The study of moult has received increased scientific attention due to its interdependence with other life-history aspects and its value as a reliable proxy of a bird's fitness. Here, we perform a detailed description of post-juvenile partial moult of a Red Crossbill Loxia curvirostra population exploiting Scots Pine Pinus sylvestris forests in the Pyrenees, southern Europe, with data from more than 1700 moult records. Crossbills within the tested population had replaced all or most median coverts and the six innermost greater coverts (GCs; 70–87%), decreasing outwards. Just 10% of the birds had renewed GC1. Tertials were renewed in half the cases and, exceptionally, some tail feathers, secondaries, primaries or primary coverts were renewed (less than 10%). Post-juvenile partial moults were more extensive in Pyrenean crossbills compared to crossbills in northern Europe, and in females compared to males. Among males, there were differences in moult extent dependent on colour, from greater to lesser extent: patchy, red, orange and yellow. Several factors could underlie these differences, such as climate, food availability or stability (explaining latitudinal differences), hormonal and sexual selection processes (explaining sex-dependent variation), hatching date or oxidative stress associated with the expression of colour patterns.