We examined the relationship of trends in fall–spring mass of 330 Northern Bobwhites (Colinus virginianus) with photoperiod, air temperature, energy requirements, and supplemental feeding in the Texas Panhandle during 2000–2003. Mass of bobwhites increased from September to December, at which point it peaked and then decreased through March. Mean monthly mass was negatively correlated with photoperiod (r =−0.89) and temperature (r =−0.79) and positively correlated with energy required (r = 0.79; estimated using air temperature). From September to March, bobwhites occupying areas where supplemental feed was provided (n = 246) were greater in mass (x̄ = 193.4 g, 95% CL = 191.6–195.1) than bobwhites in areas without supplemental feed (x̄ = 186.5 g, 95% CL = 184.0–189.0, n = 84), but mean monthly mass was different only during November (x̄ = 197.8 g, 95% CL = 195.3–200.3 for food-supplemented; x̄ = 188.0 g, 95% CL = 185.0– 191.0 for unsupplemented). Abiotic factors, such as photoperiod and temperature, are confounding factors when attempting to explain fall and winter trends of bobwhite mass. Temporal changes in activities (daily foraging, nocturnal roosting) and their energetic costs (e.g., thermoregulation) also complicate issues of trends in mass.