Proposal (698) to South American Classification Committee
Recognize Zimmerius chicomendesi Whitney et al. 2013 as a species
Background: Zimmerius are small-bodied, frugivorous tyrannulets that are widespread in wooded habitats from southern Mexico south to central Bolivia and central Brazil (or to southeastern Brazil, if Phyllomyias griseocapilla Gray-capped Tyrannulet proves to be a Zimmerius, as suggested by Whitney et al. 2013). The plumage of all Zimmerius is drab. The seemingly dull and innocuous outward appearance of these tyrannulets belies the complexities of their phylogenetics. SACC already has grappled with several proposals dealing with this genus, some of which passed and some of which did not. For a review, see , on lumping Zimmerius chrysops and Z. viridiflavus; , on splitting Zimmerius gracilipes; , on splitting Zimmerius chrysops; , on splitting Zimmerius vilissimus; and Rheindt et al. (2008) and (2013).
Most taxa of Zimmerius were described in the 19th or early 20th century. It was something of a surprise, then, when Jose "Pepe" Alvarez discovered a new species of Zimmerius, Z. villarejoi Mishana Tyrannulet, in 1997 (Alvarez Alonso and Whitney 2001). The type locality of villarejoi is very close to the major Amazonian port of Iquitos, in northern Peru. As Alvarez and Whitney pointed out, even then there was evidence of yet another previously unknown Zimmerius, in the Rio Mayo Valley in the foothills of the Andes in San Martin, Peru, southwest of the type locality of villarejoi. The first specimen of the Mayo Valley population had been collected in 1912 (!), and seemed to be identical to villarejoi from near Iquitos; but at the time of Alvarez and Whitney (2001), the Mayo Valley population was unknown in life. Subsequently the Mayo Valley population has been collected again, by Dan Lane and colleagues (LSU), and its vocalizations documented (see , and Whitney et al. 2013).
New information: The latest twist is the discovery, in 2009, of yet another unknown Zimmerius, this time in central Amazonian Brazil. This population currently is known from the east bank of the Rio Madeira east to the Aripuana/Roosevelt/Maderinha drainage. This population was described by Whitney et al. (2013) as a new species, Zimmerius chicomendesi Chico's Tyrannulet.
In plumage, chicomendesi appears to be indistinguishable from both villarejoi and from the villarejoi look-alike in the Mayo Valley, which Whitney et al. refer to as aff. villarejoi. All three of these populations also inhabit somewhat similar habitats: villarejoi in white sand forests (locally known as varillales), aff. villarejoi in semidry forests in the Mayo Valley, and chicomendesi in campina woodland and scrub.
Other than having a highly disjunct range, chicomendesi differs from villarejoi and aff. villarejoi in two ways: it is slightly smaller than the two other populations (these differences being especially apparent in body mass; see the Supporting Information); and it has slightly different vocalizations, which are described as "notably lower in frequency" than the otherwise similar vocalizations of villarejoi and aff. villarejoi. Their summary is based on a relatively small number of samples (especially of aff. villarejoi; see Supporting Information). Sonograms of vocalizations of all three are presented, but I didn't notice any quantitative comparisons of songs or calls across these taxa.
There are only two proposed new taxa from the 2013 new species special volume for which there is no associated phylogenetic analysis, and this Zimmerius is one of them (the other is Tolmomyias sucunduri, dealt with in , although the full story on Tolmomyias has not yet been told). Alvarez and Whitney (2001) suggested that villarejoi was sister to Zimmerius cinereicapillus Red-billed Tyrannulet. Rheindt et al. (2013) indeed found that cinereicapillus was sister to what they identified as villarejoi, although their samples are from the Mayo Valley and so represent aff. villarejoi sensu Whitney et al. (2013). Presumably villarejoi and chicomendesi, so similar in morphometrics, plumage, and vocalizations, also belong to this clade, but the relationships among them await a more comprehensive phylogenetic analysis. Whitney et al. (2013) further suggested that "other, undiscovered members [of this group] should now be sought in unexplored regions of the Amazon basin".
Recommendation: This case is somewhat similar to that of Nystalus obamai : very low levels of phenotypic differentiation, coupled with small but apparently consistent vocal differences. The other feature here is that chicomendesi is highly disjunct from villarejoi and aff. villarejoi, although Whitney et al. (2013) predicted that geographically intermediate populations may yet be discovered. My recommendation is a weak YES. Note that chicomendesi already is accepted by Dickinson and Christidis (2014), by the , and by the CBRO (Piacentini et al. 2015).
Alvarez Alonso, J., and B.M. Whitney. 2001. A new Zimmerius tyrannulet (Aves: Tyrannidae) from white sand forests of northern Amazonian Peru. Wilson Bulletin 113: 1-9.
Dickinson, E.C., and L. Christidis (editors). 2014. The Howard and Moore complete checklist of the birds of the world. Fourth edition. Volume 2. Passerines. Aves Press , Eastbourne, United Kingdom.
Piacentini, V. de Q., A. Aleixo, C.E. Agne, G.N. Maurício, J.F. Pacheco, G.A. Bravo, G.R.R. Brito, L.N. Naka, F. Olmos, S. Posso, L.F. Silveira, G.S. Betini, E. Carrano, I. Franz, A.C. Lees, L.M. Lima, D. Pioli, F. Schunck, F. Raposo do Amaral, G.A. Bencke, M. Cohn-Haft, L.F.A. Figueiredo, F.C. Straube, and E. Cesari. 2015. Annotated checklist of the birds of Brazil by the Brazilian Ornithological Records Committee / Lista comentada das aves do Brasil pelo Comitê Brasileiro de Registros Ornitológicos. Revista Brasileira de Ornitologia 23: 91-298.
Lista comentada das aves do Brasil pelo Comitê Brasileiro de Registros Ornitológicos. Revista Brasileira de Ornitologia 23: 91-298.
Rheindt, F.E., J.A. Norman, and L. Christidis. 2008. DNA evidence shows vocalizations to be better indicator of taxonomic limits than plumage patterns in Zimmerius tyrant-flycatchers. Molecular Evolution and Phylogenetics 48:150-156.
Rheindt, F.E., A.M. Cuervo, and R.T. Brumfield. 2013. Rampant polyphyly indicates cryptic diversity in a clade of Neotropical flycatchers (Aves: Tyrannidae). Biological Journal of the Linnean Society 108: 889–900.
Whitney, B.M., F. Schunck, M.A. Rego, and L.F. Silveira, 2013. . Pages 286‐291 in J. del Hoyo, A. Elliott, J. Sargatal, and D.A. Christie, editors, Handbook of the birds of the world. Special volume: new species and global index. Lynx Edicions, Barcelona.
Tom Schulenberg, January 2016
Comments from Zimmer: “YES. Although Whitney et al. (2013) did not present a quantitative vocal analysis comparing vocalizations of chicomendesi, villarejoi and what they refer to as aff. villarejoi, the various vocalizations appear (based upon the sonograms presented) to differ qualitatively between taxa beyond the noted differences in frequency. This is true of both songs and the homologous two-note calls. The sonograms of aff. villarejoi sensu Whitney et al (2013) appear more similar to those of chicomendesi songs and calls than they do to the corresponding vocalizations of villarejoi. I would say this is true of the note shapes of the two-note calls, and of the constituent notes making up the songs. Those note-shape similarities are reflected in qualitative similarities (to my ears anyway) between the San Martin villarejoi and chicomendesi, at least based upon the various recordings that I listened to on Xeno-Canto. Nonetheless, I think that the 3 taxa, although indistinguishable in plumage characters, and possessing similar vocal repertoires, are different enough vocally, and with clearly disjunct distributions, as to warrant recognition as separate species. As an aside, I think Whitney et al. (2013) are also correct in their suggestion that Gray-capped Tyrannulet (Phyllomyias griseocapilla) will ultimately prove to be a Zimmerius, an assertion that I’ve been making for years, based upon plumage pattern, vocal repertoire, and foraging behavior and posture.”
Comments from Claramunt: “YES. Morphometric data suggests that chicomendesi is smaller than the San Martín population (aff. villarejoi). Comparison with true villarejoi (from Iquitos) is difficult given the low number of specimens available; the few specimens of villarejoi tend to be intermediate between chicomendesi and the San Martín birds and cause most of the overlap in measurements. This is what you would expect if body size changed gradually E to W, or if foothill birds are larger than lowland birds for some ecogeographic reason. However, vocal data suggest that this is not a case of intraspecific geographic variation. Regarding vocal data, there is no quantitative analysis, but Whitney et al. stated that homologous vocalizations are “immediately and primarily distinguishable”, implying that vocalizations vary in a discrete way, whit no overlap or intermediates. One aspect that caught my attention is the significant lower frequency of chicomendesi vocalizations, against the expectation for a smaller bird. This aspect suggests to me that this is not a case of intraspecific variation and something else is going on, at least regarding allometry between body size and vocal tracts that suggests a history of independent evolution and accumulation of phenotypic differences. Therefore, the Brazilian birds do not seem to be just a new population of villarejoi and I tentatively concur with Whitney et al. and Tom in that they deserve species status.”
Comments from Remsen: “YES. I am persuaded by the points made by Tom, Kevin, and Santiago.”
Comments from Stiles: “YES. I too find the arguments of Tom, Kevin and Santiago persuasive.”
Comments from Areta: “YES. The diagnostic calls and songs of all three species in the complex support their recognition as different species. I had to dig into sound archives (MLNS and XC) to convince myself that differences in shape and pitch in calls and song notes were consistent within each taxon. Despite some variation, the spectrograms shown by Whitney et al. (2013) constitute good representations of the vocal differences between these morphologically very similar taxa. I wonder whether other to-be-found populations will sound intermediate between any of the currently recognized vocally diagnosable units, especially given the vocal similarities between aff. villarejoi and chicomendesi.”
Comments from Pacheco: “YES. I also agree that the data presented so far are sufficient to agree with Tom's proposal. Even though the population of San Martín (aff. villarejoi) proves in the future be an isolated population of the same type as the newly discovered Brazilian Amazonian scrub, the name must be chicomendesi.”
Comments from Jaramillo: “YES – I am particularly persuaded by the comments by committee members with more experience with this group, as well as their independent listen and analysis of voice. Thanks for that help!”
Comments from Robbins: “YES, based on comments by Tom et al. for recognizing Zimmerius chicomendesi as a species.”