The ambiguous identity of Muscicapa trailli Audubon, and a neotype designation for Willow Flycatcher Empidonax traillii (Tyrannidae)

In 1973, a composite species long known as Traill's Flycatcher Empidonax traillii (Audubon, 1828) was split into two morphologically similar species, diagnosed primarily by vocal (song) characters: Willow Flycatcher E. traillii (Audubon) (‘Fitz-bew’) and Alder Flycatcher E. alnorum Brewster, 1895 (‘Fee-bee-o’). Application of the name E. traillii to the Willow Flycatcher, after the split, has been (and remains) disputed. The holotype (the subject of Audubon’s Plate 45) was a male collected on 17 April 1822, in Arkansas, USA, where E. traillii and E. alnorum co-occur during spring migration. There is no evidence that Audubon preserved the bird, and there is circumstantial evidence that he did not. Audubon’s holotype (male) was supposedly a breeder (not a migrant), despite the early date, because it associated with a female whose ovary was in an advanced stage of development (also not preserved). This reflects a misreading of Audubon’s account, and a misunderstanding about ovarian anatomy and development. Furthermore, some ‘types’ promoted by 20th century authors lacked valid claims to such status, and some authors (notably those who assembled evidence to support the split), led astray by a false type, applied the name E. traillii to the Alder Flycatcher. Here, to resolve two centuries of instability, I review the case and designate a data-rich neotype that preserves the modern usage of the name E. traillii (Audubon), fixing it to the Willow Flycatcher.