Data from: Antioxidant capacity is repeatable across years but does not consistently correlate with a marker of peroxidation in a free-living passerine bird.

We investigated the repeatability, within-individual variation and correlation across different conditions of two plasmatic markers of the oxidative balance (reactive oxygen metabolites or ROMs, a marker of lipid and protein peroxidation, and non-enzymatic antioxidant defences measured through the OXY test) in 1108 samples from 635 free-living adult collared flycatchers (Ficedula albicollis). We sought to manipulate energy constraints by increasing wing load in 2012 and 2013 and by providing additional food in 2014. More information can be found in the related research article, published in Journal of Comparative Physiology B (DOI 10.1007/s00360-019-01211-1).