Tree species selection and use by foraging insectivorous passerines in a forest landscape.

摘要

Tree species were selectively used or avoided by foraging songbirds in a northern temperate mixed-wood forest. American beech (Fagus grandifolia ) was selected out of proportion to its abundance by black-throated green warbler (Dendroica virens) during 3 years of the four year study. Black-throated blue warblers (Dendroica caerulescens), American redstart (Setophaga ruticilla), and least flycatcher (Empidonax minimus) also showed selective foraging use of the American beech. Yellow birch (Betula alleghaniensis) was usually avoided by these same birds. Selective foraging occurred in sugar maple in a stand where American beech was virtually absent.; I collected data on the birds' stomach contents to ascertain that the avian diet was represented in the arthropod samples that I collected from the various tree species. The arthropod data from the birds' stomachs and from the tree foliage samples lack explicit information on relative nutrient values of prey items due to taxonomic grouping by order and a lack of information on size and weight of the prey items. Explicit and quantitative testing of hypotheses using the arthropod data is not justifiable in light of this missing information. The prevalence of this weakness in other similar studies does not justify the method. Comparison and contrast of my results and interpretations with these other studies remains a valid and informative exercise that does provide new insights into selective foraging behaviour in the context of similarly conducted programs.; The 'arthropod hypothesis' predicts that differences in arthropod density or diversity among tree species drives selective foraging behaviour. Arthropod density and diversity did not differ among tree species in a pattern that would explain the selective foraging behaviour of the focal bird species in the majority of the cases. The tree species that tended to have higher abundances of arthropods (yellow birch) was usually avoided by the foraging birds. Exceptions to this pattern suggest a role for the 'arthropod hypothesis' in limited cases.; The 'tree morphology' hypothesis focuses upon an optimal relationship between a tree species' structure and a bird's foraging behaviour. This process is probably responsible for the majority of the differential patterns of avian foraging use among tree species in this study, most notably, the selection of American beech. While this study did not explicitly test the 'tree morphology' hypothesis, my observations are consistent with this mechanism. (Abstract shortened by UMI.)