IMPACTS OF CONIFER REMOVAL ON SONGBIRD DENSITY, REPRODUCTIVE OUTPUT, AND HABITAT SELECTION

Author

Elise Catherine Zarri

Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

Wildlife Biology Program

Committee Chair

Thomas Martin

Commitee Members

Mark Hebblewhite, David Naugle, Angela Luis, John Maron

Publisher

University of Montana

Abstract

Restoration of anthropogenically altered habitats is vital to protect biodiversity and prevent species extinction as landscapes are increasingly altered, degraded, and lost. However, restoration is often done without a full understanding of its impact on biological communities. Lack of knowledge can lead to unintended negative consequences for some species restoration was intended to benefit. Woody plant encroachment is a form of habitat alteration occurring in grasslands and shrublands around the globe, driven by anthropogenic shifts in disturbance regimes. One example is conifer expansion into historically widespread sagebrush communities. Sagebrush restoration through conifer removal has become a common strategy to aid declining sagebrush associated wildlife. Removal is often done to improve habitat quality for the Greater Sage-Grouse, which is expected to be an umbrella species for other sagebrush wildlife. However, responses of species other than sage-grouse have not been quantified. I investigated demographic rates, habitat selection, and indirect effects of predation risk on an assemblage of sagebrush-obligate, shrubland generalist and woodland associated songbirds using a control-impact design in Medicine Lodge Valley, Montana. Species responses to conifer removal were aligned with their habitat associations. Sagebrush-obligate species, including Sage Thrashers and Brewer’s Sparrows, as well as a grassland species, the Vesper Sparrow, benefited from conifer removal through increased abundance and fledgling production. Brewer’s Sparrows experienced lower nest predation rates and produced larger nestlings in removal areas. White-crowned Sparrows and Green-tailed Towhees occurred at lower densities and produced fewer fledglings where conifers were removed but were flexible in their habitat selection across the ecotone. Two woodland-associated species, Chipping Sparrows and Dark-eyed Juncos were nearly absent from removal areas and preferred areas with high tree cover even within non-removal areas. This study did not reveal any major unintended consequences of conifer removal, but the detailed information provided about species responses and habitat needs will aid the success of future projects. While habitat restoration is urgently needed in many areas, clear understanding of species and community responses beforehand will help ensure effective restoration.

Recommended Citation

Zarri, Elise Catherine, "IMPACTS OF CONIFER REMOVAL ON SONGBIRD DENSITY, REPRODUCTIVE OUTPUT, AND HABITAT SELECTION" (2023). Graduate Student Theses, Dissertations, & Professional Papers. 12249.
https://scholarworks.umt.edu/etd/12249