Disturbance shapes avian communities on a grassland-sagebrush ecotone

Authors: DUCHARDT, COURTNEY - University Of Wyoming; Porensky, Lauren; Augustine, David; BECK, JEFFREY - University Of Wyoming

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2018
Publication Date: 9/21/2018
Citation: Duchardt, C., Porensky, L.M., Augustine, D.J., Beck, J. 2018. Disturbance shapes avian communities on a grassland-sagebrush ecotone. Ecosphere. 9:e02483. https://doi.org/10.1002/ecs2.2483.
DOI: https://doi.org/10.1002/ecs2.2483

Interpretive Summary: Grassland and sagebrush birds are among the most imperiled bird guilds in North America. As such, understanding habitat requirements of these species and how they respond to rangeland management is a critical need. While these guilds don’t typically overlap, at the transitional zone (“ecotone”) between the Great Plains and the sagebrush steppe, both bird guilds are a management priority. This may be especially challenging because grassland and sagebrush birds respond quite differently to disturbances like fire and grazing. To better understand how bird communities respond to disturbance at a grassland-sagebrush ecotone, we conducted avian surveys on and off of historic fires and active black-tailed prairie dog (Cynomys ludovicianus) colonies in northeastern Wyoming. We then modeled community structure as a function of presence of disturbance, disturbance type, vegetation structures, and abiotic features like soil composition and topography. Bird communities differed substantially between undisturbed and disturbed sites, but also differed between burned sites and prairie dog colonies. The mountain plover (Charadrius montanus), an imperiled shortgrass species, was found exclusively on prairie dog colonies and was not observed elsewhere. Mixed-grass species like grasshopper sparrows (Ammodramus savannarum) and Western meadowlark (Sturnella neglecta) reached their greatest abundance on historically burned sites, while sagebrush-dependent birds (e.g., Brewer’s sparrow; Spizella breweri) were most common on undisturbed sites. Factors like disturbance size and age also played a role in structuring avian communities. This research suggests that maintaining a mosaic of disturbance types, as well as large tracts of undisturbed habitat, is likely important maintaining populations of grassland and sagebrush birds in this landscape.

Technical Abstract: Ecotones, or transitional zones between ecosystems, are often hotspots for biodiversity and targets for conservation. Where the Great Plains meet the sagebrush (Artemisia spp.) steppe, an opportunity exists to conserve habitat for the two most imperiled avian guilds in North America, grassland and shrub-steppe birds. This ecotone creates a unique challenge with respect to the management of disturbance processes, such as fire and grazing, because grassland and sagebrush-shrubland birds respond quite dissimilarly to disturbance. To address this management challenge and maximize conservation opportunities, we examined the responses of grassland and sagebrush bird communities to disturbance at a grassland-sagebrush ecotone in northeast Wyoming. Specifically, we surveyed bird communities on active black-tailed prairie dog (Cynomys ludovicianus) colonies and historic wildfires, as well as on paired undisturbed points in 2016 and 2017. Bird community structure varied in response to both the presence and type of disturbance. Although alpha diversity of avian species was highest on undisturbed sites and historic fires, only prairie dog colonies provided breeding habitat for the imperiled shortgrass-obligate mountain plover (Charadrius montanus), and species turnover (“beta diversity”) was greatest between on-colony and off-colony points. Furthermore, bird communities were shaped by both disturbance-dependent (e.g., disturbance age) and disturbance independent (e.g., topography and soils) landscape features. Managers must balance the benefits of high species diversity in undisturbed sagebrush with habitat requirements of other imperiled species like the mountain plover. This may entail prioritizing the amount and distribution of disturbances in relation to population goals for species of conservation concern while simultaneously maintaining a mosaic of all three patch types in this landscape.