Morphological Sex Determination in Black-faced Cormorants (Phalacrocorax fuscescens)

Julie Riordan, Gregory Johnston

    Research output: Contribution to journalArticle

    3 Citations (Scopus)

    Abstract

    Black-faced Cormorants (Phalacrocorax fuscescens) are endemic to marine environments in southern Australia and little is known of their biology. Development of a reliable and practical method for sexing adult birds in the field is necessary to aid research into their behavior and life-history. Eleven measurements from museum specimens (27 male; 31 female) were used to document sexual dimorphism in Black-faced Cormorants using discriminant function analyses (DFA). A simultaneous DFA correctly sexed 81% of birds, while a stepwise DFA correctly sexed 85% of birds based on two measurements (bill length and mid tail length). However, terminal wear of the retrices make this measurement unreliable. A logistic regression using bill length correctly predicted the sex of 78% of individuals. Black-faced Cormorants with a bill ≤ 76 mm long are likely female and ≥ 77 mm long are likely male, therefore providing a reliable method for assigning sex in the field. Black-faced Cormorants exhibit the same pattern of sexual dimorphism found in all other cormorants studied to date: males are larger, more robust and have a longer bill compared to the smaller, relatively gracile and shorter-billed females. The use of this general rule to assign sex to adult Black-faced Cormorants was confirmed through the observation of mating behavior. Therefore, this study provides a dependable and practicable technique for assigning sex in the field without the need to capture birds and disturb their behavior.

    Original languageEnglish
    Pages (from-to)94-101
    Number of pages8
    JournalWATERBIRDS
    Volume36
    Issue number1
    DOIs
    Publication statusPublished - Mar 2013

    Keywords

    • Black-faced Cormorants
    • discriminant function
    • morphology
    • Phalacrocorax fuscescens
    • sexual dimorphism

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