SPACE USE, HABITAT SELECTION, AND FLIGHT BEHAVIOR OF EAGLES ACROSS NORTHWESTERN NORTH AMERICA

Author

Stephen Bernard Lewis

Year of Award

2025

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Chad J. Bishop

Commitee Members

Todd E. Katzner, John S. Kimball, Brian A. Millsap, Joshua J. Millspaugh, Daniel P. Walsh

Keywords

bald eagle, behavioral state, flight behavior, golden eagle, movement, space use

Abstract

Understanding how behavioral strategies shape movement, space use, and risk exposure is essential for conserving long-lived raptors. In this dissertation, I use high-resolution GPS telemetry from bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) to examine how behavioral state, environmental context, and temporal dynamics structure raptor ecology across Alaska, British Columbia, and the western United States.

Chapter 1 used random forest classification of movement data from 43 bald eagles and 94 golden eagles to identify territorial, nesting, and floater seasons with high accuracy. Floaters comprised roughly one-third of all seasons in both species, and many individuals exhibited consistent state-specific strategies across years. These results demonstrate that floaters form a substantial, and often unrecognized, component of eagle populations, with important implications for monitoring and demographic modeling.

Chapter 2 analyzed movement and habitat selection of 82 bald eagles tracked from 2010–2024. Behavioral state was the strongest predictor of spatial behavior: territorial adults maintained small, stable home ranges, whereas floaters and immatures used much larger areas. Despite large differences in spatial extent, daily movement distances varied little among states. Resource-selection analyses revealed strong, state-specific patterns across seasons, including heightened use of coastal habitats, estuaries, tidal flats, and anthropogenic subsidies by floaters and immatures. These findings clarify divergent spatial strategies and risk profiles among behavioral states.

Chapter 3 evaluated environmental and temporal drivers of bald eagle flight altitude and implications for wildlife–aircraft strike risk using 13 years of telemetry from 47 individuals. Altitude variation was dominated by individual and annual differences, while landscape features and diel–seasonal cycles exerted modest but consistent effects. Near military airfields, eagles overlapped broadly with outer airspace surfaces but seldom entered the highest-risk zones.

Collectively, this dissertation shows that behavioral state, habitat context, and temporal dynamics strongly influence eagle ecology and management considerations across the North Pacific region.

Recommended Citation

Lewis, Stephen Bernard, "SPACE USE, HABITAT SELECTION, AND FLIGHT BEHAVIOR OF EAGLES ACROSS NORTHWESTERN NORTH AMERICA" (2025). Graduate Student Theses, Dissertations, & Professional Papers. 12583.
https://scholarworks.umt.edu/etd/12583