Associations between breeding bird abundance and stand structure in the White Mountains, New Hampshire and Maine, USA

Abstract

Assessment of faunal distribution in relation to landscape features is becoming increasingly popular. Technological advances in remote sensing have encouraged regional analyses of the distributions of terrestrial vertebrates. Comparisons of the strength of association of habitat characteristics at various scales of measurement of habitat structure are rare. We compared the associations of forest cover-type, stand size-class, and stand structure to abundance of breeding bird species in managed forest in northern New England. We surveyed breeding birds and measured stand structure in 20 stands to test the hypothesis that forest cover-type, stand size-class, and structure variables were equally associated with numbers of forest birds. We fit regression models to data from each data source to predict the log number of individuals for each species. We restricted our analyses to cover-types with > 1 size-class and to size-classes representing > 1 cover-type, and restricted our comparisons to bird species with at least 10 observations/yr for 2 yr. Of 31 bird species that met our criteria for analysis, a significant ( P < 0.05) association was detected between bird abundance and structure data for 30 species, cover-type data for 19 species, and size-class data for 10 species. Stand structure was the best predictor of bird abundance for 25 species, cover-type for 5 species, and size-class for none. Of the 14 structure variables used in the analyses, total foliage volume of large and mid-size deciduous trees, density of mid-size trees, total woody stem density, total deciduous understory volume and total volume of large conifers were most frequently important in explaining variation in species abundances. Although each species had a unique set of structural affinities, multi-layered stands are apparently more important to long-distance migrants, in general, than to resident/short distance migrants. Large-scale efforts to identify important habitats, assess degree of protection, or monitor species/habitat trends are important to conservation. For forest birds, such efforts must include estimates of the factors to which the species of concern respond. At the stand scale in New England, it seems that bird abundance is more strongly associated with forest structure than with forest cover-type or stand size-class.