Cumulative heatwave stress disrupts thermal homeostasis and plumage structure in a Mediterranean passerine

This dataset accompanies the manuscript “Cumulative heatwave stress disrupts thermal homeostasis and plumage structure in a Mediterranean passerine” and contains experimental data collected from captive-reared Great tits (Parus major) exposed to repeated simulated heatwaves in climate-controlled facilities. The dataset is organized into five sheets: Feather color: spectral measurements (brightness, chroma, hue indices) of contour feathers. Feather structure: morphometric and microstructural traits including feather length, barb density, and barbule density. Body mass: individual body mass recorded before and after heatwave treatments. OXY: oxidative stress markers, including d-ROMs and OXY balance values. Tb: continuous measurements of body temperature (Tb) obtained via PIT-tags, alongside ambient temperature (Ta), from which heterothermy indices (HI) and hyperthermia events were derived. Feather CORT: feather corticosterone concentrations reflecting cumulative glucocorticoid secretion during molt. These data provide an integrated view of thermoregulatory, physiological, and plumage responses to repeated sublethal heat stress in a Mediterranean songbird.