Fuelling Rates by Spring-Staging Ruffs Philomachus pugnax in Southern Belarus

摘要

OnthefloodplainmeadowsofthePripyatRiverinsouthernBelarus,RuffsPhilomachuspugnaxformconcentrationsofupto30,000individualsduringspringmigration.TheRuffsreplenishtheirenergyreservesbeforecontinuingtheirnorthwardsmigration.Overeightspringseasons,betweenlateMarchandmiddleMay2001a€“2008,wemeasuredthebodymassincreaseinasampleof2839adultand342immaturemales,and2058adultand136immaturefemalescaughtinthemiddlePripyatnearTurov.Bodymassincreasedintwophasesinthespringseason,risingslowlyinthefirstandfasterinthesecondphase;thebreakpointdatebetweenthetwophasesdifferedbetweenthesexes(24Apriland3May,respectively)andshowedlessvariationinfemalesthaninmales.Adultmalesgainedanaverageof1.1g/dayinthefirstphaseandlater2.4g/day.Immaturemalesgained0.39g/dayintheearlierphaseand1.7g/daylater.Adultfemalesgainedonaverage0.56g/dayintheearlyphaseand1.22g/daylater.Inimmaturefemalestherateofbodymassgainwasnotsignificant.Therateofbodymassincreasevariedamongyears.Thewaterlevelhadanegativeimpactonthebodymassincreaseinfemales,butnotinmales.Presumably,malesarelessaffectedbythewaterlevelastheyhavemuchlongerlegsandareabletoforageindeeperwater.Accordingtotheestimatedflightranges,bothsexeswereabletoreachatleastthebreedinggroundsinthewesternpartofSiberiainonenonstopflight,exceptinyearswithhigherwaterlevels.ThemiddlePripyatisprobablythelaststopoversitebeforetheirbreedinggroundsforatleastaportionofthesebirds.