Diets of Staging Phalaropes at Great Salt Lake, Utah

Abstract

ABSTRACTGreat Salt Lake, Utah, USA, is a critical staging area for Wilson's (Phalaropus tricolor) and red‐necked (Phalaropus lobatus) phalaropes. Both phalarope species depend upon abundant invertebrate prey in Great Salt Lake to fuel fall migrations, but the lake currently faces the threat of becoming increasingly saline due to water diversions and climate change. The lake changes may decrease the ability of Great Salt Lake to support the large populations of phalaropes that currently depend upon it. Assessing how a smaller and more saline Great Salt Lake will affect phalaropes is difficult without knowing what phalaropes are consuming during staging. We collected phalaropes from 4 different Great Salt Lake bays from 2012 through 2015 and identified prey items in their upper digestive tracts. We measured wet weights of different food items and examined total mass of food consumed by weighing gizzard contents. Phalarope diets differed across time and bays, and between phalarope species. Red‐necked phalaropes primarily consumed corixids (Corixidae) and brine fly (Ephydra hians, Ephydra cinerea) larva, pupa, and adults, whereas Wilson's phalaropes consumed brine flies, chironomids (Chironomidae) and Daphnia (Daphnia magna). Despite the abundance of brine shrimp (Artemia franciscana) in Great Salt Lake, both phalarope species rarely consumed them. Our results documented that phalaropes of Great Salt Lake are dependent for food in the less‐saline Farmington Bay and on brine flies produced in the hypersaline bays. Such information is critical for wildlife managers who are tasked with ensuring that Great Salt Lake will continue to support the large phalarope populations that depend on the lake's resources. © 2021 The Wildlife Society.