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Summary: J. Field Ornithol., 64(2):149-157
THE INFLUENCE OF WATER DEPTH AND SEDIMENT
TYPE ON THE FORAGING BEHAVIOR OF WHIMBRELS
CLAUDIOR. VEL,·SQUEZ1AND RENg A. NAVARRO2
InstitutodeZoologfa
Universidad Austral de Chile
Casilla 567, Valdivia, Chile
Abstract.--Prey-sizeselectionby Whimbrels(Numeniusphaeopus)feedingon an intertidal
polychaetewas investigatedto determinehow differentsubstrateconditionsaffectthe for-
agingof Whimbrelsfeedingonanintertidalmudflat.Whimbrelspreyingalmostexclusively
on largepolychaetes(Perinereisgualpensis)in an estuarinemudflatin Chile (QueuleRiver
estuary39ø20'S,73ø13'W)werestudied.Birdswerehighlyselective:the averagepreysize
foundondroppingswas53.6_ 3.7gE (n-- 914)mmtotalbodylength,and95%ofthem
werelargerthan40 mm.Whimbrelsobtainedtheirpreyalmostexclusivelybydeepprobing
becauselargewormswerefoundmainlyat depthsbelow3 cmin thesubstrate.Observations
of feedingWhimbrelswere madein five sedimentconditions:(1) shallowwater, sediment
coveredby a 2-10 cmwaterlayer;(2) waterfilm, sedimentcoveredby a waterfilm ·2 cm
deep;(3) wetsandwith nowaterlayer;(4) drysand;and(5) mud.Foragingwassignificantly
more successfulin sandy areas than in muddy areas. This result correspondedwith an
observedlower densityof large polychaetes(·40 mm) in the mud. Within sandyareas
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