Over 115 miles of rock revetments that serve to protect river banks have been constructed in the Willamette Basin. In this study the spring and summer bird use of Willamette Basin revetments is examined. Revetments that had not been recently cleared of most woody vegetation and blackberries were found to have significantly greater total and breeding bird use than cleared revetments. Possible factors affecting bird use, such as vegetation on revetments and vegetation adjacent to revetments are examined using linear regression analysis. The results of this study are compared with results of previous work in riparian forests along the Columbia River. It is concluded that revetments represent significant avian habitat, especially for "edge species," and that present maintenance practices involving removal of vegetation adversely affect bird use.

A study was undertaken to determine the abundance, distribution, perching heights, diets and territory sizes of Red-Tailed Hawks on Sauvie Island, Oregon. Sauvie Island supported a large wintering population of non-territorial Red-Tailed Hawks. The establishment of territories began around 10 January. Average perch height was found to be 14.2 m. Average perch height increased from fall to spring, corresponding-to the onset of the breeding season and to the onset of egg-laying and incubation. Voles (Microtus spp.) were the principal prey year-round, though waterfowl were more important in terms of biomass in the winter and early spring. Territory sizes on the Island ranged from .31 - 3.73 km squared The abundance of voles was assessed in different habitats within five Red-Tailed Hawk territories. Territory size was shown to be inversely correlated to the population density of voles. The implications of this finding for the type of territoriality exhibited by Red-Tailed Hawks is discussed, as are some proximate factors affecting habitat selection.

Thesis (M.S.)--Oregon State University, 1991. / Typescript (photocopy). Includes bibliographical references (leaves 71-81). Also available via the World Wide Web.

Over fifty percent of humans live in cities. The environmental cost of this is massive, as is the potential for utilizing privately held yards as an integral part of conservation in urban areas. The Backyard Habitat Certification Program (BHCP) in Portland, Oregon, was established to reduce invasive plants, support wildlife, and promote conservation. The program involves > 3000 yards certified at three tiers. While onsite inspections are required to verify compliance, there has never been an assessment of the value of these yards to wildlife. Chapter 1 examined the relationships between the urban landscape and bird distributions outside of yards. Chapter 2 evaluated the ability of the program to separate yards by assessing differences in vegetation structure and composition. Chapter 3 tested if avian abundance, richness and diversity in yards are a product of responses to yard or landscape vegetation structure. Avian data was collected at 146 yards and 73 random locations in 2013 and 2014. Public landscape data was used to collect yard data in the field. Avian abundance, richness, and diversity were affected negatively by urbanization (especially impervious surface) and population density, but positively by tree cover. The BHCP was effective at distinguishing platinum yards from others, but overlap was relatively high among gold, silver and uncertified yards. Avian abundance, richness and diversity within yards was less affected by yard vegetation than the structure of habitat in the surrounding landscape. Species responded individualistically to yard vegetation and the urban landscape, and response was a continuum of tolerance to urbanization. Ultimately, the ability of yards to support wildlife will depend on wide scale neighborhood participation.

The effect of contiguous forested habitat area on local avian diversity and species richness in the Tualatin Mountain area of northwestern Oregon was investigated. Observations of eight forested stands representing seven area values (1, 2, 7, 14, 18, 24 and 40 hectares) were made during the spring and summer of 1991 and 1992. The variables measured were chosen in an attempt to show possible relationships between vegetation factors, spatial patterns and bird communities. Kendall's rank correlation coefficients were used to analyze the data. Avian species richness and diversity were significantly correlated with forest stand (patch) size. The only significant correlation between avian species richness and diversity and vegetation measures was with percent shrub layer cover. It seems likely that avian diversity and richness are increased due to the presence of species that can utilize the interior and edges of forest stands along with species which depend upon true forested interior. When forested patch size drops below a critical area, the patch becomes all edge. Interior species are absent due to increased predation and the inability to compete with interior-edge species. Edge effect may be a contributing factor to variation in diversity of birds. The correlation of percent shrub layer cover with avian measures is accompanied by a correlation of percent shrub layer cover with distance from edge. This suggests further investigation is required to assess this relationship. Studies conducted in the northeastern and north central United States have shown a similar relationship between bird communities and forest patch size.

Part I of this study presents a procedure for standardization of pellet analysis methodologies which improves estimation of prey biomass and determines the number of pellets needed to estimate prey diversity indices. The procedure was developed to provide a simple, easily replicated methodology for the study of pellets which also retains maximal data recorded from pellet analysis. A sample size of ten Long-eared Owl pellets was found adequate to calculate diversity indices with no significant loss of accuracy when compared to total pellets recovered from beneath a roosting site. Analysis of the total sample of pellets from a specific roost provided information on intraspecies size selection by Long-eared Owls and also increased the probability of finding remains of rare prey in pellets from the areas studied. Part II of this study investigates the influences of seasonality and habitat differences on prey selection by Long-eared Owls in north-central Oregon. Differences in habitat where Long-eared Owls foraged were found to significantly influence prey species selection of Thomomys talpoides , Lagurus curtatus, Peromyscus maniculatus, Microtus montanus, and Perognathus parvus. Significant seasonal differences were also observed in the consumption of T. talpoides and M. montanus. Analysis of intraspecific size selection of northern pocket gophers by Long-eared Owls supports the observation that size of prey influences the foraging strategies of Long-eared Owls to a greater degree than does species composition.

This study is an analysis of the various factors affecting the population of raptorial birds on Sauvie Island, Oregon. A census of diurnal and nocturnal raptors was carried out along with an analysis of food habits. Once the major prey species were determined they were censused, and the effects of the land management practices on their numbers was investigated. In addition, 100 randomly selected nest boxes were sampled so as to determine the extent to which raptors were making use of them. Red-tailed hawk and Great Horned Owl nests were located It was found that four diurnal raptors and three nocturnal raptors were present in sizeable numbers on Sauvie during the winter and spring of 1972. In addition here were less common sightings of four diurnal and one nocturnal raptor. The most common food item of raptors in general was the vole, Microtus townsendi, which was later found to be present in extremely high numbers. The common practice of planting fields of grains and the intentional flooding of them (for waterfowl use) was found to be a major factor in the numbers and vulnerability of Microtus townsendi. Ducks were a common food item for all raptorial species during and immediately after duck hunting season, but not at any other time of year which seemed to indicate that the raptors were feeding on carrion or wounded ducks. It was found that Barn Owls (Tyto alba), Screech Owls (Otis asio) and Kestrel (Falco sparvarius) made use of the nest boxes on Sauvie Island. The overlapping of food habits of Sauvie Island raptors was discussed and an attempt was made to reconcile the apparent contradiction to Gause’s Rule.

The lack of suitable nest sites may be a limiting factor for Western Bluebird populations inhabiting the upper Willamette Valley. Nest box trails have been established on the hills surrounding the Portland metropolitan area. Since their placement, approximately 25% of the boxes available have been used by Western Bluebirds as nest cavities. This study was undertaken to identify factors which might determine the selection of a nest box by Western Bluebirds and the subsequent nest success or failure. The breeding biology of Western Bluebirds using the nest box trail located on Parrett Mountain, Oregon in 1979 was investigated. Breeding season, mean clutch size, average incubation and nestling periods, and level of nest success were determined. Nest box dimensions, placement, and surrounding habitat features were quantified. Potentially important nest site characteristics were examined and tested for association with Western Bluebird nest box use and reproductive success. Western Bluebird nest box selection was random with regard to all of the characteristics studied except Solar Index and Nest Box Density. No correlation was seen between nest box characteristics and bluebird nest success.

The effects of urbanization and continual human disturbance on the plant and avian communities of Forest Park and forested lands surrounding Portland, Oregon, were studied. I examined characteristics of plant and avian communities at 25 sites, 24 which were in Forest Park and surrounding areas and one which was in the Ancient Forest Preserve (old-growth stand) northwest of Forest Park. Data were analyzed using multiple regression, ANOV A, and Bonferonni/Dunn. Seven variables were selected representing different urbanization gradients. An additional covariable coded for the old-growth stand, allowing it to be used as a control. Many tree variables, especially those related to shade-tolerant species, were positively correlated with both the distance from downtown Portland and the number of houses in the surrounding area, and negatively correlated with the distance from the nearest forest edge; however, many shrub and herbaceous variables were negatively correlated with the distance from downtown Portland. Species diversity for herbaceous and shrub species was greater at more urban sites, but diversity of trees was lower at more urban sites. There were significantly more non-native species of plants in the city section. I found significantly fewer saplings and small trees, especially shade-tolerant species, in the section of Forest Park closest to downtown Portland, although tree mortality was positively correlated with distance from Portland. Summer bird data revealed significant increases in the abundances of urban and edge species at more urban sites, with concomitant reductions in forest species. There were significantly more ground gleaning birds and short distance migratory species. I also found a significantly greater abundance of birds in the old-growth stand during the winter. This increase was positively correlated with the depth of snow in the nearby Cascade Mountains. My results indicate that Forest Park is apparently progressing in a normal successional pattern with the exception of the city section. The reduction in shade tolerant saplings and small trees in the city section suggest that rate of succession has been slower at more urban sites. Avian data suggest that urbanization affects bird species abundance and guild composition in the more urban areas.