Variability of responding on a concurrent schedule as a function of body weight.

Five pigeons pecked for food reinforcers on a concurrent variable-interval one-minute, variable-interval four-minute schedule. Each bird's body weight was varied from 80% of its free-feeding weight to 95% and then by 5% steps to 110% or until weight gains ceased. The coefficient of variation, but not the standard deviation, of the daily rate of responding on each of the component schedules increased with increases in body weight.