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Effects of Tide Stage on the Use of Salt Marshes by Wading Birds in Rhode Island
Citation:
Raposa, K. B., R. A. MCKINNEY, AND A. Beaudette. Effects of Tide Stage on the Use of Salt Marshes by Wading Birds in Rhode Island. NORTHEASTERN NATURALIST. Humboldt Field Research Institute, Steuben, ME, 16(2):209-224, (2009).
Impact/Purpose:
This paper describes the results of a study of tide stage effects on wading bird abundance, behavior, and foraging in coastal salt marshes. Results showed that birds foraged on the marshes throughout much of the tidal cycle, but engaged principally in loafing activities during mid-tides when their favored shallow-water foraging habitats were not available. Also, wading birds foraged in increasingly deeper water during rising tides rather than seeking out shallower foraging habitat. These results highlight important information to consider when evaluating landscape-scale studies that rely on instantaneous sampling of marshes to determine bird abundance, and demonstrate that more intensive sampling may be required to accurately determine wading bird use of a marsh. These results can be used to improve wading bird monitoring protocols, and to aid in the design of research aimed at quantifying resource use by wading birds.
Description:
To determine how tide stage affects wading bird abundance, behavior, and foraging in three Narragansett Bay salt marshes (RI), we conducted surveys at 10-min intervals—across the full tidal range—during six days at each marsh in July/September of 2006. The wading bird community comprised six species and was dominated by Great (72% of all observed birds) and Snowy (18%) Egrets. Birds foraged on the marshes throughout much of the tidal cycle, but engaged principally in loafing activities during mid-tides when their favored shallow-water foraging habitats were not available. Great and Snowy Egrets foraged in increasingly deeper water during rising tides rather than seeking out shallower foraging habitat. At the primary study site, total bird abundance was significantly related to tide stage based on a third degree polynomial regression (R2=0.85, F=32.44, p<0.0001); however, different patterns emerged at two other sites. These results can be used to improve wading bird monitoring protocols, and to aid in the design of research aimed at quantifying resource use by wading birds. Key words: wading bird; salt marsh; foraging habitat; tide cycle; New England; Narragansett Bay
