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Gender identification of Caspian Terns using external morphology and discriminant function analysis

Wilson Journal of Ornithology

By:
, , , , and
DOI: 10.1676/07-061.1

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Abstract

Caspian Tern (Sterna caspia) plumage characteristics are sexually monochromatic and gender cannot easily be distinguished in the field without extensive behavioral observations. We assessed sexual size dimorphism and developed a discriminant function to assign gender in Caspian Terns based on external morphology. We collected and measured Caspian Terns in San Francisco Bay, California, and confirmed their gender based on necropsy and genetic analysis. Of the eight morphological measurements we examined, only bill depth at the gonys and head plus bill length differed between males and females with males being larger than females. A discriminant function using both bill depth at the gonys and head plus bill length accurately assigned gender of 83% of terns for which gender was known. We improved the accuracy of our discriminant function to 90% by excluding individuals that had less than a 75% posterior probability of correctly being assigned to gender. Caspian Terns showed little sexual size dimorphism in many morphometries, but our results indicate they can be reliably assigned to gender in the field using two morphological measurements.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Gender identification of Caspian Terns using external morphology and discriminant function analysis
Series title:
Wilson Journal of Ornithology
DOI:
10.1676/07-061.1
Volume
120
Issue:
2
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Wilson Journal of Ornithology
First page:
378
Last page:
383