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6 March 2023 A new genus for Thalurania ridgwayi (Trochilidae)
George Sangster, Jimmy Gaudin, Karl-L. Schuchmann
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Mexican Woodnymph Thalurania ridgwayi was long included in the genus Thalurania. A previously published molecular phylogenetic study found that this species is in fact sister to the genus Eupherusa. We discuss whether ridgwayi is better lumped with Eupherusa or placed in a different genus, and consider that the latter arrangement best reflects the multiple morphological differences between ridgwayi and Eupherusa. Consequently, we describe a new genus for ridgwayi.

Mexican Woodnymph Thalurania ridgwayi Nelson, 1900, was described as a species based on a single specimen collected in Jalisco, western Mexico. It was lumped with Fork-tailed Woodnymph T. furcata (J. F. Gmelin, 1788) and treated as a subspecies of the latter by Peters (1945) without any taxonomic discussion. Subsequently, it was regarded as a subspecies of Crowned Woodnymph T. colombica (Bourcier, 1843) (AOU 1983) until Escalante-Pliego & Peterson (1992) raised it to species level based on differences in plumage colour and pattern from Mesoamerican members of T. colombica.

Phylogenetic analysis of multilocus molecular data has placed T. ridgwayi as sister to the four species of Eupherusa Gould, 1857, and distant from other species of Thalurania Gould, 1848 (McGuire et al. 2014). This was surprising given the morphological similarities of T. ridgwayi to other Thalurania (del Hoyo et al. 1999), including the green throat and chest, dark belly and bright blue-violet crown. However, the phylogenetic evidence clearly demonstrates that T. ridgwayi cannot be maintained in Thalurania because this would result in a polyphyletic taxon.

There are two main ways to reconcile the close relationship of T. ridgwayi to Eupherusa with the requirement that all genera are monophyletic. First, T. ridgwayi might be transferred to Eupherusa (Stiles et al. 2017, Chesser et al. 2020). Stiles et al. (2017) argued that the blue crown of male T. ridgwayi is quite similar to that of Blue-capped Hummingbird E. cyanophrys Rowley & Orr, 1964. However, a blue crown does not clearly group T. ridgwayi with Eupherusa because three of the four species of Eupherusa lack a blue crown and several other species of emerald hummingbirds (Trochilini) also have a blue crown (e.g., Violet-capped Hummingbird Goldmania violiceps, Violet-capped Woodnymph Thalurania glaucopis, Blue-headed Sapphire Chrysuronia grayi, Andean Emerald Uranomitra franciae, Long-tailed Sabrewing Pampa curvipennis excellens). A blue crown has evidently evolved multiple times independently in emerald hummingbirds and carries little weight in grouping taxa into genera. Stiles et al. (2017: 406) also stated that ‘the blackish underparts’ of male T. ridgwayi are shared with male Black-bellied Hummingbird E. nigriventris Lawrence, 1868. We disagree that this is a shared character state because, unlike male E. nigriventris, male T. ridgwayi actually has most of the underparts dusky green, not black (Howell & Webb 1995), and only part of the belly is black (Escalante-Pliego & Peterson 1992). Stiles et al. (2017: 406) further stated that females of T. ridgwayi and Eupherusa share grey underparts and ‘differ mainly in tail patterns’. However, grey underparts occur in the females of several other species of emerald hummingbirds (e.g., Golden-crowned Emerald Cynanthus auriceps, Napo Sabrewing Campylopterus villaviscensio, Antillean Crested Hummingbird Orthorhyncus cristatus, White-vented Plumeleteer Chalybura buffonii, Long-tailed Woodnymph Thalurania watertonii) and the presence of grey underparts is clearly also not a reliable way to define genera. Importantly, females of T. ridgwayi do not differ mainly in tail pattern from Eupherusa but also, clearly, by the absence of red on the secondaries and tertials (present in Eupherusa). Overall, the arguments listed to lump T. ridgwayi with Eupherusa are not compelling.

Figure 1.

External morphology of males (upper row) and females (lower row) of ‘Thaluraniaridgwayi and the four species of Eupherusa, illustrating the forked blue tail, lack of a distinct red patch on the secondaries and tertials, and lack of white in the tail of the former. Illustrations by Norman Arlott (used with permission from Birds of the world / Cornell Lab of Ornithology).


The second way to address the distant relationship of T. ridgwayi to the morphologically similar Thalurania and its close relationship to the morphologically different Eupherusa is to place T. ridgwayi in a monotypic genus. Whether or not to ‘chop up’ a dichotomous phylogeny into two genera has often depended on the extent of the morphological differences between groups. There are many examples of avian sister taxa that are recognised as different genera explicitly or implicitly based on morphology, including Tetrao / Lyrurus (Phasianidae), Rostratula / Nycticryphes (Rostratulidae), Sterna / Thalasseus (Sternidae), Fulmarus / Macronectes (Procellariidae), Phyllaemulor / Nyctibius (Nyctibiidae), Eudyptes / Megadyptes (Spheniscidae), Drymornis / Drymotoxeres (Dendrocolaptidae), Parus / Pseudopodoces (Paridae) and Cardellina / Myioborus (Parulidae). Sister genera in Trochilini also differ by multiple morphological character states, including Abeillia / Klais, Anthocephala / Stephanoxis, and Leucippus / Phaeochroa.

In this case, there are multiple prominent differences between T. ridgwayi and the four species of Eupherusa (Fig. 1). T. ridgwayi (i) lacks red on the wing (clearly present on the secondaries and tertials in both male and female Eupherusa), (ii) has a forked tail (square in Eupherusa), which is (iii) mainly blue (black in Eupherusa) and (iv) lacks white on the outer rectrices in males (present and extensive in Eupherusa).

We believe the differences between T. ridgwayi and the four species of Eupherusa are best reflected taxonomically by the recognition of two genera. T. ridgwayi shares no unique character state with the four species of Eupherusa and its inclusion in Eupherusa would make that genus unnecessarily heterogenous. Eupherusa would no longer be diagnosable by any single character, unlike the present classification in which Eupherusa can be distinguished from all other emeralds by the presence of red on the tertials. We feel that the multiple clear differences between T. ridgwayi and the four Eupherusa strongly outweigh the debatable similarities between T. ridgwayi and individual species of Eupherusa, and therefore separate genera are warranted. Thus, a separate genus name is required for T. ridgwayi. Because no such name is available, we propose:

Dicranurania, new genus

  • Type species.—Thalurania ridgwayi Nelson, 1900.

  • Diagnosis.—Small hummingbird (size 9–10 cm) most closely related to Eupherusa. Tail forked (square in Eupherusa). Tail blue (black in Eupherusa), lacking white on the outer tail feathers in males (present and extensive in Eupherusa). Secondaries and tertials lack red (present in Eupherusa).

  • Included taxa.—D. ridgwayi is the only member of the genus.

  • Etymology.—Derived from the Greek δικρανον (dicranon) meaning pitchfork, and ουρανιος (ouranios) meaning heavenly or sky blue, in reference to the forked blue tail. The ending of the new genus name forges a link with the genus Thalurania, in which it was previously included. The genus is feminine.

  • Acknowledgements

    We thank the Cornell Lab of Ornithology for permitting the use of paintings of hummingbirds from the Handbook of the birds of the world. Two referees provided constructive comments on the submitted version of the manuscript.



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    © 2023 The Authors;
    George Sangster, Jimmy Gaudin, and Karl-L. Schuchmann "A new genus for Thalurania ridgwayi (Trochilidae)," Bulletin of the British Ornithologists’ Club 143(1), 63-65, (6 March 2023).
    Received: 22 June 2022; Published: 6 March 2023
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