A Morphometric Sex Determination Model for Adult Greater Roadrunners (Geococcyx californianus)
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2014 The Wildlife Society. Little is known of the greater roadrunner's (Geococcyx californianus; roadrunner) ecology and many demographic questions are difficult to answer because of our inability to determine adult bird sex in the field. We collected measurements from live-captured roadrunners of known sex in Fisher County, Texas, USA, and from roadrunner specimens from museums and university biological collections from 2003 to 2012 to develop a predictive logistic regression model for adult sex determination. We measured 433 adult birds of which 80% (n = 346) were randomly chosen to build potential models. Our best model included the variable estimate bill depth, which was found to be larger in males and correctly classified 80% of the birds. We validated the model with the remaining 20% of measurements (n = 87) and correctly identified the sex of 85% of the birds. Because this model incorporated roadrunners from across their range, it provides an easy, inexpensive, accurate, and field-relevant methodology for sex determination of adult roadrunners at the point of capture.
