Graduate Thesis Or Dissertation
 

Abundance, habitat association, and foraging ecology of American dippers and other riparian-associated wildlife in the Oregon Coast Range

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  • To quantify the distribution and abundance of the riparian-associated vertebrate community, I surveyed streams in four basins in the Oregon Coast Range, 1992-1994. I observed mostly birds with fewer observations of mammals. Belted Kingfishers (Ceryle alcyon), American Dippers (Cinclus mexicanus), Great Blue Herons (Ardea herodias), and Mallards (Anus plalyrhynchos) comprised >85% of these observations, but no one species was abundant. Abundance of each species was affected by stream order, basin, and season, but to varying degrees. Dippers and kingfishers selected channel unit habitats disproportionately to their availability. Key habitat components that were predictive of use were species specific. Riparian forests and streamside trees were important predictors of use by the three most abundant species; dippers, kingfishers, and herons. Second, I studied nest-site selection of dippers. Dippers selected nest sites based primarily on micro-habitat characteristics. Reproductive success was high and not associated with any habitat or parental foraging behavior. Suitable nest sites provided a physical space to place the nest, were above the upper flood line and inaccessible to ground predators, and were very near or extended over the stream's edge. Within the context of mountain streams, dippers exhibited flexibility in their nest-site selection. Dippers used experimentally-created nest sites, doubling the population on a 10-km reach. Dipper populations appeared to be limited by the availability of suitable nest sites. Third, I studied foraging ecology of dippers by observing prey delivered to nestlings. Dippers fed nestlings a variety of invertebrate and vertebrate prey. Prey was mostly aquatic and composed primarily of mayflies, stoneflies, caddisflies, fish, and adult insects. Younger chicks were fed smaller prey and more mayflies than older chicks. Older chicks were fed larger prey and more caddisflies and fish than younger chicks. Mayflies, stoneflies, and fish were fed more often to nestlings during the first than the second brood-rearing seasons. The caloric content of prey delivered by males and females was similar. However, males delivered more, smaller prey items than females, and this was most pronounced when the females were brooding young chicks.
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