Sarah Connors

A network of mudflats in Elkhorn Slough’s wetlands on Monterey Bay provides essential foraging and roosting habitat for shorebirds. Shorebird distribution within this habitat is highly variable, spatially and temporally, mostly because of differences in physical factors among regions, such as tidal regime, salinity, and sediment composition, that directly influence invertebrate assemblages. Such variation among sites creates a mosaic of diverse mudflat regions, including fully tidal and muted tidal mudflats. My thesis work involved evaluation of: 1) seasonal shorebird distribution patterns among the mudflat regions; 2) physical variables that characterized mudflat regions used by each shorebird species; 3) evaluation of shorebird use of muted tidal regions at high vs. low tide; and 4) changes in shorebird distribution along the main channel of Elkhorn Slough since the 1970s, when former MLML student, Bernadette Ramer, studied shorebird distribution on the main channel.

Distribution varied considerably among shorebird species. The sandpipers, Western Sandpiper, Least Sandpiper, and Dunlin, were more abundant at the upper portion of Elkhorn Slough than any other region in the study area during seasons when these species were most numerous; sediment grain size was finer in this region than in any other region in the study area. The large shorebirds were more evenly distributed throughout the main channel of the slough and other fully tidal regions in the watershed. The American Avocet and Black-necked Stilt were most abundant in muted tidal regions.

In muted tidal mudflats, sandpipers were significantly more abundant at high tide than at low tide, emphasizing the importance of these regions for feeding and roosting when fully tidal mudflats are unavailable. The American Avocet and Black-necked Stilt, larger shorebirds, were common at low tide and at high tide. Management of water level in muted tidal regions can optimize the habitat for shorebirds and other avian species.

Shorebird density changed between the 1970s and 1990s among several large shorebird species, with significantly greater density in the 1990s in the lower slough relative to the middle and upper sections. This may be the result of loss of intertidal habitat in the lower slough since the 1970s; a former Moss Landing student, Chris Malzone, found that upper intertidal habitat erosion was greatest in the lower slough. Continued loss of intertidal mudflat will result in less available foraging habitat for shorebirds. Persistence of traditional migratory stopovers and wintering grounds, such as Elkhorn Slough, is essential for shorebirds to maintain sustainable population levels.

Future research that would contribute to a better understanding of shorebird distribution in and around Elkhorn Slough includes: 1) studying invertebrate species composition in peripheral mudflat regions adjacent to the main channel of Elkhorn Slough in relation to the physical environment and shorebird use; and 2) continued monitoring of shorebird abundance and distribution in Elkhorn Slough’s wetlands to assess the impact of changes in habitat structure caused by continued erosion.

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