"Mapping Density and Distribution of Ptarmigan and Arctic Ground Squirr" by Michaela L. Gustafson

Publication Date

12-2023

Date of Final Oral Examination (Defense)

10-13-2023

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Raptor Biology

Department Filter

Biology

Department

Biological Sciences

Supervisory Committee Chair

Jennyffer Cruz Bernal, Ph.D.

Supervisory Committee Member

Travis L. Booms, Ph.D.

Supervisory Committee Member

Jesse Barber, Ph.D.

Abstract

Shifting climate patterns are modifying Arctic habitats, stressing the need to understand how rapid climate and habitat changes affect Arctic trophic webs. Despite their crucial role in illuminating the impacts of Arctic changes and their ripple effects on predators, like Gyrfalcons, small Arctic primary consumers remain insufficiently studied across their range. To address this gap, I sought to estimate the distribution and abundance of Gyrfalcons' top three prey species (Willow Ptarmigan, Rock Ptarmigan, and Arctic ground squirrels) within Gyrfalcon breeding territories on the Seward Peninsula, Alaska, USA. I also aimed to discern the relationships between different habitats and species’ abundance. My methodology involved repeated counts of Willow Ptarmigan, Rock Ptarmigan and Arctic ground squirrels at 988 sites across the Seward Peninsula from May to July in 2019, 2021, and 2022. I constructed time-removal abundance models to predict distributions and abundances while evaluating crucial habitat characteristics for these Arctic prey species. Willow Ptarmigan were more abundant in areas with higher cover of tundra, shrubs, and tussock tundra, while areas with higher coverage of sparse vegetation (10-30% vegetation cover) was significant for Rock Ptarmigan and Arctic ground squirrels. Willow Ptarmigan displayed a wider distribution within Gyrfalcon breeding territories, whereas Rock Ptarmigan and Arctic ground squirrels exhibited patchier distributions with few specific areas of high abundance. My findings represent the first estimates of distribution and abundance for these vital species within Arctic trophic ecosystems on the Seward Peninsula, Alaska. Notably, Willow Ptarmigan and Arctic ground squirrels serve as ecosystem engineers, while all three species are pivotal prey for Gyrfalcons and other avian and mammalian predators. Of note, Rock Ptarmigan and Arctic ground squirrels may be more vulnerable to shrub encroachment due to a warming climate, while increased shrub growth may benefit Willow Ptarmigan as they heavily rely on shrubs for food and nesting sites. Thus, my exploration of variations in abundance of these three species holds significance in understanding the resilience of Arctic raptors and the broader Arctic trophic web.

DOI

https://doi.org/10.18122/td.2171.boisestate

Available for download on Monday, December 01, 2025

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