Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Degree Statement

Master of Science in Biological Science

Department

Department of Biology and Wildlife

Committee Chair

Muehlbauer, Jeffrey

Committee Member

Hagelin, Julie

Committee Member

Breed, Greg

Table of Contents

Chapter 1: Introduction

Chapter 2: Methodology

2.1 C. cooperi breeding phenology and ambient insect community

2.2 Aquatic insect emergence modeling

2.3 Predicted impacts of warming

Chapter 3: Results

3.1 Breeding phenology

3.2 Water temperature regimes

3.3 Aquatic insect emergence and availability

Chapter 4: Discussion

4.1 Current breeding phenology of C. cooperi

4.3 Implications for C. cooperi fitness

4.4 Conclusion.

Abstract

Migratory insectivorous birds are an increasingly threatened group worldwide. These birds rely on an ephemeral resource of insects during a short window in which they arrive at breeding territories to rear young. Climate change has the potential to create a phenological mismatch between the timing of bird breeding and the availability of key insect prey. This study investigates the potential for such a phenological mismatch in a population of olive-sided flycatchers (Contopus cooperi). We used data on breeding phenologies and the composition of insect communities around nests in three regions of Alaska, Anchorage, Fairbanks, and Tetlin National Wildlife Refuge, to compare C. cooperi breeding stage timing to the emergence of adult aquatic insects. These insects are a potentially important prey resource that may provide highly unsaturated fatty acids (HUFAs), which are hypothesized to be essential for chick development in other aerial insectivore species and may also serve as migration fuel. We used generalized additive mixed models (GAMMs) to build aquatic insect emergence schedules representative of these regions within Alaska. These schedules were compared to maximum observed regional breeding stage windows for C. cooperi to evaluate the magnitude of phenological mismatch. Distinct breeding phenologies were exhibited by C. cooperi in each region, although mean timing for each breeding stage was not significantly different, indicating most individuals across these regions breed on a similar timeline. Emergence schedules of aquatic insects in Anchorage and Fairbanks were found to shift earlier under forecast warming scenarios for 2033 and 2043. Peak insect emergence in Anchorage occurring during laying, and its projected shift earlier into the laying stage with warming, reduces the availability of aquatic insects later into the breeding season. This limited availability may be mitigated by the high magnitude of daily emergence from streams in Anchorage. C. cooperi in Fairbanks displayed higher phenological alignment with local aquatic insect prey, with peak emergence always estimated to occur during an overlap of fledging and departure, and a smaller peak occurring during an overlap of hatching and fledging. Chick development and migration for C. cooperi in Fairbanks may still be impacted by projected declines in emergence late in the season, and the lower magnitudes of both emergence and availability of aquatic prey directly at nests.

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