Habitat Choice and Niche Characteristics Under Poor Food Conditions. A Study on Migratory Nearctic Shorebirds in the Intertidal Flats of Brazil

摘要

ThetidalflatsoftheBragantinianPeninsulainthetropicalpartofBrazilharbourwinteringandmigratorynearcticshorebirdsinveryhighdensities,whereasthebenthicfoodsupplyisverylow.In2001and2002astudywasconductedonthehabitatchoiceanddistributionofshorebirdstoinvestigatetheformationofnichesandthespatialdistributionundertheconstraintofalimitedfoodsupply.Weshowedthatshorebirddensitieswerenotcorrelatedwitharangeofabioticvariablesorwithpreydensitywithinsites,butthatbetweensitesbirdstendedtoselectsiteswithpeakpreydensities.Twoforagingguildsweredifferentiated:WhimbrelNumeniusphaeopus,WilletTringasemipalmataandShort-billedDowitcherLimnodromusgriseuspreferredtoforageinthewateroronwetsandatthewater'sedge;whileRedKnotCalidriscanutus,GreyPloverPluvialissquatarola,RuddyTurnstoneArenariainterpres,SemipalmatedSandpiperCalidrispusillaandSemipalmatedPloverCharadriussemipalmatus,werefoundpredominantlyondrysubstrate.Althoughthebirdsshowedspecies-specificpreferencesforcharacteristicsdefiningmicrohabitats,nicheswerebroadlyoverlapping.Theresultsofourstudysuggestthat,incaseofaverylowfoodsupply,individualsmightnotbeabletoreacttocompetitionbynichesegregationbutmightbeforcedtofeedinabroadrangeofavailableniches.