Juvenile whooping cranes (Grus americana) raised for wild release were found to have an increased incidence of rib fractures at fledging in 2017 compared with the previous 16 years. Serum analysis showed 30-day-old juveniles in 2017 (n = 12) had significantly lower 25-hydroxyvitamin D3 and significantly higher parathyroid hormone concentrations than juveniles in 2010 (n = 6) with no history of rib fractures. Increased serum parathyroid hormone concentrations in the 2017 juveniles persisted to fledging age. Review of dietary and environmental management revealed that juveniles in 2017 were provided a commercial diet with a lower, and perhaps suboptimal, calcium:phosphorus ratio and experienced reduced time outdoors in the first month after hatch, presumably resulting in less ultraviolet B radiation exposure. Mild hyperparathyroidism in precocial whooping cranes may result when dietary constraints and/or outdoor access is compromised and manifest as rib fractures in the absence of traumatic injury.