Nesting Status and Chronology of Eared Grebes Along Great Salt Lake, Utah

Abstract

Eared grebes (Podiceps nigricollis) are colonial‐nesting waterbirds that breed in Canada and northern United States. Great Salt Lake (GSL), Utah, is vital to the survival of this species because all eared grebes in North America stage in the fall either on the GSL or Mono Lake, California. The importance of GSL and its surrounding wetlands for breeding eared grebes is unknown. We studied eared grebe nesting status and chronology in the freshwater wetlands around GSL and found over 4,280 nests distributed among 35 colonies during 2018 and 5,794 nests among 23 colonies during 2019. We also located the 2 largest colonies of this species ever recorded (902 and 1,492 nests). Mean clutch size differed between years and was 2.4 eggs during 2018 and 2.0 during 2019; clutch sizes were lower at GSL than in colonies located in more northern latitudes, perhaps due to a local paucity of invertebrate prey during the egg‐laying period. Grebe nests around the GSL were constructed with, and anchored to, growing Stuckenia pectinate. Eared grebes near GSL started laying eggs in the first week of June during 2018 and a week later during 2019. The number of incubated nests per colony peaked on 27 June during 2018 and 9 July during 2019. Nests continued to be incubated into August in both years. These dates are later than those reported in more‐northern colonies. The later nesting in GSL colonies could be due to the birds' need to wait for Stuckenia pectinata to form mats at the water surface. This plant species needs a water depth of 38 to 45 cm to thrive, and increasing amounts of freshwater from the GSL watershed are diverted for agriculture and human development. If this trend continues, there may not be enough water to maintain the required water depth for dense stands of Stuckenia; the loss of which may prevent the grebes from nesting. © 2021 The Wildlife Society.