Wetland habitat use, protein sources for reproduction, and nest habitat selection by sea ducks facing rapid change in the Alaskan Arctic

Author

Micah Miller, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2023

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Lovvorn, James

Abstract

Migratory animals face numerous challenges that are often exacerbated by climate change. In the Arctic, where climate change is occurring at 4x the average global rate, species must adapt rapidly to novel conditions. I studied four species of sea ducks (Long-tailed Ducks Clangula hyemalis and Steller’s Polysticta stelleri, Spectacled Somateria fischeri, and King Eiders S. spectabilis), of which Steller’s and Spectacled Eiders are federally Threatened, and all are well below historic population sizes. I conducted three studies to assess how female sea ducks interact with their habitats between arrival on the breeding grounds and nesting. First, I assessed patterns of occurrence within diverse tundra wetland types by female sea ducks, in relation to three metrics of wetland resource availability: wetland surface area and biomass in benthic cores and emergent sweeps separately. I also monitored activity budgets of female sea ducks. Wetlands containing the emergent grass Arctophila fulva were highly selected for by all species relative to the wetland surface area and biomasses of prey, while large lakes, streams, and wetlands lacking Arctophila were avoided. Most time was allocated towards foraging or loafing, emphasizing the importance of energy acquisition during this transitional time period following migration and prior to nesting. Wetlands selected for broadly across species are under threat as climate change reduces the prevalence of these wetland types on the landscape, requiring adaptation to such novel conditions. My second study assessed how sea ducks rely upon prey resources within tundra wetlands, and upon stored tissues acquired in marine habitats. Female sea ducks must both produce eggs and sustain themselves throughout a ~30-day period from egg-laying through hatch, with potentially different nutrient sources for each aspect of the reproductive process. I sampled stable isotopes of proteins in egg membranes (reproductive endpoint) and in red blood cells (body maintenance endpoint), which I modeled relative to stable isotopes in a suite of prey taxa from freshwater tundra ponds and marine habitats. Across all four species, most proteins came from tundra wetlands (≥ 89% of modeled protein sources) for egg production. Smaller-bodied long-tailed Ducks and Steller’s Eiders relied heavily on the local environment for body maintenance and survival (red blood cells) during incubation, but larger Spectacled and King Eiders only gained ~60% of proteins locally, relying on the remaining 40% from body tissues acquired previously from marine habitats. Local wetlands provided 60-99% of proteins for female sea ducks. Freshwater habitats in which sea ducks forage warrant protection, and conservation for some species requires interagency cooperation across tundra, freshwater wetlands, and marine habitats. My third study assessed patterns of nest site selection across species, years, and spatial scales. How females choose nest sites has major implications for population processes. Decisions integrate information across spatial scales for each component of habitat a hen considers. I used boosted regression trees (a machine learning technique) to model suitability of nesting habitat for 414 variables of habitat features at six spatial scales. Social association with other ducks were highly important in determining suitability. Suitable habitat varied spatiotemporally among species, but the relative amount of suitable habitat was consistent across years for each species. Conservation for suitable habitat must include broad areas to incorporate interannual variability. Through these three studies, I assessed the relative use of; importance of; and reliance upon various wetland types, the relative importance of marine versus freshwater nutrients for reproduction, and the factors driving nest site selection in a guild of sea ducks facing imminent climate change.