Influence of Forest Vegetation Structure on Avian Community Composition in West-Central Idaho

Abstract

Locally derived information is needed if management guidelines intended to improve wildlife habitat are to be relevant, reliable, and applicable. Within the Intermountain West, few studies have examined habitat relationships of forest songbirds in mixed‐conifer forests. During 1996–1997, we studied breeding bird communities in a mixed‐conifer forest in west‐central Idaho, USA, to describe how relative avian abundance was related to forest structure. Our study objectives were to 1) describe bird use of 3 distinct forest age‐classes, 2) identify groups of species that expressed similar relationships with forest structural attributes, and 3) model species‐specific bird—habitat relationships. We sampled 46 study sites (forest stands) classified into 1 of 3 common “vegetation growth stages” (seral stages): 1) shrub/seedling/sapling (n = 15 stands), 2) small tree (n = 16 stands), and 3) old growth (n = 15 stands). In each stand we surveyed breeding birds using fixed‐radius point counts and measured forest structure at each point‐count location. Of 30 species examined, the relative abundance of 10 differed among vegetation growth stages. Differences in stand structure were reflected by several strong gradients of vegetation structure and composition (e.g., canopy cover, diameter of large trees, snag density, and stump density) across vegetation growth stages. We used cluster analysis to establish novel information about how birds responded to these gradients and identified 3 distinct bird assemblages: forest generalists, early seral specialists, and mid‐ to late‐seral specialists. Habitat models derived from multiple linear regression revealed that canopy cover was the best predictor of variation in abundance for numerous bird species. We conclude that changes in the amount of overstory cover will have the greatest influence on birds. Where canopy cover is reduced below, or increased above, a threshold level of approximately 25–40% cover, we predict that occurrence or density of some breeding birds will change. Our habitat models suggest that Townsend's warbler (Dendroica townsendi), red‐breasted nuthatch (Sitta canadensis), and brown creeper (Certhia americana) would respond negatively to reductions in canopy cover; chipping sparrow (Spizella passerina), dusky flycatcher (Empidonax oberholseri), and warbling vireo (Vireo gilvus) would respond positively. This type of information will contribute to regional planning processes by allowing species “trade‐offs” to be assessed under different forest management scenarios.

A Meta‐Analysis of Bird Responses to Uniform Partial Harvesting across North America

“…This species nests under the loose bark of snags and forages for insects in bark crevices of large trees. Its abundance has been linked to the availability of large trees (Hansen et al 1995) and snags (Sallabanks et al 2006), both of which are strongly affected by harvesting. Likewise, Ovenbirds were highly sensitive to harvesting in this study and others (Guénette & Villard 2005; Harrison et al 2005).…”

Sound settlement: noise surpasses land cover in explaining breeding habitat selection of secondary cavity‐nesting birds

“…Although we have shown species-specific variation in nest box occupancy, there is often a management imperative to understand how environmental factors and management practices influence several species within a community simultaneously (Palmer et al 1997, Trzcinski et al 1999, Sallabanks et al 2006, Eigenbrod et al 2008). Our combined analyses show that noise is an important predictor of occupancy among secondary cavity-nesting birds, exceeding all other variables in this analyses.…”

Modeling the effects of environmental disturbance on wildlife communities: avian responses to prescribed fire

“…That is, hierarchical models provide a framework for carrying-out so-called ''composite analyses'' of data on many species (Sauer and Link 2002). Formulating management guidelines for every individual species is not always a viable option (Franklin 1993, Sallabanks et al 2006. Formulating management guidelines for every individual species is not always a viable option (Franklin 1993, Sallabanks et al 2006.…”

“…Currently, assessments of avian responses to environmental disturbances, such as fire, are often made by summarizing individual species responses (Bock and Block et al 2005, Smucker et al 2005, Kotliar et al 2007 or using ordination techniques such as redundancy analysis and detrended correspondence analysis (Morissette et al 2002, Cleary et al 2007. Researchers attempting to identify individual bird species-habitat relationships in forests with and without fire often cannot assess populations of rare or elusive species, and generally limit their analyses to species with some minimum number of detections (Morrissette et al 2002, Smucker et al 2005, Sallabanks et al 2006, Schwab et al 2006, Kotliar et al 2007). However, less common species may be of most interest to land managers.…”