Predation on meiofaunal and macrofaunal invertebrates by western sandpipers (Calidris mauri): evidence for dual foraging modes |
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Authors: | T F Sutherland P C F Shepherd R W Elner |
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Institution: | (1) Canadian Wildlife Service, Pacific Wildlife Research Centre, Environment Canada, RR1, 5421 Robertson Rd, Delta, British Columbia V4K 3N2, Canada e-mail: sutherlandt@dfo-mpo.gc.ca; Fax: +1-604-6663497, CA;(2) Oceanography, Department of Earth and Ocean Sciences, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada, CA;(3) Centre for Wildlife Ecology, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada, CA |
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Abstract: | Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats
of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational
time) or probing into sediment (29%). The first experiment (probe-mark method) consisted of collecting small-volume cores
(21.2 cm3) of probed (experimental) and non-probed (control) sediment on the tidal flat, following a 22.5-min feeding period. The second
experiment (exclosure method) involved deploying exclosures immediately prior to the feeding period and subsequent collection
of cores from inside (control) and outside (experimental) the exclosures. Sediment cores were analysed for both macrofaunal
and meiofaunal size fractions. Comparisons between macro- and meiofaunal invertebrate densities in experimental and control
sediments revealed significant differences, attributed to shorebird predation, for both experiments. The probe-mark experiment
detected the removal of large infaunal polychaetes (∼ 20 mm), while the exclosure experiment showed depletion of epifaunal
harpacticoid copepods (0.063–0.5 mm). Predation on macrofaunal cumaceans was detected in both experiments. Invertebrates selected
by western sandpipers neither fell within traditional infaunal size classifications (macro- vs. meiofauna; 500 μm delineation)
nor corresponded to the highest densities of taxa. Rather, inference from experimental results and observations is that western
sandpipers forage in two modes, by: (1) surface gleaning of epibenthic copepods and cumaceans in the macro- and meiofaunal
size ranges and (2) selective probing for larger infauna, such as polychaetes. These findings were facilitated by the combination
of methodologies employed.
Received: 29 December 1999 / Accepted: 11 September 2000 |
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