Dietary antioxidants in life-history trade-offs: differential effects of a-tocopherol supplementation on blue tit Cyanistes caeruleus mothers and offspring during reproduction

α-Tocopherol is assumed to be the most biologically active dietary antioxidant in vivo, but despite its potential importance little is known about its impacts on wild birds. Reproduction is presumed to be costly for parents through several routes, including increased oxidative stress, particularly for bird species producing large clutches. If dietary antioxidants can ameliorate oxidative stress associated with reproduction, mothers supplemented with dietary antioxidants are predicted to be in improved condition and/or invest more resources in reproduction than controls. We provided adult blue tit pairs with an α-tocopherol-enriched or control food supplement during nest building and egg laying, then cross-fostered half broods between treatment groups to test the theory that α-tocopherol-supplemented mothers would invest more in self-maintenance or reproduction than controls. We found that α-tocopherol supplementation had no effect on the maternal condition or reproductive investment. However, effects on nestlings were evident: nestlings from α-tocopherol-supplemented mothers were smaller at hatching. There was no effect on chick fledging mass, fledging success or lipid peroxidation, but the catch-up growth exhibited by chicks from α-tocopherol-supplemented parents may be considered costly. Thus, our results do not provide evidence for a benefit of maternal α-tocopherol supplementation at a biologically relevant dose on either themselves or their offspring. We discuss our findings in terms of ongoing research on the multifaceted roles that dietary ‘antioxidants’ can have in vivo, and the issues of disentangling their impacts on physiology and behaviour in the wild.