Sexual Dimorphism and use of Morphological Measurements to Sex Adults, Immatures and Chicks of Rockhopper Penguins

摘要

Followingrecentphylogeneticwork,RockhopperPenguinsweresuggestedtoconsistoftwoorthreespecies.FortheSouthernRockhopperPenguinEudyptesc.chrysocome,sexualdimorphismhasnotbeenstudiedindetail,andonlyafewpreviousstudiesonpenguinshaveinvestigatedsexualdimorphisminimmaturesandchicks.Usingdataintheliterature,weexaminedwhetherthesexualdimorphismofadultsvariesamongthethreetaxaofRockhopperPenguinsandthenweinvestigatedthemostreliablemeasurementstosexadultRockhopperPenguins.Weobservedthatbilllengthisthemostusefulmeasurementtoseparatemalesfromfemales.Toallowforsexdiscriminationinthefield,wealsoexaminedalargedatasetofSouthernRockhopperPenguinsfromNewIsland,FalklandIslands,includingadultssexedviaobservationofbehaviour,andimmaturesandchickssexedgenetically.Wefoundthatmaleadultsandimmatureswerelargerthanfemalesinbilllengthandbilldepthand,toalesserdegree,inflipperlengths.Wethusderiveddiscriminantfunctionsfrombilllengthandbilldepthandcorrectlysexed96.2%ofadultsand91.8%ofimmatures.Innewlyhatchedchicks,maleshadalongerbillthanfemales,butsexingwasonlysuccessfulfor63.5%ofhatchlings.Justbeforethecr?¨cheage(18and19days)andafterthepre-fledgingmoult(55daysandolder),allmorphologicalmeasurementsofchicksweresignificantlydifferentbetweensexes,andsexdeterminationwassuccessfulfor68.2%and84.3%ofchicksintheseagegroups,respectively.Consistentlyamongagegroups,billlengthwasthemostdimorphiccharacterinthispopulation.