Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Jones, Holly P.

Second Advisor

Boyce, Andy J.

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Biological Sciences

Abstract

Grassland birds are the most rapidly declining group of birds in North America due to a host of historical and recent changes to the Great Plains (Rosenberg et al., 2019; Bernath-Plaisted et al., 2023). Grassland birds evolved in a mosaic of heterogeneous habitats created by disturbance from keystone species and Indigenous peoples, and the suppression of disturbance by European settlement has resulted in more homogenous habitat and population declines in grassland birds (Knopf, 1994; Samson & Knopf, 1996; Vickery, Peter D. et al., 1998). Restoring the historical disturbance patterns and habitat heterogeneity forms the basis of management activities for grassland birds within remaining habitat (Knopf, 1994; Samson & Knopf, 1996; Vickery, Peter D. et al., 1998). Black-tailed Prairie Dogs (Cynomys ludovicianus) are a keystone species whose grazing, burrowing, and clipping on their towns is an important source of heterogeneity and disturbance for grassland birds, but their effects on bird demography are poorly understood. Further, an overall lack of demographic data for grassland bird populations limits conservation planning for them (Somershoe, 2018; Bernath-Plaisted et al., 2023). Prairie dogs may have both negative and positive effects on grassland bird fitness: prairie dogs could increase nest predation risk by attracting generalist predators and reducing nest concealment by grazing standing vegetation, while at the same time, prairie dogs could reduce nest predation risk by removing shrub cover inhabited by nest predators, diluting the proportional chance of predation through safety in numbers, and by producing information on predator activity with their alarm calls.

The goal of this dissertation was to study how Black-tailed Prairie Dogs affect grassland bird demography to better understand community ecology of the Great Plains and inform grassland bird conservation efforts. To begin, I performed a systematic literature review to synthesize current knowledge on how prairie dogs affect grassland birds and identify knowledge gaps that I would subsequently investigate. I found strong support in the literature for the ideas that prairie dogs create habitat for grassland birds that prefer early successional habitat, that the presence of prairie dogs increases beta diversity of bird communities, and that prairie dogs increase raptor abundance and diversity by serving as a high-density prey base (Chapter 1, Dreelin et al., 2025). I also identified biases and knowledge gaps in the literature, chiefly how no studies had been conducted on how prairie dogs affect songbird demography (Chapter 1, Dreelin et al., 2025).

To inform this gap, I conducted four seasons of field research on public, private, and Tribal land in north-central Montana. From 2021-2024, I monitored nest survival of Horned Larks (Eremophila alpestris) and Chestnut-collared Longspurs (Calcarius ornatus) alongside vegetation conditions on and off prairie dog towns in a natural experiment to determine how prairie dogs affect nest survival (Chapter 2). I found that while prairie dogs reduced nest vegetation height, they only affected nest visibility of longspurs, which in turn, only had a small negative effect on nest survival, and prairie dogs did not have a direct negative effect on nest survival. At the same time, drought had much more substantial effects on vegetation height and nest visibility, while suppressing prairie dog effects on nest vegetation. I also measured nestlings of both species and sampled arthropod communities on and off prairie dog towns to test whether prairie dog-mediated changes to arthropod communities influence nestling development (Chapter 3). Although arthropod prey was not more abundant on prairie dog towns, I found that increasing distance onto prairie dog towns resulted in faster nestling growth rates for Horned Larks and improved body condition at fledge for Chestnut-collared Longspurs, suggesting that prairie dog grazing creates more efficient foraging habitat. Last, I conducted paired behavioral experiments from 2023-2024 using a simulated predator and playbacks to determine whether Long-billed Curlews (Numenius americanus) eavesdrop on prairie dog alarm calls to improve their anti-predator behavior (Chapter 4, Dreelin et al, accepted). Although non-incubating curlews did not change their mobbing or alarm call behavior between control and treatment trials, exposure to prairie dog alarm calls caused incubating curlews to adopt cryptic posture on the nest when the simulated predator was three times further away.

My results demonstrate that Black-tailed Prairie Dogs have multifaceted and unique effects on the demography grassland bird species that benefit their populations in multiple ways. The findings from my field research demonstrate that the value of Black-tailed Prairie Dogs to grassland bird communities extends beyond their known contributions to creating early successional habitat and heterogeneity. Contrary to expectations, prairie dogs only had minor effects on nest predation risk. At the same time, they improved nestling development and anti-predator behavior, both of which are important indicators of survival and reproductive success. Managers seeking to promote grassland bird diversity, habitat heterogeneity, and fitness of Horned Larks, Chestnut-collared Longspurs, and Long-billed Curlews should conserve prairie dog towns where possible, and practitioners should implement policies to incentivize prairie dog retention and reduce management conflict on both public and private rangelands. Future research can build on this work by investigating how prairie dogs influence grassland bird habitat use and foraging behavior during migration and nonbreeding periods, as well as studying how certain grassland birds potentially use eavesdropping increase their survival and reproduction on prairie dog towns.

Extent

164 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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