Biomarker of burden: feather corticosterone reflects energetic expenditure and allostatic overload in captive waterfowl

1.Allostatic load describes the interplay between energetic demand and availability and is highly context dependent, varying between seasons and life history stages. When energy demands exceed physiological set points modulated by glucocorticoid hormones, individuals may experience allostatic overload and transition between stages in sub-optimal physiological states.

2.Corticosterone, the major glucocorticoid hormone regulating energy expenditure in birds, is incorporated into growing feathers (CORTf), and it has been suggested that CORTf reflects long-term records of allostatic load during feather growth. However, relationships between allostatic load and CORTf have not been adequately evaluated. If such relationships exist, the use of CORTf to investigate cross-seasonal effects could provide novel insights into impacts of past allostatic load and/or overload events.

3.We tested whether experimental increases in daily workload during two adjacent life history stages would be refl...