Portland State University. Department of Biology
Richard B. Forbes
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Biology
Environmental Science and Management
2, vi, 178 leaves: ill., maps 28 cm.
Ecology, Ravens, Malheur National Wildlife Refuge (Or.)
Common Ravens (Corvus corax L.) have been implicated as significant predators on the eggs of waterfowl and shorebirds on Malheur National Wildlife Refuge. Malheur Refuge, located in southeastern Oregon on the northern edge of the Great Basin, is one of the largest waterfowl refuges in the United States and is an important breeding area for waterfowl. In order to provide fundamental information on which a sound raven management plan could be based, research was conducted from 1975-1977 on aspects of population density, brood phenology, nesting success, seasonal use of the study area, roosting behavior, and food habits of ravens on and near the refuge. Nesting density was determined to be one pair per approximately 25 km2 . Most nests occurred in rimrocks, but trees and abandoned human structures were also used. Investigation of 87 nests revealed that the incubation period was 21 + 1 days. Incubation began with the laying of the first egg; hatching was asynchronous. Nesting period was 41 + 3 days. An original method of age-classing ravens is described. A total of 266 ravens was marked with patagial tags. Observation of marked individuals as far as 480 km from the study area suggests considerable mobility in the population. Population numbers vary seasonally, peaking in the winter. The Harney Basin is the location of an exceptionally large winter roost for ravens. Analysis of food remains, collected from 34 nests, indicates that ravens have varied diets and that there are significant differences in the diets of ravens nesting in different habitats. A correlation exists between the proportion of the diet that is avian material and the proximity of the raven nest to waterfowl production areas. Based on these findings, suggestions are offered for a management plan for Common Ravens on Malheur National Wildlife Refuge.
Stiehl, Richard B., "Aspects of the ecology of the common raven in Harney Basin, Oregon" (1978). Dissertations and Theses. Paper 762.