90 Great Salt Lake Phalaropes and Eared Grebes: Factors Affecting Survey Counts and Distributions

Faculty Mentor: Jody Reimer (Biological Sciences, University of Utah)

Each year, Great Salt Lake (GSL) provides habitat for millions of birds at various periods of their migration (Tavernia et al., 2021). However, declining lake elevation and increased salinity due to climate change and water diversions pose a threat to these birds (Meng, 2019; Conover & Bell, 2020). Eared Grebes (Podiceps nigricollis), Wilson’s Phalaropes (Phalaropus tricolor), and Red-necked Phalaropes (Phalaropus lobatus) are some of the most abundant species at GSL during the staging period of their migrations (GSLEP, 2024). Eared Grebes primarily feed on brine shrimp (Artemia franciscana) and phalaropes primarily feed on brine flies (Ephydra species). In 1982, Great Salt Lake Ecosystem Program (GSLEP) began conducting survey counts of waterbirds in GSL. The available data from these surveys show bird numbers by species or foraging group as well as the survey area or sighting location. Despite extensive data collection of both bird counts and environmental factors, the influence of the environment on these waterbird populations has not yet been examined. This research aims to use linear regression to model how GSL environmental conditions influence phalarope and Eared Grebe numbers. Environmental covariates include precipitation, temperature, lake elevation, salinity, river inflow, and relevant food sources, all of which are hypothesized to impact shorebird populations at GSL (Senner et al., 2018; Frank & Conover, 2023, 2019; Tavernia et al, 2021). The regression models thus far show a significant negative correlation between average annual temperature and average total phalarope count for a given year, but no other statistically significant correlations have yet been found. Next, additional regressions will be performed taking into account more in-depth information on phalarope and grebe biology.

This research also investigated the spatial distribution of Eared Grebes through creation of a heatmap as shown in Figure 1. The Eared Grebe survey data used for the heatmap was sent by GSLEP (John Neill, personal communication, 2025). Bird counts were conducted as part of an aerial transect survey in the fall of each year. Photos were taken at consistent intervals along each transect, and then grebes were counted from the photos. The variables used to create the heatmap were transect start and end coordinates, transect numbering (for the transects themselves as well as the numbers corresponding to each photo), photo numbers, and grebe counts for each photo, in addition to the constant flight speed and time interval between photos. Based on the heatmap images and the biology of Eared Grebes, it appears that grebe distribution is primarily influenced by access to food sources.

High density areas were typically located close to shore; either the shore of an island or the perimeter shoreline of the lake. These areas were most frequently located around Fremont Island (especially south of the island), on the west or south sides of Antelope Island, and east of Stansbury Island. For the surveys that had conditions listed, the high density areas most often had calm conditions, ripples, or slight waves. Areas with high grebe counts also frequently mentioned the presence of microbialites or brine shrimp cyst streaks as well as shallow water nearby. Overall, considering the year-to-year differences in transect locations, the sites with the most grebes did not appear to vary significantly by year.

Densities in the year 2000 were highest just east of Stansbury Island. Transects covered Fremont Island, Stansbury Island, and the northwest corner of the South Arm of GSL.

The 2010 survey shows the highest densities in the southernmost part of the lake near I-80. Transects were primarily placed along the shorelines of the South Arm and next to the islands.

The highest densities in the 2022 survey were found south of Fremont Island and just west of the northern part of Antelope Island. Transects covered nearly the entire South Arm. Figure 1. Eared Grebe density heatmaps for the 2000, 2010, and 2022 aerial transect surveys. The left images show densities corresponding to the color scale. The right images show the placement of the transects that were flown during surveying.

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