Grasshopper Sparrow Distribution, Habitat Associations, and Use as an Indicator Species for Grassland Birds in Southwestern Minnesota.

摘要

Reductions in grassland habitat due to agricultural conversion have caused severe declines in populations of many grassland bird species. Effective grassland bird conservation requires efficient use of limited funding. Techniques advocated by conservationists include: 1) focusing management activities on a single indicator species that represents the habitat and management requirements of other species, 2) managing existing preserved habitat for appropriate vegetation structure to ensure desired population responses, and 3) identifying areas of high value for species of interest through remotely sensed data. In Minnesota, the Grasshopper Sparrow (Ammodramus savannarum) has been identified as a species of conservation interest and potential management indicator species. My objectives were to: 1) assess the extent to which the Grasshopper Sparrow and seven other passerines might serve as grassland bird indicators, 2) identify local-scale habitat associations of these species, and 3) develop and assess the suitability of landscape-scale species distribution models for the Grasshopper Sparrow. To address these objectives I conducted bird and vegetation surveys on 71 grassland sites in southwestern Minnesota during 2013--2014, examined patterns of community composition and species-specific habitat associations, and modeled Grasshopper Sparrow density. I found that the Grasshopper Sparrow could reasonably be used as a management indicator for five of seven grassland species. Inclusion of a second indicator species could improve representation of the entire group of species. Grasshopper Sparrow density was positively associated with distance to trees and negatively associated with vegetation height, vegetation density, and percent tree cover. Grasshopper Sparrow density also exhibited nonlinear relationships with litter and percentages of shrub, dead vegetation, and bare ground cover. Judicious selection of explanatory variables offered an efficient approach to determination of species' habitat requirements and predicting their occurrences. Finally, using both local-scale habitat and remotely sensed landscape variables produced a better model than using variables at either scale alone.