FILLING THE GAP: MOLTING BEHAVIOR OF COLIMA WARBLERS AND RESEARCH OPPORTUNITIES FOR UNDERSTUDIED NORTH AMERICAN SONGBIRDS

Abstract We implemented stable isotope analysis to evaluate the molt behavior of the Colima warbler (Leiothlypis crissalis), an understudied migratory songbird occurring in Mexico and recently discovered breeding in the southern part of Texas, USA. We built a geostatistical model showing variation in deuterium precipitation values (d2Hp) across a latitudinal gradient within the Colima warbler breeding range in northeastern Mexico. Then, based on stable isotope ratios of deuterium in feathers (d2Hf), we assigned wintering Colima warblers captured in Central Mexico to possible molting areas near the southwestern portion of the species' breeding range. To the best of our knowledge, this is the first field study documenting Colima warbler captures and recaptures within the Parque Ecológico de la Ciudad de México, near the mountain ranges surrounding the Basin of Mexico. Overall, our study demonstrates the potential of winter ecology fieldwork in conjunction with molecular study techniques, such as stable isotope analysis, for revealing the migratory and molting behavior of warblers with restricted distribution ranges.