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1 July 2002 A comparison of flow cytometry and the polymerase chain reaction as sexing techniques for the Wood Thrush
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Gender identification is important in demographic studies of bird populations but is difficult with monomorphic bird species. Flow cytometry, a method which estimates differences in DNA content in erythrocyte nuclei, is one potential sexing method. In another sexing method, differences between the autosomal and sex-linked (W) copies of the chromo-helicase-DNA binding (CHD) gene can be determined using the polymerase chain reaction (PCR). Frozen blood samples collected during the breeding season from known-sex adults and juvenile birds were used to test the applicability of flow cytometry and PCR as sexing methods for the Wood Thrush (Hylocichla mustelina). With flow cytometry, 86% of 14 known adults were definitively and correctly sexed. PCR correctly sexed 100% of 11 known adults. Of the 18 juveniles, 15 were sorted definitively by flow cytometry: 14 as male and one as female. PCR sexed the same 18 juveniles as 11 males and seven females, including the three juveniles that were unclassified by flow cytometry. In addition, three juveniles identified as males using flow cytometry were identified as females by PCR, among which were two individuals that consistently fell into the high end of the male genome size range. We conclude that PCR is a reliable sexing method for the Wood Thrush, but flow cytometry has limited reliability due to the lack of disparity in intergender genome size.

Robyn M. Underwood, Rebekah J. Crockett, Roland R. Roth, Calvin L. Keeler Jr., and Mark S. Parcells "A comparison of flow cytometry and the polymerase chain reaction as sexing techniques for the Wood Thrush," Journal of Field Ornithology 73(3), 239-245, (1 July 2002).
Received: 26 February 2001; Accepted: 1 August 2001; Published: 1 July 2002

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