The ability of prehomeothermic chicks to thermoregulate behaviorally was studied in chicks with continuous access to heated nests, running wheels, and separate sources of high and low protein. In Experiment 1, cold-reared groups with heated or unheated transparent nests ate the same amount and selected the same dietary fractions, but chicks with heated nests ran less and grew faster. Despite this, groups maintained normal body temperatures. In Experiment 2, chicks were cold-or warm-reared with heated or unheated painted nests, or no nests. Cold-reared chicks with heated nests spent most of their time in them. They selected diets containing a higher protein : carbohydrate ratio than cold-reared chicks with unheated nests but ate less, thereby consuming less absolute protein and growing more slowly. Despite differences in growth, intake, and dietary choice, all chicks maintained normal body temperatures. These data reveal that behavioral thermoregulation has a privileged status for chicks over the first 3 weeks of life. Prehomeothermic chicks exercise complex and effective solutions to energetic challenges when offered behavioral options that simulate those available in nature.