Foraging behavior of Red-necked (Phalaropus lobatus) and Wilson's (P. tricolor) phalaropes on Great Salt Lake, Utah | Comportamiento de forrajeo de los falaropos Phalaropus lobatus y P. tricolor en Great Salt Lake, Utah
2022
Frank, Maureen G. | Conover, Michael R.
Great Salt Lake (GSL) is a critical staging area for 2 species of phalaropes: Wilson's (Phalaropus tricolor) and Red-necked (P. lobatus). Both rely on the abundant invertebrate prey at GSL to fuel their fall migrations to Central and South America, but little is known about where phalaropes forage on GSL, what foraging methods are used, or what variables influence their foraging decisions. During 2014 and 2015, the frequency of specific foraging behaviors by phalaropes differed by GSL bays; surface picking was the most common foraging behavior (≥50%) on Carrington and Gilbert bays while spinning was the most common on Farmington Bay. Most (60%) Red-necked Phalaropes used surface picking for foraging compared to 32% of Wilson's Phalaropes. Spinning behavior to upwell prey was more common in Wilson's Phalaropes (used by 19% of foraging birds) than Red-necked Phalaropes (3%). The proportion of phalaropes in a flock that were foraging was positively associated with biomass of invertebrate prey at the flock's location. Most (64%) of the phalarope flocks were on Farmington Bay, and 75% of phalaropes in this bay were foraging, compared to 41% of birds on Gilbert Bay. Thus, Farmington Bay is particularly important for hundreds of thousands of Red-necked and Wilson's phalaropes that stage on GSL for 4 months during each summer. Farmington Bay is brackish, shallow, and depends on the Jordan River for its freshwater. The future of this water source, and therefore Farmington Bay itself, is uncertain because of future diversions by humans and longer droughts predicted from climate change.
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