Proposal (446) to South American Classification Committee
Treat Scytalopus opacus as a separate species from Scytalopus canus
Species Limits in the Paramo Tapaculo (Scytalopus canus)
The Paramo Tapaculo (Scytalopus canus) is a common bird inhabiting treeline scrub in the Northern Andes that ranges widely in the Cordillera Central of the Colombian Andes and along the Ecuadorean Andes into northern Peru, with additional populations in the Cordillera Occidental of Colombia. The latter populations correspond to the nominate subspecies of S. canus, which was vocally unknown when a comprehensive revision of species limits in tapaculos was conducted (Krabbe and Schulenberg 1997). Therefore, such revision treated S. c. canus and S. c. opacus (from the Cordillera Central, Ecuador and Peru) as conspecific pending additional information.
Recent fieldwork in the Paramo de Frontino area (Antioquia, Colombia) resulted in the first recordings of S. canus canus and in the collection of a specimen with tissue samples for genetic analyses. Songs, calls, and mtDNA sequences of S. canus canus have now been analyzed and compared to those of S. c. opacus from several localities (Krabbe and Cadena 2010); the paper is available at this website:
The analyses show that the song of S. canus canus is sufficiently distinct from that of S. c. opacus to consider these two forms as separate species in the context of the criteria followed to establish species limits in Scytalopus over recent years. Also, the nominate subspecies of canus and subspecies opacus were shown to be more than 5% divergent in mtDNA (ND2) sequences, which indicates a considerable period of isolation.
Krabbe and Cadena (2010) further showed that the populations of S. c. opacus occurring south of the Río Zamora in Ecuador and Peru have very distinctive calls (but similar songs) in comparison to populations occurring north of this river. Also, most males (10 of 12) from southern populations exhibit a white patch on each wing. Further, phylogenetic analyses suggested that northern and southern opacus might not be each other's closest relatives, with the northern population being more closely related to nominate S. canus (a result supported strongly in some analyses but based on a single gene and on sequences of only a handful of individuals).
In sum, Krabbe and Cadena (2010) recommended splitting the Paramo Tapaculo in two separate species: S. canus from the Cordillera Occidental of Colombia and S. opacus from the Cordillera Central of Colombia, Ecuador, and Peru. They further named the southern Ecuadorian and Peruvian population as a new taxon, which they treated as a subspecies of S. opacus (S. o. androstictus). Although this would seem to result in a paraphyletic S. opacus because S. o. opacus appears to be more closely related to S. canus than to S. o. androstictus, Krabbe and Cadena (2010) proposed this treatment considering (1) that paraphyletic species are not at odds with the biological species concept (and that inferences phylogenetic relationships might change as more genes and individuals are considered) and (2) that calls have not been shown to function as mechanisms of reproductive isolation in these birds, except perhaps for examples in Brazilian taxa (see discussion under SACC proposal 329).
For the reasons we described in the paper and that I have summarized here, I recommend voting YES to treat S. canus (Paramillo Tapaculo) and S. opacus (Paramo Tapaculo) as separate species - see rationale for English names in Krabbe and Cadena (2010).
I realize that the situation involving S. o. androstictus merits some discussion, so perhaps committee members could comment on this as well, and we can decide whether this proposal will suffice to accept the treatment proposed in the paper or if it would be worth having a separate proposal to split androstictus from opacus (I would personally maintain these as conspecific pending more data).
Krabbe, N., and C. D. Cadena, C.D. 2010. A taxonomic revision of the Paramo Tapaculo Scytalopus canus Chapman (Aves: Rhinocryptidae), with description of a new subspecies from Ecuador and Peru. Zootaxa 2354, 56-66.
C. D. Cadena, July 2010
Comments from Stotz: “YES. Given the rampant increase in Scytalopus diversity, this split fits in well with what we know about the genus. The situation with androstictus is definitely suggestive but like Daniel I’d like to see more data, and certainly a separate proposal.”