Incorporating Satellite Imagery Into Analyses of Avian Distribution Patterns Across Forested Landscapes

While numerous studies have documented the relationships among bird communities and gradients of vegetation structure and composition, there is still little information regarding specific fine scale habitat associations of bird species over large areas of managed forests. Furthermore, the utility of satellite imagery for identifying influential factors on bird species occurrences and richness is rarely considered during field data collection. As part of a multidisciplinary partnership, I investigated landscape patterns of bird species occurrences and richness over a ∼400,000 ha forested region of Michigan's Upper Peninsula. Small sampling plots comparable in size to pixels of Landsat 7 ETM+ imagery (30 meter radius, n = 433) were surveyed for birds, vegetation and land cover. Bird data were also collected using 50m, 100m and unlimited distance thresholds. Landsat 7 ETM+ imagery was used to investigate spectral relationships among the data.

Several vegetation variables describing northern hardwood stands had significant independent contributions to the occurrences of 4 bird species. Some variables had both positive and negative relationships, indicating that horizontal and vertical diversity within northern hardwood stands need to be an important consideration during forest management activities. In contrast, bird species richness across the study region was highest when small areas contained large proportions of the same land cover types that dominated their surroundings. This relationship was detected through a spatially variable association between bird species richness, the Normalized Difference Vegetation Index (NDVI) and land cover types. Avian species richness estimates varied spatially in relation to NDVI and the proportion of non-deciduous land cover pixels surrounding each plot influenced the relationship. However, NDVI values were positively dependent on the proportion of deciduous forest within them. Species richness was therefore highest in deciduous forests within regions dominated by deciduous forest and the relationship was reversed in regions dominated by non-deciduous forest.

I also investigated the potential of using unclassified spectral information for predicting the distribution of three bird species. Accuracy statistics for each species were affected in different ways by the detection thresholds of point count surveys used to stratify plots into presence and absence classes and window sizes used in spectral signature development. Comparisons with rule-based maps created using the approach of Gap Analysis showed that spectral information predicted the occurrences of the investigated species better than could be done using known land cover associations.