Proposal (875) to South American Classification Committee

Elevate Penelope bridgesi to species status and endorse an English name

Effect on SACC List: A positive vote would add Penelope bridgesi to the SACC list.

Background. The only SACC note on either taxon, bridgesi or bronzina, which represent the only recognized subspecies of Dusky-legged Guan P. obscura, is as follows:

14a. Evangelista-Vargas & Silveira (2018) treated the subspecies bridgesi of Bolivia and Argentina as a separate species but based on PSC rationale.

Penelope bridgesi was described as a full species by Gray (1860) with the type locality of “Bolivia”, collected by Thomas C. Bridges; holotype in the British Museum (NHM 1846.9.9.42). It was subsequently lumped with P. obscura by Ogilvie-Grant (1893) upon his specimen examination involving seven specimens of obscura and the bridgesi holotype. This arrangement has remained the status quo ever since, although often questioned e.g. Hartert & Venturi 1909, who described bridgesi as being “bien distincte”, besides many other ornithologists describing numerous plumage distinctions and the fact that bridgesi is notably larger than obscura (Delacour & Amadon 2004). Note also that bridgesi lives primarily in Yungas forest and ranges exclusively from southern Bolivia through north-west Argentina.

In contrast bronzina was described as a subspecies of P. obscura by Hellmayr (1914) from Colônia Hansa, Santa Catarina, Brazil, and the two taxa are parapatric in south-east South America and possibly grade into one another. The status of bronzina as a subspecies has largely gone unquestioned except that some authors suggest a merger with obscura (see New Information).

Penelope obscura (together with bronzina) is allopatric by ca.1600 km from bridgesi, and the two live in very different forest types; obscura in gallery forest from the Parana Delta northwards and bronzina also in gallery forest as well as patches of Araucaria forest, in strong contrast to bridgesi, which lives in subtropical Yungas forest in the Andean foothills. The notion that bridgesi also lives in the chaco (Evangelista-Vargas & Silveira 2018) is in error and refers to the foothill intergrade between sierran chaco and Yungas forest, yet this habitat has nothing to do with the dry or humid chaco ecotone.

It seems extraordinary that two so-very-different looking species have been lumped for well over a century with so little discord.

New Information. A study of 104 specimens of bridgesi, obscura and bronzina (Evangelista-Vargas & Silveira 2018) confirmed what was already known on their strong allopatry, and biometric tests revealed no overlap in wing measurements between obscura (including bronzina) and bridgesi, with bridgesi being longer.

Their plumage analysis noted that “all specimens attributed to P. o. bridgesi lacked olive brown coloration with a green tinge to the upperparts (unlike P. o. obscura and P. o. bronzina). Instead, specimens of P. o. bridgesi showed chestnut upperparts contrasting with the black head. The underparts were consistently uniform and slightly paler than the back, whereas in P. o. obscura and P. o. bronzina the coloration of the upperparts was highly variable. The wing coverts of P. o. bridgesi show broad white margins, a character state not found in P. o. obscura and P. o. bronzina, which have indistinct white margins to the wing coverts.” Such statements reiterate the type description that bridgesi has different contour plumage coloration, a very different distribution and intensity (width) of white streaking on different parts of its body; in particular the wing-coverts and breast. This can be clearly seen in these pictures of bridgesi (https://macaulaylibrary.org/asset/31599331, https://macaulaylibrary.org/asset/199545731), and obscura/bronzina (https://macaulaylibrary.org/asset/133418341,https://macaulaylibrary.org/asset/139191981), and is also appreciable in specimens as shown in Figure 5 of Evangelista-Vargas & Silveira (2018).

Evangelista-Vargas & Silveira (2018) also provided re-descriptions of obscura and bridgesi as follows:

Penelope obscura Temminck, 1815

“Re-description. No sexual dimorphism found in plumage coloration. Whitish edges extension of head feathers varies from wide to almost imperceptible. Some individuals show a moderately distinct superciliary stripe formed by short feathers with white edges. Overall color of crown feathers variable, ranging from black, gray to brown. White hue of the edge of the feathers varies individually. Brown back may show greenish, brownish or blackish tinge. Neck, breast, upper back, and shoulders conspicuously edged with white. Birds in the northern parts of the species’ range tend to have more noticeable white streaks on the back, but streaks also may be lacking. The coloration of the underparts is variable and may show a contrastingly darker chest than belly, but underparts may also be uniform dark or lighter than the breast. The belly feathers have contrasting horizontal scaling, which may range from brown to orangish, and may vary in intensity. Tail feathers are dark brown with bronze or purplish sheen. Bare skin of face slaty, legs dusky gray to blackish, and wattle red.”

Penelope bridgesi Gray, 1860

“Re-description. No sexual dimorphism found in plumage coloration. General coloration chestnut, with limited individual variation. Crest feathers dark with whitish margins, most strongly marked on the forehead; little or no trace of an superciliary stripe. Upperparts chestnut, contrasting with the black head and hindneck. Lower parts uniform dull reddish brown and slightly paler than the back. The belly feathers have contrasting horizontal scaling, which may range from brown to orangish and may vary in intensity. Feathers of the neck, mantle and chest are margined with white, wider on the mantle and wing coverts. Tail feathers dark brown with brownish sheen. Bare skin of face slaty, legs dusky gray to blackish, and wattle red.

Furthermore, Pearman (in del Hoyo and Motis (2004)) called attention to vocal distinctions: “The excited calls or alarms of bridgesi (Salta Prov.) are low-pitched whistles mixed with guttural rasps, e.g., “SWig SWI-u, SWig-u KREG, swig-u, u, KREG KREG KREG” etc.; the loud, guttural “KREG” notes are given with more regularity when alarmed, cf. (op. cit.), the calls or alarm of the nominate race [i.e. obscura] (NE Buenos Aires Prov.) are higher pitched, disyllabic and lack the guttural notes of bridgesi, sounding more like: “Wikik Wikik-u, Wikik-u-u, Wikik, Wikik-u” etc.

Discussion

In our own extensive personal experience of obscura and bridgesi, it seems incredulous that they are still regarded as a single species, on the basis of a single unscrupulous museum comparison more than a century ago. We also concur with others that bridgesi is a very much larger guan than obscura as borne out by total length measurements taken at the time of collection (MACN and IADIZA specimen data):

obscura: 480-660 (n=2)

bridgesi: 770-890 (n=9)

Recommendation. We recommend a YES vote to elevate P. bridgesi to species status.

English name. Thus far, only the name Bridges’s Guan has been suggested as an English name (Evangelista-Vargas & Silveira 2018) in reference to the collector of the holotype. Please note the implications of pronunciation since Bridges is a plural surname. As an alternative we promote the name Yungas Guan because bridgesi is the abundant species of guan within its range in Yungas forest. The only other guan species in range is the very localized Red-faced Guan P. dabbenei, which occurs at higher elevations in the alder treeline zone. As such, the common guan species of the Yungas forest is most certainly bridgesi.

We recommend a YES vote to endorse the name Yungas Guan. A NO vote would endorse Bridges’/Bridges’s Guan.

References

Delacour, J. & Amadon, D. (2004) Curassows and Related Birds. Lynx Edicions, Barcelona/The National Museum of Natural History, New York.

del Hoyo, J. & Motis, A. (2004) Update Chapter. Pp. 322-476 in: Delacour, J & Amadon, J. 2004 Curassows and Related Birds. Second Edition. Lynx Edicions and NMNH, Barcelona & New York.

Evangelista-Vargas & Silveira, L. F. (2018) Morphological evidence for the taxonomic status of the Bridges’s Guan, Penelope bridgesi, with comments on the validity of P. obscura bronzina (Aves: Cracidae). Zoologia 35: e12993.

Gray, G.R. (1860) Synopsis of the species of the genus Penelope. Proc. Zool. Soc. London 28: 269-272.

Hartert E. & Venturi S. (1909) Notes sur les oiseaux de la république Argentine. In: Rothschild W, Hartert E, Jordan K (Eds) Novitates Zoologicae XVI. Zoological Museum of Tring, London and Aylesbury, 159–267.

Hellmayr 1914 Critical Notes on the types of little-known species of Neotropical birds. Part 3. Novit. Zool. 21: 158-179.

Ogilvie-Grant W.R. (1893) Catalogue of the Birds in the British Museum 22. Order of the Trustees, London.

M. Pearman and J. I. Areta, August 2020

Note from Remsen on voting: Let’s treat this as two separate subproposals, with “A” being species limits and “B” being English name if A passes.

Comments from Remsen:

“A. YES. On the one hand, size and plumage in general are not characters that are sufficient to define species. Disjunct distribution is also not a sufficient criterion for species range; the degree of “disjunctness” varies on a continuous scale that has no defensible threshold for species rank. In fact, the size differences would be predicted within populations of the same species on the basis of Bergmannian patterns: the higher elevation taxon would be predicted to be larger, as is the case here. Also, habitat differences per se are essentially useless as sufficient criteria for species limits given the notorious flexibility of habitat preferences within many monotypic species. The vocal differences are potentially sufficient criteria on their own, but I would be cautious in using them without a formal study of the range of variation in each species, with N etc. Nonetheless, I vote in favor of the split. Although I would have to check specimens to be sure, it seems clear from the descriptions that the plumage differences between these two are greater than between some taxa ranked as species in Penelope (e.g., P. argyrotis and P. barbata), in which the degree of interspecific plumage variation in general is unimpressive. As pointed out in the proposal, their maintenance as conspecifics seems largely a case of historical momentum with virtually no critical analysis. Delacour & Amadon of course mention the differences between the taxa but made no remarks on whether they might be separate species; however, both authors were notorious lumpers. At this point, the proposal and the Evangelista-Vargas & Silveira paper has me convinced that the burden-of-proof falls on conspecificity. In fact, whether they are sister taxa should also be investigated genetically; I assume from Evangelista-Vargas & Silveira that no phylogeny has included samples from both taxa.

“B. YES on Yungas Guan. In addition to the great differences in range size, I also consider it unresolved as to whether they are sister taxa, so I have even less concern than usual for the “parent-daughter” guidelines of English names.”

Comments from Stiles: “YES to A: morphology, vocalizations, ecology and distribution justify the recognition of bridgesi as a species; YES to B: Yungas Guan is short and appropriate.”

Comments from Claramunt: “YES. In the context of the very conservative Penelope, those few differences are remarkable.”

Comments from Robbins: “ A) YES, to recognizing bridgesi as a species given that plumage morphology differentiation is greater between it and obscura than in other presumed Penelope sister taxa that are recognized as species. The vocal differences described by Pearman are also suggestive for species recognition.

Comments from Zimmer: “(A) YES. With a nod to each of the caveats mentioned by Van, I still think the plumage differences between bridgesi and obscura/bronzina meet the “yardstick” provided between other species pairs with Penelope, particularly when combined with the described vocal and morphometric differences, habitat specialization, and range disjunction. (B) YES to “Yungas Guan” for bridgesi, and retain “Dusky-legged Guan” for obscura + bronzina.”

Comments from Bonaccorso: “ A – YES. Given the evidence gathered, this is repairing a historical mistake, and this is not an exaggeration.”

Comments from Jaramillo: “A. YES – These birds are quite different for Penelope, the size difference alone is perhaps an impediment to interbreeding would they ever meet in life. B. YES – Yungas Guan is the better name.”