Songbird Relationships to Shrub-Steppe Ecological Site Characteristics

Abstract

Rangeland managers are often faced with the complex challenge of managing sites for multiple uses and for the diverse interests of stakeholders. Standardized monitoring methods that can be used and understood by different agencies and stakeholders would aid management for long-term sustainability of rangelands. In the United States, federal land management agencies have recently based their assessments of rangeland health and integrity on state-and-transition models to consider management trajectories. Ecological sites provide a foundation for these efforts but have not been used to address wildlife habitat. Habitat preferences are documented for North American shrub-steppe songbirds but have yet to be related to ecological sites and site characteristics. We characterized ecological sites at Browns Park National Wildlife Refuge, Colorado, using established rangeland monitoring methods to test whether 1) songbird species density and diversity differ among adjacent shrub-steppe ecological sites and 2) quantifiable ecological site characteristics could be identified that account for significant variation in songbird density and diversity. Vegetation structure (represented as basal and canopy gaps, cover, height, and shrub density) differentiated the four ecological sites and was related to songbird density and diversity. Sage sparrows (Amphispiza belli) and vesper sparrows (Pooecetes gramineu) selected habitat based on horizontal characteristics of vegetation structure, such as basal and canopy gap and plant species cover. Brewer’s sparrow (Spizella breweri), lark sparrow (Chondestes grammacus), and songbird diversity were more strongly related to vegetation structure of the plant communities than to plant composition. Our results support use of ecological sites as management units to characterize songbird habitat given that songbird density and diversity were related to site vegetation characteristics. By incorporating basal and canopy gap, height, plant cover, and shrub density monitoring methods into ecological site descriptions, managers would be provided with additional tools to assist in differentiating songbird habitat.