Date of Award
Doctor of Philosophy (PhD)
Scott R. McWilliams
Managing oxidative stress is an important physiological function for all aerobic organisms, particularly during periods of prolonged high metabolic activity, such as long-distance migration. However, no previous study has investigated the oxidative status of songbirds at different stages of migration, whether that oxidative status depends on the condition of the birds, how birds use their condition in concert with access to free water to make stopover decisions, or the effects of oxidative challenges like flight on subsequent reproduction. Additionally, scientists undertaking such research are commonly expected to disseminate their results as a Broader Impact of their studies - typically to secure research funding - and often struggle to do so, given that they are not usually trained in non-technical communication or public engagement. In this dissertation, I introduce the fundamentals of oxidative balance in flying songbirds (Chapter 1), discuss physiological factors affecting the condition and behavior of migratory songbirds on stopover (Chapters 2 and 3), describe the impact of dietary antioxidants and flight exercise on songbird reproduction (Chapter 4), and present a framework of guiding principles to help researchers communicate their science (Chapter 5). Development of this framework influenced the style and approach of the dissertation as a whole, with each chapter’s organization and figure design benefiting from lessons transferrable from communication with non-scientist audiences to communication with professional peers.
To investigate the relationship between energy stores and oxidative status of long-distance migratory birds on stopover, I drew blood samples from two species of Neotropical migrant (Blackpoll Warbler, Setophaga striata, and Red-eyed Vireo, Vireo olivaceus) with differing migration strategies during autumn migration on Block Island, USA, and a species of trans-Saharan migrant (Garden Warbler, Sylvia borin) during spring migration on the island of Ponza, Italy; I found fat stores to be positively correlated with circulating antioxidant capacity in Blackpoll Warblers and Red-eyed Vireos and positively correlated with circulating lipid oxidation levels in all three species. Among Garden Warblers, oxidative damage levels decreased with time on stopover (up to 8 nights). Thus, the physiological strategy of migrating songbirds appears to be to (1) build prophylactic antioxidant capacity in concert with fuel stores at stopover sites before a long-distance flight, and (2) repair oxidative damage while refueling at stopover sites after long-distance flight.
To assess the contribution of free water to migratory birds’ stopover decisions, I captured 61 free-living Garden Warblers in spring at a frequently used stopover site in the Mediterranean Sea, housed them with or without drinking water, and measured nocturnal restlessness (Zugunruhe) in relation to energy stores at capture; water-deprived birds of high fat score showed the highest Zugunruhe activity, suggesting that individuals with higher fat scores might be expected, regardless of flight muscle size, to depart a dry stopover site more readily than a site with freely available water.
To examine how songbirds use nutrition to manage trade-offs in antioxidant allocation between endurance flight and subsequent reproduction, I performed a controlled experiment with Zebra Finches (Taeniopygia guttata), using four treatment groups of birds that either were or were not provided a water- and lipid-soluble antioxidant-supplemented diet and were or were not trained to perform daily endurance flight for 6 weeks before breeding; I found that exercised birds had higher oxidative damage levels than non-exercised birds after flight training, supplementation with water-soluble antioxidants decreased the deposition of lipid-soluble antioxidants to eggs and yolk size, and flight exercise lowered deposition of lutein but not vitamin E to eggs. These results mechanistically demonstrate potential carry-over effects of nutrition and exertion on the capacity of songbirds to provision eggs with important nutrients after long-distance flights.
To address how the potential for “impact” of varied Broader Impacts dissemination activities can be critically assessed during proposal writing and peer review, I combined the experiences of successful practitioners with communication theory to synthesize a five-point framework; this “Broader Impacts Impact Framework” summarizes best practices in communication and outreach, can be easily used by scientists during proposal writing and review, and focuses on five main factors: who, why, what, how, and with whom.
Skrip, Megan M., "Oxidative State of Songbirds During Migration and Best Practices to Communicate the Science" (2016). Open Access Dissertations. Paper 424.