Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Wildlife Biology

Department or School/College

Ecosystem and Conservation Sciences

Committee Chair

Dr. Victoria Dreitz

Commitee Members

Dr. Lorelle Berkeley, Dr. Paul Lukacs, Dr. Jedediah Brodie

Keywords

adult density, Brewer’s sparrow, livestock grazing, nest density, nest survival, vesper sparrow

Publisher

University of Montana

Subject Categories

Biology | Population Biology | Terrestrial and Aquatic Ecology

Abstract

Sagebrush steppe is one of the most threatened ecosystems in North America. Domestic livestock grazing is the dominant land use of sagebrush steppe across the west. Rest-rotation grazing systems can be a conservation management tool, most recently, by the Natural Resource Conservation Service - Sage Grouse Initiative (SGI). The goal of SGI is to encourage private landowners to use a livestock grazing regime that maintains or improves habitat for greater sage-grouse (Centrocercus urophasianus), as well as improve rangeland productivity. Songbirds are biological indicators that can assess the health of sagebrush steppe. Avian adult density estimates are often used to assess conservation actions, given the relative ease in collecting data to inform these estimates. However, information on how conservation actions influence life histories, such as nest density and nest success are lacking, even though life histories inform abundance. My goal was to understand the relationship between adult abundance, nest density, and nest success, as well as how land management practices, in the form of grazing, influence those patterns. I investigated songbird adult densities, nest densities, and nest success over multiple breeding seasons in central Montana. I concentrate on Brewer’s sparrow (Spizella breweri), McCown’s longspur (Rhynchophanes mccownii), and vesper sparrow (Pooecetes gramineus). I explore how nest density affects nest survival and whether density dependence was present in nesting sagebrush steppe songbirds. While nest density did not appear to explain nest survival, the distance to the next nearest interspecific nest did explain nest survival for vesper sparrows, which shows some support for the presence of density dependence. Additionally, I examine the relationship between adult density and nest density on the landscape. At a local plot level, adult songbirds are often present on the landscape in higher numbers than nests. The discrepancy between adult density and nest density suggests these songbirds may not be breeding every year, as is often assumed. This study provides knowledge on population demographics of sagebrush songbirds in central Montana, their responses to current land management, and provides information that will aid in developing management strategies for these species.

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© Copyright 2019 Kayla Ann Ruth