Effects of landscape change on golden-winged and blue-winged warblers in Michigan

The objective of this research was to compare changes in landscapes over time where Golden-winged and Blue-winged Warblers were present and absent in the lower peninsula of Michigan. To do this, the landscape composition (land cover types within the landscape) and landscape structure (degree of fragmentation of land cover types) along Breeding Bird Survey (BBS) routes where both species were present were examined and compared to routes where they were absent in 1978, 1993, and 2000. Differences in landscape composition and structure around 46 BBS routes were compared using classified land cover data from 1978, 1993, and 2000. A GIS was used to create a 400-meter buffer around BBS routes. Total area and area-perimeter ratios for 12 landscape composition and 12 landscape structure variables were calculated within each buffered area. Principal components analysis explained covariation patterns across multiple landscape composition and structure variables. Analysis of variance was used to test the significance of each principal component. Results show that both Golden-winged and Blue-winged Warblers are moving northward. Potential causes of range shift for these species may be due to increased human influence and increased fragmentation of land cover types they find favorable creating an overall more homogeneous landscape.