Compensatory strategies have evolved in birds to minimize the effects of poor rearing conditions on future survival and fitness. Undernourished nestlings may accelerate growth and/or development relative to age, termed compensatory growth, to achieve normal asymptotic size at the same time as well-fed chicks. While compensatory growth allows birds to fledge at a suitable size and time, it may have persistent detrimental effects on the development of complex body systems. Our study examined compensatory growth following short-term food restriction of caged groups of Zebra Finches (Taeniopygia guttata; adult breeding pair and their brood) during the nestling period, and tested for postrestriction effects on tissue maturity (indexed by body tissue water content) and adaptive immune function. Food restriction reduced nestling body mass, tarsus, and culmen growth. Rapid compensatory growth in body mass, but not in tarsus and culmen lengths, was observed upon return to ad libitum feeding of the food-restricted group. Nestlings that were raised in food-restricted treatment cages showed no significant difference in adaptive antibody response to a model antigen compared with those raised in control cages with ad libitum feeding. Reductions in tissue maturity were observed in nestlings that experienced food restriction, indicating a decoupling of chronological age and physiological age. These data provide evidence of capacity for rapid, compensatory body mass growth in nestling Zebra Finches, and suggest that the energetic costs of body growth and development are relatively larger than the costs of development of the humoral immune system.