Relationships between hedgerow characteristics and bird communities:: a multivariate approach

Abstract

Fifty 100m hedge transects were selected within 10km of Durham City, North England. The bird community of the hedge transects was censused six times between May and July, and characteristics of the hedge and surrounding landscape were recorded. The data was analysed using multivariate methods to determine the importance of the microstructure of the hedge in relation to aspects of the bird community. Stepwise Multiple Regression selected the scores of the first axis of a Detrended Correspondance Analysis of shrub abundance data (related to the height and width of the hedge) as the best predictor of Bird species richness and density. Individual species were related to different aspects of the hedge microstructure. The use of transformed independent data improved the predictive value of most of these relationships. A Detrended Correspondance Analysis found that major source of variation in the bird species abundances was due to the number of trees in the hedge. Canonical Correspondance Analysis was used to analyse how a community responds to a set of external factors. The CANOCO first axis was related to an increase in the area of nearby woodland in the positive end and an increase in the number of trees in the negative end. The position of the species scores in relation to these environmental gradients was analysed. The habitat preferences of 4 common species of bird was explored using "sector” analysis, whereby the mean density of the species is plotted against the major sources of variation in the environmental variables, different habitat preferences between species are apparent. The importance of trees to the bird community was elucidated using Linear Discriminant Analysis. The analysis was carried out with hedges with no trees and hedges with 3 or more trees as the two a priori groups. Eighty-three percent of the sites were placed in the correct groups, using 14 common bird species as variables. The importance of the microstructure of the hedge to the bird community is discussed.