Over fifty percent of bird species are sexually monomorphic and the Eastern Bristlebird Dasyornis brachypterus was previously considered to be part of this majority. To test this suggestion, morphological characteristics were measured on live and preserved D. brachypterus, with sex determined genetically for 46 live individuals using a common molecular technique. Males were significantly heavier, had larger heads, longer wings and longer tails than females. Univariate sexing criteria were developed based on the differences between males and females in two of these measures, weight and head-bill length and these measures were used to sex fifteen additional birds for which sex had been determined genetically. A discriminant function was also derived from the two characters. When the discriminant function was used in conjunction with the sexing criteria, 80 % of results were consistent with molecular results, 7 % disagreed and 13 % were inconclusive. I speculate that this inaccuracy was due to juvenile males and the time of year of trapping. However, the technique can be used to sex an individual in the hand with 80% accuracy, and can therefore provide a relatively quick and inexpensive method to investigate the sex of D. brachypterus in the field; which has benefits for the active conservation of this endangered bird.

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