Unmasking complex migration syndromes and seasonal plumage colouration in the White‐naped Xenopsaris (Xenopsaris albinucha)

Abstract

The White‐naped Xenopsaris Xenopsaris albinucha is an uncommon suboscine passerine with a disjunct distribution extending from Venezuela to the Southern Cone of South America. The ornithological literature concerning this species contains contradictory claims about potential migratory movements, although most authors consider it to be sedentary. In addition, observations of the species exhibiting a mix of male‐ and female‐like plumage during the non‐breeding season have raised the hypothesis that it may undergo seasonal colour changes – a trait often associated with migratory behaviour and seemingly uncommon in Neotropical birds. Here we use citizen science and museum specimen data to interrogate the hypotheses of migratory behaviour and seasonal phenotypic variation in the species. We found evidence for three disjunct breeding populations, of which one is resident, one is apparently partially migratory and one is fully migratory, with birds from the last two populations coming into contact during the non‐breeding season. We also found evidence for seasonal variation in the species' plumage colouration. Our results suggest that the White‐naped Xenopsaris has both resident and migratory populations and exhibits an eclipse plumage, and highlight the value of citizen science data to study seasonal variation in plumage colouration.