Date of Graduation

1988

Document Type

Dissertation/Thesis

Abstract

This study examines the dietary ecology of a guild of 9 canopy dwelling, foliage gleaning, insectivorous birds in a West Virginia deciduous forest. The types, numbers, and distribution of prey available in the forest canopy were determined by direct observation of canopy arthropods and estimation of arthropod abundance on a per leaf surface area basis. Different prey were associated with different substrates and other locations within the forest canopy. Birds "preferred" Lepidoptera larvae, Coleoptera, and Homoptera, and large prey. Spring defoliating caterpillars, an important food source, were most common during the early breeding season (May) and declined thereafter. Birds responded to declining numbers of caterpillars by switching to other prey. Bird diets were closely tied to foraging behavior, which determines in part the substrates in the canopy that are examined for prey and the types of prey they most frequently encounter and are adept at catching. At most times, the guild exhibited high levels of resource partitioning (i.e. had different diets), as predicted by competition theory. An important exception was early in the breeding season, when many species ate newly emerged larval Lepidoptera. The response of birds to emerging caterpillars was similar to that of birds to insect outbreaks reported elsewhere. Dietary responses and level of resource partitioning in this and other studies are summarized using a model incorporating resource abundance and habitat complexity. Correlations between trophic structures (body weight and bill length) and prey length were generally strong, although these were weakened sometimes by omitting some bird species or prey types from analysis. Ratios of larger to smaller species for trophic structures failed to demonstrate a constant value. Principal components ordinations isolated most species (or groups) from other species (or groups) both dietarily and morphologically. Canonical correlation analysis showed a significant correlation between diet and morphology. However, these results were often due to only one or several morphologically unique species that ate unique prey, rather than from patterns that permeated the entire guild. It was concluded that bird diets are too variable to show strong correlations with morphology at a single point in time.

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