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An analysis of guild structure of avian communities, Columbia River, Oregon

ScholarsArchive at Oregon State University

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Title An analysis of guild structure of avian communities, Columbia River, Oregon
Names Noyes, Cecilia Lea Barham (creator)
Crawford, John A. (advisor)
Date Issued 1981-05-07 (iso8601)
Note Graduation date: 1982
Abstract Effects of habitat and season on guild structure of avian
communities were examined for islands in the estuary zone of the
Columbia River, Oregon. Bird species were classified into guilds
according to their major food item, typical foraging substrate, and
foraging behavior. Variation in community structure indices (number of
guilds, guild diversity, evenness, bird density, and biomass) among
habitats and seasons were analyzed with multivariate analysis of
variance and discriminant function analysis. Cluster analysis was used
to examine patterns of guild distribution among habitats and seasons.
Four habitat-bird community associations (tree-shrub, upland,
beach-low marsh, and high marsh) were described based on results from
this study. High guild evenness within tree-shrub habitats during the
breeding season (spring and summer) distinguished tree-shrub bird
communities from communities within the 3 other habitats. Relatively
stable bird density within tree-shrub habitats was attributed to high
vegetation heterogeniety and later successional stage of tree-shrub
habitats.
Seasonal variation of community structure indices was greatest
within upland habitats. Comparison of seasonal patterns in number of
guilds, guild evenness, bird density, and guild composition between tree-shrub and upland habitats suggested greater stability of food
resource productivity, availability, and diversity within tree-shrub
habitats. Differences in avian community structure between the 2
terrestrial seral stages (tree-shrub and upland) were ascribed to
differences in successional stage and vegetation complexity.
High avian biomass distinguished bird communities of beach-low
marsh habitats and was probably related to high productivity typical
of estuary systems. Seasonal variation of community structure,
primarily a winter reduction in bird density, was least definitive in
beach-low marsh habitats. Lack of winter reduction in number of guilds
and seasonal changes in guild composition suggested low winter density
was related to reduced availability of food resources as affected by
tidal inundation, low temperatures, and ice on the river.
Bird communities associated with the high marsh habitat were
characterized from all other bird community-habitat associations by
greater number of guilds. Less extensive tidal inundation, greater
vegetation complexity and more edge effect in the high marsh habitat
than in beach-low marsh habitats seemed to affect greater occurrence
of terrestrial associated guilds.
Results of this study indicated description of avian community
structure on the basis of food-resource defined guilds was useful in
interpreting how environmental (habitat and season) variation may
affect bird communities. Validity of inferences from this study
requires more detailed analysis of the bird communities and their
habitats. Thus, the guild approach as used in this research is most
appropriate for preliminary examination of communities, indicating
areas where more specific study should increase understanding of the
structure and functioning of avian communities.
Genre Thesis/Dissertation
Topic Birds -- Columbia River Estuary (Or. and Wash.)
Identifier http://hdl.handle.net/1957/42062

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