Accuracy for Determining Sex of White-Tailed Deer Fetuses

Explanations for variation in fetal sex ratio are needed to better understand the white-tailed deer (Odocoileus virginianus) life-history strategy. Sex determination in fetal white-tailed deer is often based on external morphology and previous studies indicate that fetal sex does not become morphologically distinct until 63-69 days postconception. Until the advent of molecular techniques, there was no means to evaluate observer accuracy or to determine whether fetal sexing is feasible at <63 days postconception. We collected fetuses from wild deer in Mississippi, USA during spring 2008 (n = 55) and 2009 (n = 88) and measured fetal sex classification among 3 groups of observers with differing levels of experience: an inexperienced group (n = 31), an experienced group (n = 3), and a wildlife biologist group (n = 12). We then determined fetal sex using sex-linked genetic markers and modeled observer accuracy using logistic regression. The inexperienced group required fetuses aged 63 days, 67 days, and 75 days old to correctly classify with 90%, 95%, and 99% accuracy, respectively. The experienced group correctly sexed fetuses at 54 days, 55 days, and 56 days old with 90%, 95%, and 99% accuracy, respectively. The wildlife biologists correctly sexed fetuses at 55 days, 57 days, and 59 days old with 90%, 95%, and 99% accuracy, respectively. Our study was the first to use known-sex fetuses to estimate observer accuracy of fetal white-tailed deer at various ages. Our results suggest training observers to recognize fetal tissue development can improve classification accuracy. (C) 2011 The Wildlife Society.