Proposal (686) to South American Classification Committee

 

Treat Elaenia brachyptera as a separate species from Elaenia chiriquensis

 

Background:   The widespread species Elaenia chiriquensis has three recognized subspecies, nominate chiriquensis found in southern Central America, albivertex widespread in lowlands east of the Andes south to northern Argentina, and brachyptera found in montane forests in southern Colombia and northern Ecuador (Dickinson & Christidis 2014).

 

         Ridgely and Greenfield (2001) based on Coopmans indicated that the voice of brachyptera is very different from chiriquensis and albivertex elsewhere, and suggest that it might represent a distinct species.

 

New information:  Rheindt et al. (2015) analyzed voice and a molecular dataset including mitochondrial NADH dehydrogenase (ND2) and nuclear B-fibrinogen intron 5 to examine the relationships of the three subspecies included within Elaenia chiriquensis using E. mesoleuca (identified as sister to chiriquensis in a previous study (Rheindt et al 2008).  The molecular dataset shows the lowland chiriquensis and albivertex to be only weakly differentiated (0.8 to 1.2% different at ND2), whereas brachyptera was more strongly differentiated (3.7 to 4.3%).

 

         Analysis of vocal data found the vocalizations of chiriquensis and albivertex to be quite similar across the entire vocal repertoire.  The taxon brachyptera, however, was quite different in dawn song and in other calls.  Unfortunately the authors had only 1 recording of the dawn song of brachyptera for comparison to the other subspecies; however, they stated that other birds heard at the same time were very similar.  All three subspecies had a standard pattern of Elaenia dawn song, with a similar phrase (which varies little across the genus) and a more complex phrase.  The dawn song of brachyptera differs from those of the other two subspecies in the number of elements (having only 2 versus multiple elements) in the complex phrase, the quality and pitch of the first element in the complex phrase, and the quality of the second element.  This makes for a very different looking sonogram (Figures 4 and 5 in Rheindt et al. 2015).

 

         The authors recognized two types of calls, whistled and burred calls, in both chiriquensis and albivertex.  These calls are very similar in these two taxa.  The authors recognized 3 call types in brachyptera: two apparently homologous to the whistled and burred calls of the other taxa, and a third call that they refer to as a rattle that appears to have no equivalent in either chiriquensis or albivertex.  Both the whistled and burred calls in brachyptera are higher pitched, and the call shape on the sonogram is more asymmetric.  The rattle call is very different from anything given by the other taxa (and the authors state that they found nothing similar in the genus).  The sample size for calls was much better than for songs, with recordings from at least 18 different individuals.

 

         Based on both vocalizations and molecular data, Rheindt et al. (2015) have determined that montane populations of the chiriquensis group from the east slope of the Andes in Ecuador are brachyptera, not albivertex as sometimes assumed.

 

         Rheindt et al. did not discuss morphological differences between brachyptera and other chiriquensis at all, stating that the 3 subspecies differ “in the hues of their body coloration” and that brachyptera is slightly smaller, citing Hosner 2004 (HBW).  Although I recognize that plumage differences between different Elaenia are always slight, the lack of any useful morphological information is a shortcoming of this paper.

 

Note: I looked quickly at Field Museum specimens.  We have nothing identified as brachyptera, but we have a series collected at El Tambo in Cauca between 1700 and 2400 m, which is on the Andean slopes on the west side, just north of the known range in NariĖo of brachyptera.  A quick look at these birds makes me wonder if they are brachyptera.  They are dark-chested compared to a series of albivertex from Meta.  The geography described in this paper would also suggest brachyptera, but a question for another day.

 

Recommendation:   I recommend a YES vote to split Elaenia brachyptera from Elaenia chiriquensis as suggested by Rheindt et al. (2015) based on its distinct voice, and supported by its genetic distance from the rest of E. chiriquensis.  I would be happier with some morphological analysis, but it is not likely to be very informative anyway.

 

English names: Rheindt et al. (2015) suggested an English name of Coopmans’s Elaenia for brachyptera in recognition of Paul Coopmans’ role in making people aware of the distinctiveness of this taxon.  Ridgely and Greenfield (2001) suggested NariĖo Elaenia for this species.  However, given its expanded range to the eastern slope of the Andes, NariĖo Elaenia is becoming a progressively less-appropriate name for brachyptera.  I recommend the use of Coopmans’s Elaenia, and further recommend no change to Lesser Elaenia for the widespread Elaenia chiriquensis, now excluding the narrowly distributed brachyptera.

 

References:

Dickinson, E. C. (ed.). 2003. The Howard and Moore complete checklist of the birds of the World, Revised and enlarged 3rd Edition. Christopher Helm, London, 1040 pp.

Hosner, P.A. (2004) Genus Elaenia. In: del Hoyo, J., Elliott, A. & Christie, D.A. (Eds.), pp. 267-274. Handbook of the Birds of the World. Vol. 9. Cotingas to Pipits and Wagtails.  Lynx Edicions, Barcelona.

Rheindt, F. E., L. Christidis, and J. A. Norman.  2008a. Habitat shifts in the evolutionary history of a Neotropical flycatcher lineage from forest and open landscapes. BMC Evolutionary Biology 8: 193 (18 pp.).

Rheindt, F. E., N. Krabbe, A. K. S. Wee, and L. Christidis.  2015.  Cryptic speciation in the Lesser Elaenia Elaenia chiriquensis (Aves: Passeriformes: Tyrannidae).  Zootaxa 4032: 251–263.

Ridgely, R. S., and P. J. Greenfield.  2001. The birds of Ecuador. Vol. I. Status, distribution, and taxonomy. Cornell University Press, Ithaca, New York.

 

Douglas Stotz, October 2015

 

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Comments from Areta:  YES. I agree with Doug in that a more thorough discussion of plumage features would have been desirable, at least to substantiate the cryptic speciation proposition, which might stem from appreciable differences or from luck in assigning a name to an indistinguishable taxon.  Although a single (diagnostic) dawn song of brachyptera was available, other vocalizations also differ between chiriquensis/albivertex and brachyptera.  Spectrograms should have made reference to the localities, dates and sources of recordings to foster our understanding of what is being shown, and more details on the sources of vocalizations from other species in the Appendix would also have been more than welcome, especially given that ID errors are frequent in the genus.  Despite these shortcomings, the essential information to consider both taxa as separate biological species is present in the paper.”

 

Comments from Stiles: “YES, albeit a bit hesitantly. For one thing, albivertex also occurs rather widely on the western slope of the Eastern Andes in Colombia, and in our large series here a number of specimens are notably dark-chested (young birds? plumage wear?).  The difference in measurements given by Meyer de Schauensee indicates considerable overlap between brachyptera and albivertex, also seen in a group of 5 specimens from the Popayán area (including “Munchique-El Tambo”, presumably brachyptera) and albivertex from further north, and we have a recent specimen from Tumaco that I would definitely place with albivertex, thus making “NariĖo Elaenia” less appropriate, so Coopmans’s Elaenia seems a better name.

 

Comments from Jaramillo: “YES – Vocal and molecular data come to the same conclusion, that brachyptera deserves species rank. I think that Coopman’s Elaenia is an appropriate name.

 

Comments from Zimmer: “YES.  The vocal and molecular data sets are congruent. This is a group in which plumage characters are notoriously subtle and evolutionarily conservative, so the lack of analysis by Rheindt et al (2015), although disappointing, was, as Doug notes, unlikely to be particularly informative.  “Coopman’s Elaenia” sounds good as an English name.”

 

Comments from Remsen: “YES. The differences in song are consistent with song differences in many other related tyrannids ranked as species.  This evidence would be sufficient, in my opinion, regardless of degree of genetic differentiation in a few neutral loci that are basically irrelevant to the biology of these taxa unless they are shown to be parapatric.”

 

Comments from Robbins: “YES, to recognizing Elaenia brachyptera as a species despite the shortcomings of the Rheindt et al. (2015) paper as underscored by both Stotz and Areta.”

 

Comments from Pacheco: “YES.  Vocal and molecular data support the separation from E. chiriquensis.”