Does ultraviolet reflectance accentuate a sexually selected signal in terns?

Unlike the majority birds that replace their primaries once each year, most Sterna terns practice an unusual repeated wing molt, wherein a variable number of inner primaries are replaced twice or even three times in a single year. This seemingly redundant replacement of the primaries may serve as a sexually selected indicator of quality in that terns may evaluate potential mates based on the number of primaries they were able to replace twice or three times prior to the breeding season. To evaluate the potential of repeated molt as a social signal, we compared light‐reflectance curves and photon catches for new (twice‐molted) and old (once‐molted) primaries in three species of terns. We observed that old feathers reflected considerably less light across all wavelengths and found that in two of the three species examined the ultraviolet reflectance was disproportionably reduced in old feathers relative to the reduction in visible reflectance. Thus, the UV component of coloration in tern wing feathers may accentuate the difference between the new feathers generated by repeated wing molt and older, more worn feathers, thereby reinforcing a sexually selected signal of quality.