Interpreting Variation in Growth of Eurasian Spoonbill Chicks: Disentangling the Effects of Age, Sex and Environment

[摘要] Chickbodyconditioncanbeasensitiveindicatoroflocalenvironmentalconditionsandhasbeenshowntobecorrelatedwithchicksurvival.Designingareliableindexofchickbodyconditionforagivenspeciesfromasinglemeasurementpointrequiresknowledgeabouttheextentofvariationinbodysize,aboutchickageandabouttherelativesensitivityofthegrowthofdifferentbiometricmeasurestovariationinenvironmentalconditions.Togainthisknowledge,wedescribesex-specificvariationingrowthofseveralmorphometricmeasuresandbodymassofEurasianSpoonbillsPlatalealeucorodia.Werepeatedlymeasured35chicksthatgrewupinsmallcoloniesontheislandofSchiermonnikoogtoderivedetailedgrowthcurvesuntilfledging(basedonthe12survivingchicks)andtoassesstheextentofreductioningrowthofstarvedchicksmeasuredatleasttwice(n=11)comparedtothosethatsurvived.Growthcurvesuntilfledgingwerecomparedwithbiometricmeasurementsoftwotofiveweekoldchicksfrom(mostly)largercoloniesofwhichhatchingdatewasaccuratelyestimated(n=631).Growthofallmeasures,excepttheeighthprimary,wassex-specific,withthemostpronouncedsexeffectontheasymptoticvaluesoftarsuslengthandbodymass:adultmaleswerepredictedtobecome17%heavierthanfemalesandtohave22%longertarsithanfemales.Bodymassandtarsusgrowthtendedtobemorereducedunderfooddeprivationthan(head-)billandeighthprimarygrowth.Asanindexofchickbodycondition,weproposetousetheproportionaldeviationinbodymassfromthepredictedbodymassforagivenageandsex.Todoso,measurementsofnearlyfledgedSpoonbillchicksshouldincludeatleasteighthprimarylengthtoestimateage,tarsuslengthtoestimatesex,andbodymassasameasurethatintegratesage,sexandenvironmentaleffects.

[学科分类] 动物科学

[关键词] Waterbirds