Scytalopus opacus androstictus, Krabbe, Niels & Cadena, Carlos Daniel, 2010

Krabbe, Niels & Cadena, Carlos Daniel, 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, pp. 56-66 : 63-65

Scytalopus opacus androstictus ssp. nov. Krabbe & Cadena

HOLOTYPE: An adult male, deposited in the Zoological Museum, University of Copenhagen ( ZMUC 80126). Collected by N. Krabbe (collector’s number NK12- 9.11.92) on 9 November 1992 along the Jimbura-Zumba road in Cordillera de Las Lagunillas, Loja Province, Ecuador (4°43'S, 79°26'W; 3450 m). Tissue sample in ZMUC (number 125728). A recording of the song of this individual was deposited on XenoCanto (number 35112).

Diagnosis. Similar in measurements and plumage coloration to S. opacus opacus from northern Ecuador and central Colombia, but differs vocally by its song-like call, and genetically. Additionally, in seven of nine adult males (and three more observed in the field) most or all of the greater primary coverts in both wings are albinistic, a trait not reported in nominate S. opacus .

Description of holotype. Capitalized color names and numbers from Smithe (1975): Above Blackish Neutral Gray (82), wings and tail very faintly washed with Brussels Brown (121B), rump and tips of tertials with faint, 1 mm wide bars of this color and blackish. Greater primary coverts white. Underparts including underwing uniform, between Dark Neutral Gray (83) and Medium Neutral Gray (84), tips of feathers of lower flanks and under tail coverts with 1 mm wide blackish and Tawny Olive (223D) bars. Weight 16.8 g. Wing chord 53 mm, wing flat 56 mm, tail length 39 mm, tarsus length 22.3 mm. Bill from fore edge of operculum 5.4 mm, from skull 10.3 mm, from mandible fork 6.4 mm. Tail composed of ten rectrices. Irides dark brown, maxilla blackish, mandible blackish brown, feet (tarsi and toes) fuscous. Testes medium enlarged (5 x 2.5 mm), seminal vesicle enlarged. Stomach contents: remains of small insects.

Variation among males. The nine adult males examined are remarkably uniform. Seven individuals vary slightly in the coloration of the primary coverts, which range from being mostly to entirely white; three additional individuals observed in the field possessed this spot, but two adult male specimens from southernmost Zamora-Chinchipe (ZMUC 80128, LSUMZ 83373) show no white and thus do not differ from nominate S. opacus morphologically.

FEMALE: Two adult and two subadult females appear indistinguishable from corresponding plumages of nominate S. opacus .

Description of juvenile. A recently fledged male (ZMUC 80131) with tail still in pin and crown feathers tipped with long down is Prout's Brown (121A) above, lightly barred blackish and with narrow buff tips on the secondaries. The throat and breast are Pale Pinkish Buff (121D) lightly mottled with blackish, belly dirty white and unbarred, sides, flanks and vent dirty white grading to Mikado Brown (121C) on sides of lower breast, and barred blackish. The upperparts are slightly darker brown and the belly paler than in four specimens of nominate S. opacus , but this difference might not be constant, considering the broad range of plumage variation seen in juveniles of nominate S. o. opacus , even within a locality ( Krabbe & Schulenberg 1997).

Distribution and habitat. S. o. androstictus inhabits the East Andes south of the Río Zamora in southern Ecuador, and the Andes of northernmost Peru north of the Río Marañón, on the eastern flank of the Huancabamba valley. It occurs in treeline scrub at elevations ranging from 3000 to 3650 m, locally down to 2600 m along exposed ridges. On the eastern slopes it is replaced below and in taller and more bamboodominated vegetation by S. parkeri Krabbe & Schulenberg and also meets the (as yet unnamed) eastern form of S. latrans Hellmayr , which locally ascends the slopes through disturbed humid forest. On the western slopes it is replaced below in drier, more open scrub by S. latrans subcinereus Zimmer.

Vocalizations. The distinctive calls of S. o. androstictus are described above and shown in Fig. 3 . In spite of this taxon’s long genetic isolation and markedly different call, its song does not differ appreciably from that of S. o. opacus ( Table 3; Figs. 1–2 ), except by lacking the 1–3 churring introductory notes found in 16 of 21 recordings of opacus ( Fig. 5 ) and by sometimes being delivered without pause for two minutes or more, much longer than any recorded song of S. o. opacus . Usually, however, the song is 4–12 s long, as in nominate S. opacus . When S. o. androstictus in rare cases gives an introductory note, i.e. pauses after the first note, the note is of the same pitch and quality as the following notes. In vocalizations of both forms of S. opacus as well as in S. canus , the second, occasionally the first harmonic is loudest, and several more harmonics are often audible.

Etymology. The name refers to the white spot on the primary coverts found in most males, setting it apart from a nearby (Cordillera Colán, Amazonas, Peru) population, vocally unknown but presently referred to S. parvirostris Zimmer , in which a similar spot is found but in females only ( Krabbe & Schulenberg 1997).

Conservation. Our revised classification of the Scytalopus canus complex has implications for conservation because a taxon that was formerly considered to represent a single species actually consists of three differentiated lineages. However, although they range over fairly small areas, there seems to be no immediate threat to the survival of any of them. The entire Ecuadorian part of the range of S. opacus androstictus lies within two large and continuous protected areas: Podocarpus National Park and Bosque Protector Colambo-Yacuri. Much of the range of S. o. opacus also lies within large national parks in Ecuador (e.g. Sangay, Llanganates, Cayambe-Coca) and Colombia (e.g. Los Nevados, Puracé). In the Western Andes of Colombia, S. canus is so far known to occur on Páramo de Paramillo, which is declared a national park, and Páramo de Frontino, of which only a small part is protected. It would be of interest to determine if it occurs on other paramos in the Western Andes, several of which are protected. The first one south of Frontino is entirely encompassed by a nature reserve, Farallones de Citará. It is separated from Frontino by a pass of 2200 m, higher than the lowest pass between Frontino and Paramillo (2150 m), so S. canus presumably also occurs here. Further south, the paramos are separated by passes lower than 1800 m. It would be of conservational interest to determine to what degree the range of S. canus coincides with that of Coeligena orina Wetmore , another bird confined to humid treeline scrub in the Western Andes and so far only recorded from Farallones de Citará and Frontino (Krabbe et al. 2005).

Biogeography. It remains to be determined if S. canus evolved in situ or arrived to the northern end of Western Andes from the south, or through dispersal from the Central Andes across the Cauca Valley (see discussion in Krabbe et al. 2006). If it came from the south, it seems likely that all the highest paramos in this cordillera hold populations.

The restricted range of S. o. androstictus in the Andes in northernmost Peru and southernmost Ecuador closely matches that of Metallura odomae Graves , which is also replaced by a close relative ( M. williami atrigularis Salvin ) north of the Río Zamora. Three other forms, Grallaria ridgelyi Krabbe et al. , Thryothorus euophrys atriceps (Chapman) , and a yet undescribed subspecies of Synallaxis unirufa Lafresnaye (J. V. Remsen & NK, unpubl.data) appear to have similar ranges, except that they also occur in forest down to ca. 2200 m and might range into the southern Cordillera del Cóndor (known to be the case for Grallaria ridgelyi ; T. Mark, unpubl. data). The role of the ca. 10 km wide, dry Río Zamora valley as a dispersal barrier for treeline birds was first recognized by Robbins et al. (1994) and further discussed by Krabbe (2008). Three species, Grallaricula lineifrons (Chapman) , Anairetes agilis (Sclater) and Urothraupis stolzmanni Taczanowski & Berlepsch , all confined to humid treeline scrub, have never been reported south of the Río Zamora despite presence of seemingly suitable habitat to the south. In contrast, some species occupying this habitat range across both sides of the Río Zamora (e.g. Buthraupis wetmorei R.T. Moore and eximia Boissonneau, evidence that different species respond differently to landscape features and historical events in the Andes.

Figures

FIGURE 1. Half second sequences of songs of (A) Scytalopus c. canus from Frontino, Antioquia, Colombia, (B) northern S. c. opacus from Azuay, Ecuador, and (C) southern S. c. opacus from Zamora-Chinchipe, Ecuador. Notice the churring, higher pitched and much slower paced notes of S. c. canus. Differences in note quality between northern and southern S. c. opacus are not constant.

FIGURE 2. Complete songs of (A) Scytalopus c. canus from Frontino, Antioquia, Colombia, (B) northern S. c. opacus from Azuay, Ecuador, and (C) southern S. c. opacus from Zamora-Chinchipe, Ecuador. Notice that in S. c. canus the pitch falls rapidly in the beginning of the song. As in the example shown, most songs of northern S. c. opacus have one to three introductory notes. The song length of all three ranges from 4 to 12 s.

FIGURE 3. Calls of (A – B) Scytalopus canus canus from Frontino, Antioquia, Colombia, (C – D) northern S. c. opacus from Tungurahua and Carchi, Ecuador, and southern S. c. opacus from (E) Piura, Peru and (F – G) Zamora-Chinchipe, Ecuador.

FIGURE 5. Beginning of song of northern S. c. opacus from Azuay, Ecuador, including two introductory notes. In southern S. c. opacus there is usually no introductory note and if present, it is of the same pitch and quality as the following notes.