Biology and management of eared grebes (Podiceps nigricollis ) on the Great Salt Lake, Utah

The primary objective of my research was to provided information to managers of the Great Salt Lake (GSL), Utah, on the minimum brine shrimp franciscana) requirements of eared grebes (Podiceps nigricollis). I developed and refined drive-by netting, a new technique for catching large numbers of flightless eared grebes. I used this technique to acquire eared grebes for metabolic measurements, gathering data on weight trends, and for energy consumption experiments. I measured the metabolic rates for diving bouts (0.0364 kJ g−1 h−1), resting (0.0264 kJ g−1 h−1), basal metabolism (0.0231 kJ g−1 h−1), and preening (0.0276 kJ g−1h−1 using oxygen consumption techniques. I determined the mechanical cost of transport for diving and surface swimming grebes using hydromechanical estimations of body drag. I measured both the energetic content of common prey items of eared grebes on the GSL and the assimilation efficiency of eared grebes on these prey items. I found there was little variability in the energy concentration of prey items available to eared grebes; however, the true digestibility of brine shrimp cysts was much lower (34%) than other prey items (x¯ = 88% digestible). Through behavioral observations, I determined the amount of time eared grebes spend in various activities throughout the day. Using time-energy budgets, I determined that grebes needed approximately 9,000 shrimp/day during fall 1999 and approximately 10,000 shrimp/day during fall 2000 to offset their daily energy consumption. This difference was primarily due to grebes spending more time in activities that are more energetically costly in 2000 than in 1999. I developed an energetics model based on the amount of time grebes can possibly spend foraging during the decreasing daylight hours in late fall. Based upon average weights and daylight hours in 1999 and 2000, grebes would no longer be able to gather enough adult shrimp to offset the cost of foraging when densities dropped below 0.04 shrimp per liter. These data will aid managers on the GSL in setting harvest limits on brine shrimp while maintaining, enough food resources for eared grebes staging during the fall.