Year of Award

2015

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Co-chair

David E. Naugle, Richard Hutto

Commitee Members

Mark Hebblewhite, Paul Krausman, Victoria Dreitz

Keywords

grassland songbirds, northern Great Plains, agricultural conversion, grazing management, habitat selection, conservation planning

Publisher

University of Montana

Subject Categories

Natural Resources and Conservation | Ornithology | Terrestrial and Aquatic Ecology

Abstract

Temperate grasslands are among earth’s most imperiled ecosystems. In North America, steep declines of endemic songbird populations indicate that grassland loss and degradation may be approaching critical levels. Grasslands are agricultural landscapes largely (~85%) under private ownership with little formal protection status. Remaining bird populations depend on grazing lands that have not been converted to cropland. We combine regional data from a hotspot for grassland bird diversity (northeast Montana, USA; 26,500-km2) with continental data spanning the northern Great Plains (1,000,000-km2) to evaluate how land use and management influence bird distribution and abundance. Regionally, habitat used by seven grassland specialists spanned a gradient of sparse to dense herbaceous cover. Livestock grazing influenced cover and birds but its effect was highly dependent on precipitation and soil productivity. Species distributions were variable across relatively broad spatial scales and only large landscapes (≥ 1,492-km2) were sufficient to capture maximum diversity and stability in community composition. At this scale, more grassland habitat and a wider range in herbaceous cover values were associated with high bird diversity. Sprague’s Pipit (Anthus spragueii), Baird’s Sparrow (Ammodramus bairdii), Chestnut-collared (Calcarius ornatus) and McCown’s (Rhynchophanes mccownii) longspurs were particularly sensitive to habitat amount and had reduced densities in grass-poor landscapes despite local conditions. Continentally, the breeding range of Sprague’s Pipit was restricted to areas with a high proportion of continuous grassland and a relatively cool, moist climate. Most of the pipit population (70%) relied on private lands and a quarter occurred in habitat at risk of future tillage. Spatially hierarchical models placing response to local habitat within its landscape context revealed that broad-scale patterns in land use and grassland productivity constrained the continental distribution of pipits and Chestnut-collared Longspur. Findings suggest that maintenance of large and intact grassland landscapes should be a top conservation priority. Remaining populations rely on private land, emphasizing the importance of voluntary approaches that incentivize good stewardship. Accounting for interactions between climate, soils and livestock within existing grassland landscapes may enable managers to maintain high bird diversity.

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© Copyright 2015 Marisa K. Lipsey