Proposal (775) to South American Classification Committee

Split Urochroa bougueri into two species

The genus Urochroa has been considered monotypic by virtually all authors in the past, despite the fact that notable differences exist between the two subspecies of bougueri: nominate bougueri and leucura. Ridgely & Greenfield (2001) were the first to suggest that two species might be involved, although they did not implement this suggestion, which was formally taken up by del Hoyo & Collar (2014) and endorsed by Donegan et al. (2015). Here I consider this question in more detail. The previous authors based their decision mainly upon details of plumage coloration and distribution, although Donegan et al. did find appreciable differences between the call notes of the two -the songs of these taxa (if indeed they do sing) have yet to be recorded. Urochroa. b. bougueri is restricted to the very wet Pacific slope of the Western Andes from Colombia to W Ecuador, typical of Chocó endemics, whereas leucura occupies the Eastern slope of the Andes from southern Colombia south to central Ecuador; both occupy middle elevations between ca. 1000 and 2000 m. Here I examine this question in rather more detail.

The plumage characters used by previous authors to justify this split are summarized in the following table (with some amendments I have added).

Character	Sex	bougueri	leucura
Upperparts	♂	Very dark: blackish greenish-bronze, brighter bronze on upper tail-coverts	Much paler and brighter green throughout, including upper tail-coverts
Central rectrices	“	Black, more or less tinged bluish green	Greenish bronze, in some with bluish tinge distally
Lateral rectrices	“	R2-4 extensively white, especially on inner webs; outer webs with black borders and along shafts; outer web r5 mostly black, white only at base: inner web also with broad black border	R2-4 almost entirely white with at most narrow black borders toward tip; r5 similar but black border of outer web longer and somewhat broader.
Sides of head	“	Blackish, but with a conspicuous short, broad rufous malar stripe extending back from gape; a small but definite cinnamon postocular spot	Greenish-black, the rufous malar marking absent or limited to an inconspicuous small, dark spot at gape; cinnamon postocular spot usually lacking, at most very small and inconspicuous.
Throat to upper breast	“	Dark violet-blue, sharply defined posteriorly	Similar or slightly paler, brighter blue, may be less sharply defined
Lower breast	“	Usually some dark greenish-bronze feathers, especially laterally	Bright green feathers more extensive laterally, but may form a continuous band across breast
Abdomen	“	Dark brownish-gray with some dark greenish-bronze feathers on sides and flanks	Decidedly paler gray, with more extensive green on sides and flanks
Throat and chest	♀	Similar to male but somewhat less extensive posteriorly, the blue feathers with dark grayish-brown fringes giving a scaly appearance	Also similar to male but the blue slightly paler and brighter; at most very narrow pale gray fringes broader posteriorly, giving way to a green-spotted effect on extreme lower breast
Abdomen	“	Similar to that of male	Similar to or slightly paler than male

Again, previous authors have failed to mention that bougueri is most conspicuously the darker bird, especially on the upperparts and abdomen, again obvious from several meters away. Also previously overlooked is the fact that bougueri is a much larger bird, sex for sex: see the following table. Overlap in bill, wing, and tail lengths is limited in males, and nonexistent in females, as well as in other parameters in males, but small sample sizes preclude meaningful statistical analyses. In particular, note the much lower body mass, narrower wings and lower wing loading in both sexes of leucura, all of which suggest differences in foraging and aggressive behavior between the two taxa.

Measurement	bougueri ♂♂ (n=7)	leucura ♂♂ (n=2, except where *, n=1)	bougueri ♀♀ (n=3)	leucura ♀♀ (n=2)
Total culmen	34.36 ±1.50	32.80 ± 1.13	36.27 ± 1.29	33.25 ± 0.21
Closed wing length	78.63 ± 2.43	76.70 ± 0.57	73.97 ± 0.85	71.20 ± 1.27
Tail length	47.76 ± 2.81	45.87 ± 1.16	45.25 ± 0.35	43.05 ± 0.49
Tarsus length	7,57 ± 0.35	6.75 ± 0.07	7.13 ± 0.22	6.65 ± 0.07
Body mass	11.71 ± 0.60	8.90 ± 0.57	10.30 ± 0.53	7.75 ± 0.21
Wing shape	2.973 ± 0.054	0.311*	2.836 ± 0.081	3.036 ± 0.042
Wing loading	0.304 ± 0.020	0.275*	0.238 ± 0.010	0.245 ± 0.030

Specimen photos:

With regard to possible species status, the two most important differences in color between the two, the present vs. absent rufous malar and the more striking differences in tail colors, could well be important in species recognition and mate choice. The large size difference is unusual among undoubted subspecies; an example of two species differing less in plumage but similarly in size are the narrowly parapatric Campylopterus excellens and curvipennis of southwestern Mexico. The differences in color at least match some of those in the closely related genera Heliodoxa and Boissoneaua but size differences, both between species and between sexes of the same species, are less extreme than in the two taxa treated here; the same goes for the also related genus Coeligena. It is perhaps worth mentioning that on the same slope as leucura, two species of Eutoxeres differing slightly less in plumage but virtually identical in size overlap rather broadly without interbreeding. Vocal differences, as evidenced by several sonograms, also exist, based on the available evidence– but both forms are notably quiet and perhaps do not sing at all.

Although genetic evidence is lacking, all of the aforementioned considerations lead me to recommend a YES on this split also. The English epithets “Rufous-gaped” and “White-tailed” Hillstars suggested by Donegan et al. for bougueri and leucura respectively are descriptive and accurate. However, restricting the latter name to leucura rather than to the nominate goes against current practice. Although I prefer these names, if one must bow to convention the more aseptic names Western (or Pacific or Chocó) and Eastern could serve, as the two taxa also show widely disjunct distributions.

F. Gary Stiles

References

Del Hoyo, J. & N.J. Collar. 2014. Illustrated checklist of Birds of the world, vol. 1 (non-Passerines). Lynx Edicions, Barcelona, Spain and BirdLife International, Cambridge, UK.

Donegan, T., A. Quevedo, J.C. Verhelst, O. Cortés-Herrera, T. Ellery & P. Salaman. 2015. Revision of the status of Bird species occurring in Colombia, with discussion of BirdLife International’s new taxonomy. Conservación Colombiana 23:3-48.

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Comments from Jaramillo: “YES. I find the argument convincing, plumage differences, call differences and size differences to be beyond the level that would be expected in subspecies.”

Comments from Robbins: “YES, for elevating Ieucura to species status based on Gary’s detailed analyses of the morphology.”

Comments from Pacheco: “YES. The information presented seems to me sufficient to corroborate the proposal.”

Comments from Areta: “YES. I would like to see more thorough comparative studies on plumage variation and vocalizations, but published evidence tips the balance towards recognition of two species.”

Comments from Remsen: ”YES. Using a comparative approach within hummingbirds in terms of degree of phenotypic differentiation indicates that Gary’s tabulation of differences strongly favors species rank, and Donegan et al.’s call note differences, although slim on sample size, are consistent with that treatment. Assigning taxon rank to allotaxa is always problematic, but in my opinion of available evidence suggests burden-of-proof would be on continued treatment as conspecific. I continue to point out that DNA sequence data for neutral loci in these allotaxa provide little if any relevant information for a taxonomic decision – we already know they differ, assuming that the suite of phenotypic differences is genetically based; therefore, unless genetic distance was at one of the far extremes, how would this metric be useful? What if there were NO differences evident in sequence data of neutral loci? All that would say, in my opinion, is that rates of phenotypic characters has been extremely rapid relative to that at neutral loci; the former are potentially directly relevant to whether these populations have crossed the threshold of “no return” in terms of separate evolutionary trajectories, whereas the relevance of the neutral loci to this is uncertain at best.”

“We will need a separate proposal on English names. Cory (1918) used “Pied-tailed Hillstar” for bougueri and “White-tailed Hillstar” for leucura. Use of White-tailed for the daughter species, as advocated by Donegan and favored by Gary, is inadvisable for the reasons mentioned by Gary. In fact, in this case it is unusually bad because U. bougueri sensu lato has always been known as “White-tailed Hillstar” and using “White-tailed Hillstar” for the split species leucura would create obvious problems, despite the match of English and scientific name. In addition, both have “white tails” as evidenced for the use of that name for U. bougueri sensu. I would rank this as by far the worst decision we’ve ever made on English names.”