[Tweeters] oystercatcher sexing

Ian Paulsen birdbooker at zipcon.net
Mon Mar 28 17:24:53 PDT 2011

Here's the abstract to the Black Oystercatcher sexing
article that Denny Granstrand mentioned on tweeters yesterday:

Secrets in the eyes of Black Oystercatchers: a new sexing technique
Brian M. Guzzetti et al. Journal of Field Ornithology
Volume 79, Issue 2, pages 215223, June 2008.

ABSTRACT Sexing oystercatchers in the field is difficult because males and
females have identical plumage and are similar in size. Although Black
Oystercatchers (Haematopus bachmani) are sexually dimorphic, using
morphology to determine sex requires either capturing both pair members
for comparison or using discriminant analyses to assign sex
probabilistically based on morphometric traits. All adult Black
Oystercatchers have bright yellow eyes, but some of them have dark specks,
or eye flecks, in their irides. We hypothesized that this easily
observable trait was sex-linked and could be used as a novel diagnostic
tool for identifying sex. To test this, we compared data for
oystercatchers from genetic molecular markers (CHD-W/CHD-Z and
HINT-W/HINT-Z), morphometric analyses, and eye-fleck category (full eye
flecks, slight eye flecks, and no eye flecks). Compared to molecular
markers, we found that discriminant analyses based on morphological
characteristics yielded variable results that were confounded by
geographical differences in morphology. However, we found that eye flecks
were sex-linked. Using an eye-fleck model where all females have full eye
flecks and males have either slight eye flecks or no eye flecks, we
correctly assigned the sex of 117 of 125 (94%) oystercatchers. Using
discriminant analysis based on morphological characteristics, we correctly
assigned the sex of 105 of 119 (88%) birds. Using the eye-fleck technique
for sexing Black Oystercatchers may be preferable for some investigators
because it is as accurate as discriminant analysis based on morphology and
does not require capturing the birds.


Ian Paulsen
Bainbridge Island, WA, USA
Visit my BIRDBOOKER REPORT blog here:

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