Stable isotope analysis of an aberrant Painted Bunting (Passerina ciris) feather suggests post-molt movements

We present the first record of plumage color aberration and the occurrence of slow-growing feather tissue in the Painted Bunting (Passerina ciris), a colorful songbird breeding in the southern United States during summer and migrating to Central America in winter. We took advantage of this rare sampling opportunity and performed hydrogen stable isotope analysis on 12 cross-sections of 2 primary feathers to compare isotopic values in normal and aberrant tissue sampled from the same individual. We used feather hydrogen stable isotope variation as an informative environmental marker to track the movements of the bird across its annual cycle. Spatial probability density estimates suggest further movements after this bunting arrived at molting stopover sites in northern coastal Mexico, either migrating toward southern coastal latitudes or toward higher elevations. Although we are unable to definitively assign a cause to the aberrant feather and its slow growth rate, we highlight how combining the observation of an atypical morphological trait with a modern molecular approach offers an opportunity to advance our understanding of avian movement behavior.