Tf. Sutherland et al., Predation on meiofaunal and macrofaunal invertebrates by western sandpipers (Calidris mauri): evidence for dual foraging modes, MARINE BIOL, 137(5-6), 2000, pp. 983-993
Western sandpiper (Calidris mauri) predation was examined by concurrent exp
eriments and direct observations of foraging behaviour on high intertidal m
udflats of the Fraser River estuary, British Columbia. Western sandpipers f
oraged by either "pecking" on the surface (64% of observational time) or pr
obing into sediment (29%:). The first experiment (probe-mark method) consis
ted of collecting small-volume cores (21.3 cm(3)) of probed (experimental)
and non-probed (control) sediment on the tidal flat, following a 22.5-min f
eeding period. The second experiment (exclosure method) involved deploying
exclosures immediately prior to the feeding period and subsequent collectio
n of cores from inside (control) and outside (experimental) the exclosures.
Sediment cores were analysed for both macrofaunal and meiofaunal size frac
tions. Comparisons between macro- and meiofaunal invertebrate densities in
experimental and control sediments revealed significant differences, attrib
uted to shorebird predation? for both experiments. The probe-mark experimen
t detected the removal of large infaunal polychaetes (similar to 20 mm), wh
ile the exclosure experiment showed depletion of epifaunal harpacticoid cop
epods (0.063-0.5 mm). Predation on macrofaunal cumaceans was detected in bo
th experiments. Invertebrates selected by western sandpipers neither fell w
ithin traditional infaunal size classifications (macro- vs. meiofauna; 500
mum delineation) nor corresponded to the highest densities of taxa. Rather,
inference from experimental results and observations is that western sandp
ipers forage in two modes, by: (1) surface gleaning of epibenthic copepods
and cumaceans in the macro- and meiofaunal size ranges and (2) selective pr
obing for larger infauna, such as polychaetes. These findings were facilita
ted by the combination of methodologies employed.