Dietary flexibility in three representative waterbirds across salinity and depth gradients in salt ponds of San Francisco Bay |
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Authors: | J Y Takekawa A K Miles D C Tsao-Melcer D H Schoellhamer S Fregien N D Athearn |
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Institution: | (1) U. S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, USA;(2) U. S. Geological Survey, Western Ecological Research Center, Davis Field Station, 1 Shields Ave., Davis, CA 95616, USA;(3) U. S. Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA, USA |
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Abstract: | Salt evaporation ponds have existed in San Francisco Bay, California, for more than a century. In the past decade, most of
the salt ponds have been retired from production and purchased for resource conservation with a focus on tidal marsh restoration.
However, large numbers of waterbirds are found in salt ponds, especially during migration and wintering periods. The value
of these hypersaline wetlands for waterbirds is not well understood, including how different avian foraging guilds use invertebrate
prey resources at different salinities and depths. The aim of this study was to investigate the dietary flexibility of waterbirds
by examining the population number and diet of three feeding guilds across a salinity and depth gradient in former salt ponds
of the Napa-Sonoma Marshes. Although total invertebrate biomass and species richness were greater in low than high salinity
salt ponds, waterbirds fed in ponds that ranged from low (20 g l−1) to very high salinities (250 g l−1). American avocets (surface sweeper) foraged in shallow areas at pond edges and consumed a wide range of prey types (8) including
seeds at low salinity, but preferred brine flies at mid salinity (40–80 g l−1). Western sandpipers (prober) focused on exposed edges and shoal habitats and consumed only a few prey types (2–4) at both
low and mid salinities. Suitable depths for foraging were greatest for ruddy ducks (diving benthivore) that consumed a wide
variety of invertebrate taxa (5) at low salinity, but focused on fewer prey (3) at mid salinity. We found few brine shrimp,
common in higher salinity waters, in the digestive tracts of any of these species. Dietary flexibility allows different guilds
to use ponds across a range of salinities, but their foraging extent is limited by available water depths.
Guest Editors: J. John & B. Timms
Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for
Salt Lake Research |
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Keywords: | Salt ponds Diet Waterbirds San Francisco Bay |
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