Year of Award

2021

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Wildlife Biology

Department or School/College

Wildlife Biology Program

Committee Chair

Victoria J. Dreitz

Commitee Members

Patrick Donnelly, Winsor Lowe, John Kimball

Keywords

white-faced ibis, Plegadis chihi, wetlands, landscape change, remote sensing, waterbirds

Subject Categories

Other Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology

Abstract

Wetlands structure landscape biodiversity by providing critical habitat to numerous fish and wildlife species. However, climate change, growing human populations, and shifting land use practices strain limited water supplies that sustain wetlands in the semi-arid western US. Conserving a wetland network with prominent value to wildlife is paramount to ensure future security of habitat and ecosystem processes. Here, I use white-faced ibis (Plegadis chihi; hereafter ‘ibis’) breeding colonies as a model system to identify and monitor a landscape-scale wetland network across the semi-arid western US. Ibis serve an important role in marking ecologically important wetland networks because they require a wide range of wetland habitats near colony locations for nesting and foraging. My analysis encompasses 153 breeding colonies in eight regions, derived from ecoregions, located on private and public lands. I evaluate long- term (1988-2020) patterns of wetland availability at ibis breeding colonies using surface water as a proxy for wetland flooding. Surface water trends are examined based on individual colony, region, ownership, hydrology (i.e. annual duration of wetland flooding), and wetland types (e.g. flood-irrigated agriculture, managed wetlands). To identify landscape drivers influencing flooding patterns, I link long-term trends to regional climate and anthropogenic factors. Analysis shows that approximately 60% of individual colony locations experienced wetland drying, and 5 of the 8 regions showed significant declines in wetland availability. Snow-water equivalent, daily minimum temperature, and irrigation were prevalent drivers of wetland trends. Publicly managed wildlife refuges, a central component to the colony network, were specifically impacted by patterns of wetland drying. These areas provide important over-water nesting locations in semi- permanent wetlands. Additionally, declines in flood-irrigated agriculture impacted adjacent ibis colonies through reduced foraging habitat. While underlying mechanisms influencing individual wetland sites are complex, pervasive drying of nesting and foraging habitat imperils the wetland network resiliency. Regional coordination and private-public partnerships are key to the long- term viability of a wetland network that benefits ibis and numerous other wetland-dependent species.

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