Avian response to changes in landscape structure in the inter-mountain west

Abstract

This research reconciled and compared two, large-area surface cover data sets to examine relationships between temporal changes in landscape structure and trends in breeding bird populations. From remotely sensed data for two time periods approximately 20 years apart, landscape structure was measured within 40 km circles around 45 USGS, Breeding Bird Survey routes in western Montana and northern Idaho. Five landscape structure indices, indicative of fragmentation, were calculated for both time periods in each circle (mean patch size, mean patch size coefficient of variation, edge, percent forest, and mean nearest neighbor distance). For each circle, metrics of change between the two time periods were correlated to individual bird population trend and to current abundance. Inconsistencies between the surface cover data sets limited the measure of landscape structure changes to only the change in forest cover. Twenty-five bird species had acceptable correlation models of response (p ≤ 0.10) to the forest component of landscape structure. Patterns of response showed some inter-mountain species were affected by forest fragmentation in similar fashion to eastern species: woodland species, predominantly migrants, exhibited a positive relationship between population trend and mean patch size and percent forest, whereas edge species exhibited a negative relationship. Similar patterns were observed in the spatial abundance of birds, calculated as a current five-year average. Overall, these results showed that useful measures of landscape change can be quantified for a large area, yielding change measures that correlated to a biological response. Results support the approach of blending remote sensing technology with ecology to conduct applied ecological research and as a possible means of monitoring entire ecosystems.