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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Vote tracking chart: https://www.museum.lsu.edu/~Remsen/SACCPropChart968-1043.htm
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.”
Comments from Areta: “I´ve been amassing recordings of Camptostoma for many years now, which match most of Lima & Vaz´s conclusions. The only point of discontent is at the junction of flaviventre, caucae, and pusillum, which seem vocally very similar in some respects but apparently not in others. I am uncertain on whether the daysong of caucae is really the one chosen by the authors, instead of the slower, more whistled vocalization; likewise, I am unable to hear ANY consistent distinction between dawnsongs of flaviventre (https://macaulaylibrary.org/asset/60355 https://macaulaylibrary.org/asset/57359 https://macaulaylibrary.org/asset/147441041) and caucae (https://xeno-canto.org/307322 https://xeno-canto.org/344295 https://macaulaylibrary.org/asset/100724081). The sample sizes are small, which can be tricky in the highly variable Camptostoma dawn songs. I´ve also found some other issues around flaviventre, pusillum, and caucae: see for example this dawn song of pusillum from Zulia (Venezuela) https://macaulaylibrary.org/asset/69881, and this dawn song attributed to caucae from Antioquia (Colombia) https://macaulaylibrary.org/asset/100724081, both of which share a distinctive inflection in the second and third note and sound remarkably alike, and also add this flaviventre in the mix https://macaulaylibrary.org/asset/25603. This one from the Coastal Cordillera of Venezuela seems also quite similar to songs of flaviventre: https://macaulaylibrary.org/asset/69878. Also, these trills from pusillum (https://macaulaylibrary.org/asset/557328701 https://macaulaylibrary.org/asset/530472281 https://macaulaylibrary.org/asset/34477 https://macaulaylibrary.org/asset/478141441) and these of caucae (https://macaulaylibrary.org/asset/283449281 https://macaulaylibrary.org/asset/272722131 https://macaulaylibrary.org/asset/629232892). These voices of pusillum https://macaulaylibrary.org/asset/597111551 are much like this one from a zone of presumed caucae https://macaulaylibrary.org/asset/534542081 which in turn is very similar to this one of caucae https://macaulaylibrary.org/asset/626683461, and this one of flaviventre https://macaulaylibrary.org/asset/67231361.
“Given the broad similarities, I am not convinced that flaviventre, caucae and pusillum are different species, and so I vote to recognize them under a single species: C. pusillum, or alternatively, split pusillum and leave flaviventre and caucae as one thing (which also seems problematic). The most striking difference in vocalizations seems to be the trill that has been attributed to caucae, and which seems to be missing from other populations. Is this vocalization really from Camptostoma? Has this gone unrecorded in flaviventre? After hearing a fair share of recordings unsystematically, I came away unconvinced of the vocal distinctions, especially those between caucae and flaviventre. Maybe misidentifications to taxon are playing badly on us here, but I can easily imagine the vocal types transitioning through geography (e.g., based on what I hear, some pusillum sound slightly higher-pitched and somewhat faster than caucae and flaviventre, especially if one compares northern to southern examples), and the similarities seem to me to carry more weight than the differences. I don´t think that the spectrogram of the diurnal song of flaviventre is really representative of the taxon: in listening to all the daytime songs assigned to this category by Lima & Vaz, I hear a lot of variation, most of which do not fit the spectrogram. I am not fully convinced of anything of the above, but I also do not see strong evidence to split the three as different species. I would like to hear what others think on the northern South America-southern Central America issue.
“Meanwhile, my votes are:
A. Treat sclateri (including maranonicum and griseum) as a separate species from C. obsoletum --- YES
B. Treat pusillum as a separate species from C. obsoletum --- YES
C. Treat caucae as a separate species from C. obsoletum --- YES (separate from C. obsoletum) and NO (to treat is as a species on its own): treat caucae as subspecies together with C. pusillum or together with flaviventre.
D. Treat napaeum (including olivaceum) as a separate species from C. obsoletum --- YES
E. Treat flaviventre (including majus and orphnum) as a separate species from C. obsoletum --- YES (separate from C. obsoletum) and NO (to treat is as a species on its own): treat flaviventre as subspecies together with C. pusillum or together with caucae.”
Comments from Niels Krabbe (voting for Del-Rio): “After reading Nacho's comments, I am in doubt whether pusillum, caucae, and flaviventre are separate species, but YES to the rest of the suggested splits. So:
“A: YES. Treat sclateri (including maranonicum and griseum) as a separate species from C. obsoletum
B: YES. Treat pusillum as a separate species from C. obsoletum [but including the subspecies flaviventre, caucae, majus, and orphnum]
C: YES and NO. Treat caucae as a separate species from C. obsoletum [but as a subspecies of pusillum]
D: YES. Treat napaeum (including olivaceum) as a separate species from C. obsoletum
E: YES and NO. Treat flaviventre (including majus and orphnum) as a separate species from C. obsoletum [but as a subspecies of pusillum]”
Additional comments from Rafael Lima: “I do not have field experience with the northern taxa, so I cannot confirm with certainty that the rapid trill belongs to Camptostoma. Our assumption was based on two points. First, multiple experienced observers and ornithologists have recorded this vocalization and consistently attributed it to Camptostoma. Second, if the slower, more whistled vocalization in Figure 9H represents the daytime song of caucae, then there is no clear homologous counterpart among similarly structured vocalizations in flaviventre and pusillum (Fig. 9G–I). However, the key point remains: as noted in the paper, regardless of whether the daytime song of caucae is the rapid trill (Fig. 2D) or the slower, more whistled vocalization (Fig. 9H), caucae still has a distinctive daytime song. In other words, the conclusion that caucae has a unique daytime song remains unchanged, irrespective of this analytical choice. (All data and scripts necessary to replicate the analyses and figures are publicly available at https://datadryad.org/dataset/doi:10.5061/dryad.612jm64dm, allowing for alternative analyses to test whether different methodological choices affect the conclusions.)
“Regarding the dawn songs of flaviventre, pusillum, and caucae, they are indeed similar. While small sample sizes for flaviventre and caucae introduce some uncertainty, the subtle differences in their dawn songs were consistently captured in the measurements of the main phrase (Fig. 5), suggesting they are not spurious. However, even if one assumes that these dawn song differences are artifacts of sample size limitations, the distinctiveness of their daytime songs remains.
“Beyond the magnitude of vocal differences, the apparent pattern of widespread parapatry without gene flow between caucae and pusillum further supports their recognition as separate species (as discussed in the paper). The case for treating pusillum as distinct from flaviventre is less strongly supported, as it relies on the (subtle) vocal differences alone. Still, I consider the differences in their daytime songs alone sufficient to justify treating all three taxa as separate species.”