Criteria for aging and sexing New Zealand oystercatchers

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Abstract
Criteria based on external characters are presented for aging and sexing the three New Zealand species of oystercatcher, Haematopus ostralegus finschi Martens, 1897, H. unicolor Forster, 1844, and H. chathamensis Hartert, 1927. Four classes are discerned: juveniles have brown dorsal plumage, a brown iris and grey legs; second‐year birds have an orange‐red iris and pale pink legs; sub‐adults have a dull red iris and pink legs; adults have a scarlet iris and bright coral pink legs. The three species can be sexed by discriminant analysis of the sexually dimorphic characters bill length (x 1), bill length:bill depth (x 2) and bill length:bill width (x 3). Linear functions and discriminating values for predicting sex are : H. ostralegus finschi 0.46x 1+3.15x 2+2.94x 3, 77.41; H. unicolor 0.12x1+6.52x2+2.85x3 , 58.05; and H. chathamemis ‐0.93x 1+1.50x 2+7.48x 3, ‐20.86. Similarly, the sexes of immature H. ostralegus finschi can be predicted : juveniles 0.73x1+ 5.76x 2 + 3.10 x3 116.57; second‐year birds 0.57x 1+5.12x 2+ 0.98x 8, 84.84; and sub‐adults 0.55x 1+1.88x 2+ 1.08x 3, 65.90.’

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