Proposal (1039) to South American Classification Committee

 

 

Split Camptostoma obsoletum into six species

 

Background:

Camptostoma obsoletum currently comprises 13 subspecies taxa distributed across Central and South America, from Costa Rica to Uruguay. Fragmentary vocal and genetic evidence suggests that it may include multiple biological species (Ridgely and Tudor 1994, Ridgely and Greenfield 2001, Rheindt et al. 2008). However, current taxonomy remains entirely based on subtle variations in plumage and morphology, which are unlikely to reflect true species limits in this group (Fitzpatrick 2004).

 

New Information:

A newly published analysis of geographic vocal variation in the genus Camptostoma, based on 1,113 recordings of vocalizations from 994 individuals across 783 localities, identified six vocally distinct populations within C. obsoletum (Lima and Vaz 2024). These populations exhibit diagnostic differences in multiple different vocalization types, including vocalizations that are typically species-specific in the Tyrannidae. The populations are mostly allopatric but have abutting ranges over large areas, with little evidence of gene flow between them (Lima and Vaz 2024).

 

Assuming that the several diagnostic differences in multiple vocalization types have the potential to generate substantial premating isolation among these vocally distinct populations, and considering the apparent pattern of parapatry without gene flow between several of these populations, Lima and Vaz (2024) proposed splitting C. obsoletum into six biological species, maintaining vocally undifferentiated taxa with potential plumage differences as subspecies pending further study:

 

·      Camptostoma flaviventre Sclater & Salvin, 1865

o   C. f. flaviventre Sclater & Salvin, 1865

o   C. f. majus Griscom, 1932

o   C. f. orphnum Wetmore, 1957

·      Camptostoma caucae Chapman, 1914

·      Camptostoma pusillum (Cabanis & Heine, 1860)

·      Camptostoma sclateri (Berlepsch & Taczanowski, 1884)

o   C. s. sclateri (Berlepsch & Taczanowski, 1884)

o   C. s. maranonicum Carriker, 1933

o   C. s. griseum Carriker, 1933

·      Camptostoma napaeum (Ridgway, 1888)

o   C. n. napaeum (Ridgway, 1888)

o   C. n. olivaceum (Berlepsch, 1889)

·      Camptostoma obsoletum (Temminck, 1824)

o   C. o. obsoletum (Temminck, 1824)

o   C. o. cinerascens (Wied, 1831)

o   C. o. bolivianum Zimmer, 1941

 

Here’s a figure from Lima and Vaz (2024) illustrating the geographic ranges of the proposed species based on the sound recordings examined. For further details about the figure, including information about extralimital taxa, see Lima and Vaz (2024).

 

 

The proposal is subdivided as follows:

 

A. Treat sclateri (including maranonicum and griseum) as a separate species from C. obsoletum

Camptostoma o. sclateri differs diagnostically from all other taxa except maranonicum and griseum in daytime and dawn songs as well as multiple calls (Lima and Vaz 2024). Although field playback experiments suggest weak behavioral discrimination between sclateri and napaeum based on daytime songs (Freeman et al. 2022), no evidence of hybridization exists despite potential parapatry (Lima and Vaz 2024). Other vocalizations may mediate premating isolation, although this remains untested (Lima and Vaz 2024). Alternatively, sclateri and napaeum may form undetected, narrow hybrid zones.

 

B. Treat pusillum as a separate species from C. obsoletum

Camptostoma o. pusillum differs diagnostically from all other taxa multiple vocalizations, including daytime and dawn songs (Lima and Vaz 2024). There is no evidence of gene flow with adjacent populations (caucae and napaeum), despite potential parapatry (Lima and Vaz 2024).

 

C. Treat caucae as a separate species from C. obsoletum

Camptostoma o. caucae differs diagnostically from all other taxa in daytime and dawn songs and multiple calls (Lima and Vaz 2024). No evidence of hybridization exists with the apparently parapatric pusillum and napaeum, suggesting strong premating isolation (Lima and Vaz 2024).

 

D. Treat napaeum (including olivaceum) as a separate species from C. obsoletum

Camptostoma o. napaeum differs diagnostically from all other taxa but olivaceum in multiple vocalizations, including daytime and dawn songs (Lima and Vaz 2024). While differences with parapatric obsoletum are subtle, and some hybridization may occur, phenotypic distinctiveness despite extensive contact (~3,300 km) suggests substantial—albeit incomplete—reproductive isolation (Lima and Vaz 2024).

 

E. Treat flaviventre (including majus and orphnum) as a separate species from C. obsoletum

Camptostoma o. flaviventre, C. o. majus, and C. o. orphnum collectively form a vocally unique population, differing diagnostically from all others in multiple vocalizations (Lima and Vaz 2024). Although this population occurs only in Central America based on the sound recordings examined by Lima and Vaz (2024), I included it here in the proposal because it may plausibly occur in extreme western Colombia near Panama. I defer to the committee to determine whether South American records exist.

 

References:

Fitzpatrick, J. W. (2004). Family Tyrannidae (Tyrant-flycatchers). In Handbook of the Birds of the World (J. del Hoyo, A. Elliott and D. Christie, Editors). Lynx Edicions, pp. 170–462.

Freeman, B. G., J. Rolland, G. A. Montgomery, and D. Schluter (2022). Faster evolution of a premating reproductive barrier is not associated with faster speciation rates in New World passerine birds. Proceedings of the Royal Society B 289:20211514.

Lima, R. D., and R. V. Vaz (2024). Divergence in vocalizations indicates cryptic speciation in Camptostoma tyrannulets. Ornithology: ukae058[RL1] .

Rheindt, F. E., J. A. Norman, and L. Christidis (2008). Genetic differentiation across the Andes in two pan-Neotropical tyrant-flycatcher species. Emu 108:261–268.

Ridgely, R. S., and P. J. Greenfield (2001). The birds of Ecuador: status, distribution, and taxonomy. Cornell University Press.

Ridgely, R. S., and G. Tudor (1994). The birds of South America. Volume 2 (The Suboscine Passerines). University of Texas Press.

 

 

Rafael D. Lima, December 2024

 

 

Note from Remsen on English names: A separate proposal on English names will be needed if any of these proposals passes.

 

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Comments from Lane: “YES. Regardless of whether there is a molecular component to this study, I applaud the authors’ efforts to break down a potential headache of a complex, and I see this study as good enough to act upon here. I agree with their assessments of the taxa, the vocal groupings, and their outlining of daughter species. YES to all proposed splits from C. obsoletum.”

 

Comments from Zimmer: “YES to all splits (see separate subproposals below) as advocated in the Proposal, and as suggested by Lima & Vaz 2024.  I have long grappled to make sense of what I was perceiving as vocal distinctions within the C. obsoletum group across its broad range, and have it mesh with plumage differences and understood distributions of named taxa, but without the kind of geographically broad-based and well-sampled vocal analysis conducted by Lima & Vaz (2024), it has remained a muddled mess in my mind.  Part of the confusion is due to the effects of wear and fading on some of the few plumage characters that can actually allow visual discrimination of taxa in the field, and part of it is due to each population having multiple types of vocalizations in their repertoires (songs, dawn songs, contact calls, agitation/interaction calls, etc), and without a systematic, thorough analysis, you can’t be sure that you are always comparing apples to apples and oranges to oranges.  The absence of a molecular component to this study does not bother me, since I believe vocal differences in these phenotypically conserved groups of suboscines are almost always going to provide the strongest indication of species-limits.

 

“A. Treat sclateri (including maranonicum and griseum) as a separate species from C. obsoletum: YES, also matches my field impressions of vocal distinctions.

 

“B. Treat pusillum as a separate species from C. obsoletum: YES, also matches my field impressions of vocal distinctions.

 

“C. Treat caucae as a separate species from C. obsoletum: YES, based upon vocal distinctions and no evidence of hybridization with parapatric pusillum and napaeum, as detailed in Lima and Vaz 2024.

 

“D. Treat napaeum (including olivaceum) as a separate species from C. obsoletum.  YES. This also matches my field impressions of vocal distinctions.

 

“E. Treat flaviventre (including majus and orphnum) as a separate species from C. obsoletum. YES. This one with particular enthusiasm, based on my own field impressions in Panama/s Costa Rica.  I do not, however, have any evidence for whether South American records of flaviventre exist.”