Date of Award:

5-2016

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Michael R. Conover

Committee

Michael R. Conover

Committee

John A. Bissonette

Committee

Frank P. Howe

Committee

David N. Koons

Committee

Wayne A. Wurtsbaugh

Abstract

Millions of birds use Great Salt Lake, Utah, during their migrations every year. While many of the birds use the shorelines and wetlands around Great Salt Lake, there are three migratory species that use the open waters of Great Salt Lake: Wilson's phalaropes (Phalaropus tricolor), red-necked phalaropes (Phalaropus lobatus), and eared grebes (Podiceps nigricollis). Eared grebes feed primarily on brine shrimp (Artemia fanciscana), while phalaropes are thought to consume brine flies (Ephydridae) and brackish-water aquatic invertebrates. Despite the reliance of phalaropes and eared grebes on the invertebrate prey of Great Salt Lake, little is known about how prey availability affects the ecology of these birds at Great Salt Lake, or about how changes to the Great Salt Lake ecosystem might impact migratory birds. I studied the relationship of prey availability with phalarope habitat use, phalarope foraging behavior, and eared grebe fall migration departure.

Phalaropes used different resources in different bays of Great Salt Lake, and for different purposes. In high-salinity bays, phalarope flocks were most common in shallow water. In a low-salinity bay, phalaropes were not strongly associated with any particular habitat characteristic. Phalaropes were most likely to feed and search for prey in two particular bays, Carrington and Farmington. Farmington Bay had the high densities of aquatic invertebrates, while Carrington Bay had the most brine fly adults.

Eared grebes migrated from Great Salt Lake earlier in years when the lake temperature was high, densities of brine shrimp adults were high, and densities of brine shrimp cysts were low. On any given night, eared grebes were more likely to migrate if the average barometric pressure was high for 12 hours before typical departure time.

Phalaropes and eared grebes require reliable food resources so they can gain mass before migration each year. A substantial proportion of these species' populations rely on Great Salt Lake to provide those resources. Management efforts should maintain the habitats and resources that support phalarope and eared grebes at Great Salt Lake. Future large-scale diversions of freshwater may threaten these birds, because insufficient freshwater inflow can lead to decreased foraging habitat and decreased prey availability.

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