Sex-based differences in Adélie penguin (Pygoscelis adeliae) chick growth rates and diet

Sexuallysize-dimorphicspeciesmustshowsomedifferencebetweenthesexesingrowth rateand/orlengthofgrowingperiod.Suchdifferencesingrowthparameterscancausethe sexestobeimpacted byenvironmentalvariabilityindifferent ways,andunderstanding thesedifferencesallowsabetterunderstandingofpatternsinproductivitybetweenindividualsandpopulations.Weinvestigateddifferencesingrowthrateanddietbetweenmaleand femaleAdéliePenguin(Pygoscelisadeliae)chicksduringtwobreedingseasonsatCape Crozier,RossIsland,Antarctica.AdéliePenguinsareaslightlydimorphicspecies,with adultmalesaveraginglargerthanadultfemalesinmass(~11%)aswellasbill(~8%)and flipperlength(~3%).Wemeasuredmassandlengthofflipper, bill,tibiotarsus,andfootat5dayintervals for45maleand40femaleindividually-marked chicks.Chicksexwasmolecularlydeterminedfromfeathers.Weusedlinearmixedeffectsmodelstoestimatedaily growthrateasafunctionofchicksex,whilecontrollingforhatchingorder,broodsize,year, andpotentialvariationinbreedingqualitybetweenpairsofparents.Accountingforseason andhatchingorder,malechicksgainedmassanaverageof15.6gd-1 faster thanfemales. Similarly, growthinbilllengthwasfasterformales,andthecalculatedbillsizedifferenceat fledgingwassimilartothatobservedinadults. Therewasnoevidenceforsex-baseddifferencesingrowthofothermorphologicalfeatures.AdéliedietatRossIslandiscomposed almostentirely oftwospecies—onekrill(Euphausiacrystallorophias)andonefish(Pleuragrammaantarctica),withfishhavingahighercaloricvalue.Usingisotopicanalysesof feathersamples,wealsodeterminedthatmalechickswerefedahigherproportionoffish thanfemalechicks. Therelateddifferencesinprovisioningandgrowthratesofmaleand femaleoffspringprovidesagreaterunderstandingofthewaysinwhichecologicalfactors mayimpact thetwosexesdifferently