurrence as a function of broadleaf forest and early-seral broadleaf forest at local (150-m radius) and landscape (500-2000-m radius) scales. All 12 bird species examined showed positive responses to either broadleaf forest in general, and/or early-seral broadleaf forest. However, regional variation in species response to these conditions was high. We found considerable evidence for landscape thresholds in bird species occurrence as a function of broadleaf cover; threshold models received substantially greater support than linear models for eight of 12 species. Landscape thresholds in broadleaf forest ranged broadly from 1.35% to 24.55% mean canopy cover. Early-seral broadleaf thresholds tended to be much lower (0.22-1.87%). We found a strong negative relationship between the strength of species association with early-seral broadleaf forest and 42-year bird population trends; species most associated with this forest type have declined at the greatest rates. Taken together, these results provide the first support for the hypothesis that reductions in broadleaf-dominated early-seral forest due to succession and intensive forest management have led to population declines of constituent species in the Pacific northwestern United States. Forest management treatments that maintain or restore even small amounts of broadleaf vegetation could mitigate further declines.

Influence of riparian buffer width on bird assemblages in Western Oregon

The goals of current management practices in riparian areas in the Pacific Northwest includ protecting and maintaining habitat for terrestrial wildlife. However, little is known about the use of riparian buffers by terrestrial wildlife. particularly how buffer width may affect abundance and specics composition of wildlife communities. In this study. I compared bird assemblages in logged and unlogged riparian areas along headwater streams and assessed the relations between bird abundance and riparian buffer width. The abundances of 4 species of forest-associated birds that were more abundant in unlogged than in logged beadwater riparian stands (Pacific-slope flycatcher [Empidonax difficilis], brown creeper [Certhia americanu], chestnut-backed chickadee [Poecile rufesccus], winter wren [Troglodytes troglodytes]) increased with increasing width of riparian bnffers, However, 4 other species that also were more abundant in unlogged than logged riparian stands (Hammonds flyecatcher [Empidonax hammondii], golden-crowned kinglet [Regulus satrapa], varied thrush [Ixoreus nacvius], hermit warbler [Dendroica occidentalis]) were rarely observed in even the widest buffers sampled (40-70 m on 1 side of the stream), Although riparian buffers along headwater streains are not expected to support all bird species found in unlogged riparian areas, they are likely to provide the most benefit for forest-associated bird species if they are >40 m wide, and density of large trees within buffers is not reduced by harvesting.

Use of Nonalpine Anthropogenic Habitats by American Pikas (Ochotona princeps) in Western Oregon

ABSTRACT. The American pika (Ochotona princeps Richardson) has long been characterized in field guides and popular literature as an obligate inhabitant of alpine talus and as having relatively low dispersal capability. However, recent work reveals pikas to have broader habitat associations than previously reported. Over a large portion of the western slope of the Cascade Range in Oregon, pikas inhabit relatively low-elevation sites far from alpine areas and frequently occur in rocky man-made habitats such as roadcuts or rock quarries. We present observations of pikas in these previously overlooked habitats and discuss implications for (1) the proposed listing of the American pika as an endangered or threatened species; (2) furthering our understanding of pika population dynamics, habitat associations, and dispersal capabilites; and (3) management of federal, state, and private forest lands.

ARTHROPOD PREY OF WILSON'S WARBLERS IN THE UNDERSTORY OF DOUGLAS-FIR FORESTS

Abstract Availability of food resources is an important factor in avian habitat selection. Food resources for terrestrial birds often are closely related to vegetation structure and composition. Identification of plant species important in supporting food resources may facilitate vegetation management to achieve objectives for providing bird habitat. We used fecal analysis to describe the diet of adult Wilsons Warblers (Wilsonia pusilla) that foraged in the understory of Douglas-fir (Pseudotsuga menziesii) forests in western Oregon during the breeding season. We sampled arthropods at the same sites where diet data were collected, and compared abundance and biomass of prey among seven common shrub species. Wilsons Warblers ate more caterpillars (Lepidoptera larvae), flies (Diptera), beetles (Coleoptera), and Homoptera than expected based on availability. Deciduous shrubs supported higher abundances of arthropod taxa and size classes used as prey by Wilsons Warblers than did evergreen shrubs. The development and maintenance of deciduous understory vegetation in conifer forests of the Pacific Northwest may be fundamental for conservation of food webs that support breeding Wilsons Warblers and other shrub-associated, insectivorous songbirds.

Created snag characteristics and cavity-nesting bird associations in the CFIRP stands, McDonald-Dunn Research Forest, Corvallis, OR, USA, 2016

Snags provide critical habitat for nearly one-third of wildlife species in forests of the Pacific Northwest, so historic declines in snags are thought to have had a strong impact on biodiversity. Resource managers often create snags to mitigate the scarcity of snags within managed forests, but information regarding the function and structure of created snags across long time periods (>20 years) is absent from the literature. Using snags that were created by topping mature Douglas-fir trees (Pseudotsuga menziesii) as part of the OSU College of Forestry Integrated Research Project, we measured characteristics of 731 snags and quantified foraging and breeding use of snags by birds 25-27 years after their creation. We also examined whether different harvest treatments (i.e., group selection, two-story, clearcut) and snag configurations (i.e., scattered and clustered) influenced snag characteristics or avian use for foraging and nesting. In addition, we conducted point count and call play-back surveys to calculate naive occupancy estimates for cavity-nesting bird species.