Condition-Dependent Feather Color Change and Condition-Independent Pheomelanin Loss in the Barn Swallow

Feather coloration changes over time, but the underlying mechanisms remain poorly understood. In this study, using the reddish throat feathers of the barn swallow, Hirundo rustica, a well-known sexually selected trait, we examined whether within-season feather color change reflected the change of the major pigment, pheomelanin. As predicted, the reddish feathers faded over time, as their coloration became significantly less red with increasing intervals from the initial capture date to recapture date. Likewise, the pheomelanin content of these feathers significantly decreased with increasing intervals between captures. Neither feather color change nor pheomelanin content change depended on study year, sex, or initial capture date. However, feather color change, but not pheomelanin content change, depended on body condition at the initial capture. This condition-dependent feather color change, together with the condition-independent pheomelanin loss, indicates that seasonal change of the major pigment is insufficient to explain the observed patterns of feather color change. Future study should pay attention to additional colorants that may impact the signal honesty of animal coloration.