Date of Award

2025

Document Type

Open Access Master's Report

Degree Name

Master of Science in Applied Ecology (MS)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Kristin Brzeski

Advisor 2

Jared Wolfe

Committee Member 1

Gordon Paterson

Abstract

Habitat loss and degradation are especially important considerations for migratory songbirds, since they depend on a variety of distinct habitats within different life phases (such as breeding, wintering, and migration) that are widely dispersed across a spatial scale. Additionally, abundance of migratory songbirds has been in severe decline, making habitat maintenance and recovery of particular interest as a research avenue. Identifying high quality habitats across a bird’s annual range is therefore of increasing importance and represents fundamental information for guiding management decision making. Free-floating metabolites found in blood are frequently used to determine short-term mass changes in birds and have been utilized to intrinsically reveal variation in habitat quality across dissimilar habitats. We collected triglyceride and β-hydroxybutyrate concentrations from songbird blood samples across seven different sites located in Michigan’s Keweenaw Peninsula across the breeding season and fall migration to better understand variation in metabolite values across life phases. Consistent with other similar studies, TRIG and BUTY values were negatively correlated, with a stronger relationship observed during fall migration. Sex-based differences in TRIG was apparent during the breeding season, with females having higher concentrations than males (p < 0.001), which is consistent with lipid allocation for egg production. Mixed linear modeling indicated that the highest variation in metabolite values was due to site, net, species, and individual differences, rather than direct relationships between TRIG and BUTY. Interpretation of TRIG and BUTY combinations during migration revealed distinct metabolic states, including energy gain, deficit, and equilibrium. Notably, high TRIG in individuals with no visible fat reserves likely reflected dietary refueling rather than fat mobilization, underscoring the importance of interpreting metabolic values in context as energetic indicators. Our results highlight the shifts in metabolite usage across life stages and suggest that variation between groups across space and time should be accounted for in future research.

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