Despite the hemispheric importance of Great Salt Lake (GSL) as a staging area for migratory birds, little is known about the resources that GSL provides to these birds, or how changes to the GSL ecosystem might impact the avian community. Three species of migratory waterbirds that stage at GSL are Wilson’s phalaropes (Phalaropus tricolor), red-necked phalaropes (Phalaropus lobatus), and eared grebes (Podiceps nigricollis). My objective for this research was to study the impacts of prey availability on the staging ecology of these species. In Chapter 2, I examined the use of GSL habitats by both species of phalaropes. In the high-salinity bays of GSL, phalaropes were most strongly associated with shallow water. In the low-salinity bay, there were no strong associations between phalarope presence and particular habitat characteristics. In Chapter 3, I analyzed the behaviors of phalaropes relative to prey densities. Phalaropes commonly foraged in Carrington Bay, which had the highest densities of brine fly (Ephydridae) adults, and in Farmington Bay, which had high densities of benthic macroinvertebrates. Foraging behavior differed between Wilson’s and red-necked phalaropes, with Wilson’s phalaropes spinning more often than red-necked phalaropes. In Chapter 4, I examined interannual and nightly variations in eared grebe fall migration departures in relation to prey availability and environmental conditions. Eared grebes began migration relatively early when lake temperatures were relatively warm, densities of brine shrimp (Artemia franciscana) adults were high, and densities of brine shrimp cysts were low. The likelihood that eared grebes would depart on a given night was positively associated with the average barometric pressure 12 hours prior to sunset. The resources provided by GSL support substantial proportions of the staging populations of phalaropes and eared grebes. Management efforts should seek to maintain the habitats and resources needed by phalaropes and eared grebes at GSL. Future large-scale diversions of freshwater may threaten GSL’s suitability as a staging area for these birds.

Eared Grebes (Podiceps nigricollis) are migratory birds that build their nests over water and in large groups called colonies. Their typical breeding range is in central southern Canada and northern United States; however, a previously uncertain number of Eared Grebes (grebes) also nest around the Great Salt Lake (GSL), Utah, at the southern edge of their breeding range. Little is known about the habitat requirements for grebe nesting colonies at such low latitudes and if they are different from colonies found elsewhere. My objectives for this research were to determine the status of the grebe nesting population as well as their habitat characteristics along the GSL in freshwater wetlands. I found over 4,280 grebe nests distributed among 35 colonies. Grebes built nests by mounding submerged aquatic vegetation (SAV) beginning the first week of June. The results from my habitat study show that grebes prefer to nest in areas with an average water depth of 48 cm, high invertebrate density, and abundant areas of floating SAV. Water depth and vegetation type at colony sites as well as timing of nesting and average number of eggs per nest of GSL colonies differed from colonies located at more northern latitudes. The differences in nesting could be attributed to the need to wait for SAV to grow and form mats on the water’s surface, or a need to wait for their food source to reach harvestable size. After grebes leave their nesting grounds, they stop at the GSL where they prepare for their final migration southward by consuming their fill of brine shrimp (Artemia franciscana). Brine shrimp are tiny invertebrates that are well-adapted to salty environments; they produce hard-walled eggs called cysts which are of great economic value and are commercially harvested from the GSL. I compared cyst viability, which is the percentage of cysts in a condition conducive to hatching, for cysts that had passed through the digestive tract of grebes and cysts samples obtained from the GSL. Only 30% of the cysts that had passed through grebes were viable, whereas 63% of cysts from the GSL were viable.