Survival and Growth of Northern Bobwhite Chicks in Western Oklahoma JEFFREY J. LUSK 1 AND FRED S. GUTHERY Department of Forestry and Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater 74078 SCOTT A. COX Oklahoma Department of Wildlife Conservation, Rt. 1, Box 94, Forgan 73938 AND STEPHEN J. DEMASO 2 AND ALAN D. PEOPLES Oklahoma Department of Wildlife Conservation, P.O. Box 53465, Oklahoma City 73152 ABSTRACT .—Knowledge of chick ecology is essential for understanding and managing popula- tions of northern bobwhites (Colinus virginianus). We report on chick survival and growth in western Oklahoma during 1997–2002. We used Cox proportional hazard models to estimate chick survival rate. Covariates included mass at time of capture, Julian day of capture and year. Chick mass was the only significant covariate in the model. Survival depended on time since capture because survival increased with chick mass, which concomitantly increased with time since hatch. Because of the dependence of survival on chick mass, we modeled chick growth as a function of age using a logistic model (r 2 ¼ 0.98). Growth-rate was highest at day 35 post-hatch, which was around the mean capture-to-death survival time for chicks (30.0 6 4.4 d SE). Our results suggest that the 30–35-d period post-hatching is a critical period in chicks’ lives. INTRODUCTION The number of bobwhites in the autumn population is the sum of the number of adults and juveniles surviving through the breeding season. To date, adult survival has received the most research attention, and the survival rate of chicks is among the least investigated aspects of bobwhite ecology (Roseberry and Klimstra, 1984; Guthery, 2002). Knowledge of the demography of bobwhite chicks during the first few weeks of life is essential for understanding fluctuations in autumn populations. For short-lived species such as the bobwhite, population growth rate is most sensitive to changes in fecundity (Lebreton and Clobert, 1991) and, in as much as it is related to fecundity, recruitment. For bobwhites, 66% of the variation in recruitment was explained by the number of chicks hatched per hen (fecundity) (Klimstra and Roseberry, 1975). Increasing juvenile mortality by 45% (from 15 to 60% mortality) had a 2.5 3 greater impact on recruitment than a 60% increase (from 20 to 80% mortality) in adult mortality (Roseberry, 1974). Roseberry and Klimstra (1984) suggested that, because of this relationship between fecundity and recruitment, juvenile survival might play a secondary role in determining autumn population size. However, the effect of juvenile survival on recruitment and autumn population size is still considerable; Roseberry (1974) reported that fecundity and juvenile survival were equally important to recruitment. 1 Corresponding author: Department of Forestry and Natural Resources, 715 West State Street, Pfendler Hall, Purdue University, West Lafayette, Indiana 47907; e-mail: jjlusk@purdue.edu 2 Present address: Texas Parks and Wildlife Department, 4200 Smith School Road, Austin 78744 389 Am. Midl. Nat. 153:389–395