Responses to increased costs of activity during incubation in a songbird with female-only incubation: does feather colour signal coping ability?

Individuals differ in their ability to cope with energetically demanding situations while caring for the current brood, and they can signal this ability by their colouration. We examined the impact of handicapping (clipping of wing and tail feathers) on an energetically demanding care behaviour (incubation) in female Great Tits (Parus major). We hypothesised that the intensity of carotenoid-based breast feather colouration signals the ability to cope with impaired flight ability and the consequent increased energetic demands. If this is the case, females with more intensely coloured feathers should cope better with the handicap compared with less intensely coloured females, i.e. the impact of handicapping on mass loss and nest attentiveness should be negatively correlated with colouration. Handicapped females lost more weight than control females but did not decrease nest attentiveness to a greater extent, suggesting that females take the costs of handicapping on themselves. Females in poor condition were more severely influenced by handicapping. Intensity of female breast feather colouration did not correlate with either change in nest attentiveness or body mass loss during incubation. Intensity of breast feather colouration therefore does not appear to signal female ability to cope with this energetically demanding situation during incubation.