Catharus berlepschi Lawrence 1888

Trans-Andean nightingale-thrush

(Figs 15–18)

Catharus fuscater Sclater 1859a: 136, 1859b: 324 (in part); Berlepsch and Taczanowski 1884: 283; Salvin 1895, Goodfellow 1901: 309; Meyer de Schauensee 1966: 412 (in part); Meyer de Schauensee 1970: 342 (in part); Ridgley and Tudor 1989: 110 (in part); Clements and Shany 2001: 193; Solano-Ugalde et al. 2007; Schulenberg et al. 2007 (in part); Kikuchi 2009; Schmitt et al. 2013; Astudillo et al. 2015; Remsen et al. 2023 (in part).

Catharus berlepschi Lawrence ‘1887’ (=1888; see: LeCroy 2005: 39): 503; Ridgway ‘1887’: 504; Sharpe 1902: 182.

Catharus fuscater caniceps Chapman 1924: 14; Hellmayr 1934: 466; Bond 1956: 241; Fjeldså and Krabbe 1990: 554 (in part); Collar 2005: 700 (in part); Halley 2020.

Catharus fuscater fuscater Fjeldså and Krabbe 1990: 554 (in part); Clement 2000: 299 (in part); Ridgley and Greenfield 2001: 660 (in part); Collar 2005: 700 (in part).

Catharus fuscater berlepschi Halley 2021: 132 .

Catharus berlepschi nebulus ssp. nov. (formerly Undescribed 3).

urn:lsid:zoobank.org:act: EAE392CC-A763-4E5E-8F6F-68921515C9A2.

Catharus fuscater Taczanowski 1874: 504; 1879: 222; 1882: 4; 1884: 483.

Catharus fuscater caniceps Fjeldså and Krabbe 1990: 554 (in part); Clement 2000: 299 (in part); Collar 2005: 700 (in part).

‘Unnamed-3’ Halley 2021: 133.

Type material

Catharus b. berlepschi: AMNH 39096 (holotype), study skin, adult male, collected by Joseph Siemiradzki in Cayandeled (approximately –2.117°, –78.98°; see: Paynter 1993: 34), Chimborazo, Ecuador, on 23 January 1883 (see: LeCroy 2005: 38). Siemiradzki collected four males and a female, which Berlepsch and Taczanowski (1884: 283) classified as C. fuscater . Berlepsch then sent one of the males (AMNH 39096) to Lawrence, who described it as a new species. For this study, M. R.H. examined the holotype on 20 June 2013 .

Catharus b. caniceps: AMNH 175530 (holotype), study skin, adult male, collected by H. Watkins (no. 6011) at Palambla (approximately –5.23°, –79.37°; see: Stephens and Traylor 1983: 153), Piura, Peru, on 16 September 1922 (see: LeCroy 2005: 39). For this study, M . R.H. examined the holotype on 20 June 2013 .

Catharus b. nebulus ssp. nov.: FMNH 474413 (holotype), study skin, adult male, collected and prepared by David E. Willard on Cerro Monte Alegre (–6.5850°, –77.5617°, elev. 2400 m), Amazonas, Peru, on 23 June 2010. When it was prepared, the holotype weighed 37.5 g. Its testes were not enlarged (1 × 0.5 mm) and the skull was 50% pneumatized. In 2022, the entire dorsal surface was darker than Sepia (119), with the crown slightly darker than the back and rump. The undertail coverts were Dark Drab (119B) and the flanks were darker and cooler than Vandyke Brown (121). The breast was darker than Glaucous (79) with faint mottling. The throat was cooler than Drab-Grey (119D), contrasting with the breast.

Geographic range

Catharus b. berlepschi: Western Andes in Ecuador (Carchi, south to El Oro).

Catharus b. caniceps: Western Andes in Ecuador (El Oro), south to north-western Peru (Cajamarca, La Libertad), and the Huancabamba and Chunchuca valleys, west of the Río Marañón .

Catharus b. nebulus ssp. nov.: Eastern slope of the Peruvian Andes from Amazonas (east of Río Marañón) south to Cusco (north-west of Río Apurímac), including Chachapoyas (Amazonas), Tambillo ( Huamanga), and Chilpes (Junín) between 1770 and 2290 m (Taczanowski 1884).

Adult specimens examined

Catharus b. berlepschi (N = 11): Ecuador (N = 11): Carchi (two males, one female): west slope near Maldonado-Tulcán Rd, along Río La Plata: ANSP 181213 181214 (males), ANSP 181212 (female) ; Chimborazo (three males): Chunchi: ANSP 59755–59757 (males); Pinchincha (three males): Chiriboga: DMNH 59252, 62883 (males); Mindo: AMNH 503903 (male); El Oro (two males, two females): Salvias: AMNH 167890 (male); Zaruma: ANSP 83643 (male), AMNH 130154, ANSP 83644 (females); El Chiral: AMNH 167888 (male) .

Catharus b. caniceps (N = 33): Ecuador (N = 6): Loja (three males, three females): Alamor: AMNH 167894 (female); Celica: AMNH 167891, 167893 (males), AMNH 167892 (female); San Bartolo: AMNH 172116 (male), AMNH 172117 (female) . Peru (N = 27): Piura (four males, four females): Palambla: AMNH 175530–17533 (males), ANSP 116437, 116438, AMNH 175534, 175535 (females) ; Lambayeque (one female): Porculla: ANSP 116441 (female); Cajamarca (six males, one female): Chira: ANSP 116442, 116443 (males); Quebrada Lanchal: LSUMZ 170101, 170102 (males), LSUMZ 170103 (female); Quebrada La Palma: LSUMZ 170104 (male); Cajabamba: AMNH 503909 (male) . La Libertad (eight males, three females): Seques, north-east of Pacasmayo: AMNH 236066, 236068–236070 (males), AMNH 236067 (female); Taulis, north-east of Pacasmayo: AMNH 236071, 236072, 236075, 236076 (males), AMNH 236073, 236074 (females) .

Catharus b. nebulus ssp. nov. (N = 19): Peru (N = 19): Amazonas (two males, four females): 33 km NE of Ingenio: LSUMZ 82159 (female); Cerro Montealegre: FMNH 474413 (male); La Lejia,north of Chachapoyas: AMNH 235051 (male); Leymebamba: ANSP 109278 (female); 20 km E of La Peca: LSUMZ 88630, 88631 (females); Huánuco (three males): Cayumba Alto: FMNH 299304 (male); CordilleraCarpish: LSUMZ 78972, 80744 (males); Junín (onemale): Rumicruz: AMNH 174319 (male); Pasco (four males, four females): Playa Pampa: LSUMZ 129006, 129007, 129011 (males), LSUMZ 129002, 129005 (females); Santa Cruz: LSUMZ 106496 (male), LSUMZ 106495, 106497 (females); San Martín (one female): 22 km ENE of Florida Pomacochas: LSUMZ 174203 (female) .

Immature specimens examined

Catharus b. berlepschi (N = 5): Ecuador (N = 5): Carchi (two females): west slope near Maldonado-Tulcán Rd., along Río La Plata: ANSP 181215 181216 (females); Pinchincha: Chiriboga: DMNH 62882 (male); Mindo Arriba: AMNH 180632 (male); El Oro (two males): Salvias: AMNH 167889 (male); Zaruma: AMNH 130153 (male) .

Catharus b. caniceps (N = 3): Peru (N = 3): Piura (one male, one female): Palambla: ANSP 116439 (male), CM 119947 (female); Cajamarca (one male): Chugur, 65 km north-west of Cajamarca: AMNH 236065 (male); Quebrada Lanchal: LSUMZ 170100 (female) .

Catharus b. nebulus ssp. nov. (N = 1): Peru (N = 1): San Martín (one male): 22 km ENE of Florida Pomacochas: LSUMZ 174204 (male) .

Audio recordings examined

Catharus b. berlepschi (N = 20): Ecuador (N = 20): Azuay: Cuenca: Molleturo, Corona de Oro Rd.: XC 602205; Yunguilla Reserve: ML 135902, 135926, 76216901, XC 19999; Loja: near Celica: XC 67875; Reserva Utuana: ML 141950781, XC 67874; Pichincha: Bellavista, Tandayapa: XC 128440, 13227, 4214; Mindo: XC 545139, 546525; Mindo Cloud Forest: ML 139115; Old Mindo-Nono Rd., before Tandayapa: ML 63456; Recinto 23 de Junio: ML 216745971, XC 186913; Reserva Paz de Aves: XC 30933; Tandayapa Bird Lodge: XC 32386, 54902.

Catharus b. caniceps (N = 4): Peru (N = 4): Cajamarca: Chotas, Bosque Protector Pagaibamba: XC 108771; Sallique: Quebrada Lanchal: ML 515357, 515369 ; Piura: Ayabaca, Bosque de Cuyas: XC 231 .

Catharus b. nebulus ssp. nov. (N = 18): Peru (N = 18): Amazonas: Camino Atuen: ML 398834941; Camp Lowbrow: ML 304312761; Fundo Alto Nieva: ML 72665721; La Llantera cerca de Afluente: ML 272483101; above Leimebamba: XC 175873; Utcubamba: Bagua Grande, ACP Bosque Berlín: ML 129649691, XC 123919; Huánuco: Paty Trail: XC 243435, 243436, 243437; Pasco: Bosque Shollet: ML 228217101, 289516811; Oxapampa: ML 269963401, 376022481; San Martín: Abra Patricia: ECOAN Lodge: XC 30494, 144628; Ucayali: Oventeni: ML 138773; Ulcumano Ecolodge: ML 287691191.

Diagnosis

Genetics: In the UCE tree, samples from (i) western Ecuador and north-western Peru, encompassing the type localities of C. berlepschi Lawrence 1888 and C. f. caniceps Chapman 1924, and (ii) eastern Peru from Amazonas south to the Río Apurímac (C. b. nebulus ssp. nov.), formed reciprocally monophyletic clades. Together, these clades formed the sister-group of a clade composed of samples of C. [f.] opertaneus and Undescribed 2. We treat these major sister-groups as polytypic species: C. berlepschi (including C. b. berlepschi, C. b. caniceps, and C. b. nebulus ssp. nov.) and C. opertaneus (including C. [f.] opertaneus and Undescribed 2, see below). The subspecies C. b. berlepschi and C. b. caniceps were not genetically diagnosable, despite their plumage colour differences. A sample of C. b. berlepschi from the Yunguilla Valley, Azuay, Ecuador (ZMUC 128360) was more similar to a paratype of C. f. caniceps (AMNH 175531) than a sample of C. b. berlepschi from Imbabura, Ecuador (ZMUC 119570). In the ND2 tree, these three samples, plus one sample each from the Huancabamba and Chunchuca valleys (i.e. east of the Abra de Porculla, an east–west pass through the Western Cordillera at 2145 m) and a sample from Loja, Ecuador, formed a clade with low within-clade divergence (mean uncorrected p -distance = 0.005 ± 0.004). Samples from across the range of the eastern Andean group (C. b. nebulus ssp. nov.) also formed a clade in the ND2 tree with low within-clade divergence (mean uncorrected p -distance = 0.002 ± 0.001). The divergence between these sister-clades (C. b. berlepschi + C. b. caniceps, vs. C. b. nebulus ssp. nov.) was an order of magnitude greater (mean uncorrected p -distance = 0.022 ± 0.002) than the mean divergence within either clade. ABGD analysis of ND2 data merged C. berlepschi with Undescribed 2 (uncorrected p -distance = 0.01 ± <0.01), although these were not sister-groups in the UCE tree, while treating C. b. berlepschi and C. b. nebulus ssp. nov. as independent genetic clusters. ASAP analysis merged C. b. berlepschi, C. b. nebulus ssp. nov., and Undescribed 2.

Morphology: Study skins from the range of C. berlepschi in the western Andes were sexually monochromatic in the adult plumage and exhibited a north–south colour cline. At the northern end of the cline, adults had dark dorsal plumage (darker than Sepia, 119), medium-light ventral plumage (Figs 15, 16; Table 3), and completely black maxillae (Table 4), whereas southern adults (C. b. caniceps), including in the Huancabamba and Chunchuca valleys, were paler on the flanks, breast, and throat (Figs 15, 16; Table 3) and had dichromatic irides (Table 5). Specimens from Zaruma, El Oro (ANSP 83643, 83644) had somewhat intermediate characters between the endpoints of the plumage colour cline, and are here listed under the nominate form, C. b. berlepschi . Adult study skins of C. b. nebulus ssp. nov. were dichromatic in iris colour and more similar in plumage colour to C. b. caniceps than C. b. berlepschi . A juvenile specimen identified as C. b. nebulus was morphologically divergent from C. b. berlepschi and C. b. caniceps (see below), but this requires further investigation to confirm.

Voice: The blurred calls of C. b. berlepschi and C. b. nebulus ssp. nov. had a ‘check-like’ sonogram shape, which distinguished them from all other taxa in the complex, including Undescribed 2, which had a downward sloping blurred call that was narrower in bandwidth (Fig. 11). The subspecies C. b. berlepschi and C. b. nebulus ssp. nov. differed in punctuation call structure (Type 2 vs. Type 3, respectively). In song, of the five triadic contours (ABC, ACB, BCA, CAB, CBA) detected in C. b. berlepschi, four (ABC, ACB, BAC, BCA) were shared with C. b. nebulus ssp. nov.; of the four tetradic contours (ACDB, BCDA, CABD, CDBA) detected in C. b. berlepschi, none was shared with C. b. nebulus ssp. nov., and only one (BDAC) was shared with Undescribed 2.

Etymology

We propose the English name ‘Trans-Andean nightingale-thrush’ for the polytypic C. berlepschi because it is the only species in the complex that occurs on both slopes of the Andes. The scientific name C. b. nebulus ssp. nov. is derived from Latin feminine noun nebula (mist, fog), referring to its montane forest habitat.

Comments

We placed the name ‘ C. f. caniceps ’ into the synonymy of C. berlepschi because, in both reconstructions, genetic samples from western Ecuador and north-western Peru formed a clade that encompassed the type localities of both taxa, and the older name has priority. Based on the shallow ND2 divergence between samples from the western Andes, on one hand, and the eastern side of the Abra de Porculla in the Huancabamba (LSUMZ 170103) and upper Chunchuca valleys (LSUMZ 170104) on the other, we hypothesize that C. berlepschi crossed the Abra de Porculla, from the west, sometime after the LGM.

Despite its monophyly in both genetic datasets, we treat the taxon from the eastern Andes as a subspecies of C. berlepschi, instead of its sister-species, because additional sampling is needed to assess the degree of vocal and morphological divergence. We note that C. b. nebulus ssp. nov. is apparently divergent from C. b. berlepschi in juvenile plumage and punctuation call structure, but this may be an artefact of low sample size. Study skins of C. b. nebulus ssp. nov. also exhibit subtle sexual dichromatism, unlike the sexually monochromatic (but clinally variable) C. b. berlepschi + C. b. caniceps clade. Males of C. b. nebulus ssp. nov. (e.g. FMNH 474413, LSUMZ 129006) were darker and less brown on the dorsal surface than adult females, including on the crown, and some adult males of C. b. nebulus ssp. nov. approached the brownish plumage of the adult female (e.g. LSUMZ 106496, with enlarged testes: 9 × 15 mm). This suggests that C. b. nebulus ssp. nov. may exhibit polychromatic plumage ‘types’ like C. [f.] mentalis (see below). Notably, the strongest colour differences between C. b. nebulus ssp. nov. and the C. b. berlepschi + C. b. caniceps clade occur where their ranges approach each other in northern Peru, which may be indicative of character displacement.

The plumage of a juvenile from central Peru (LSUMZ 174204), identified as C. b. nebulus ssp. nov., was boldly marked relative to a juvenile C. b. berlepschi (ANSP 181216). LSUMZ 174204 has tawny streaks on the mantle, tawny spots on the breast, a whitish throat and abdomen, and a pale mandible (Fig. 19). At first glance, this specimen resembles the juvenile of C. maculatus, but there are multiple reasons to doubt that identification. CM 85107, a genuine C. maculatus juvenile from Cochabamba, Bolivia, has a dark mandible (vs. pale with dusky tip in LSUMZ 174204), a darker and more heavily marked belly (vs. white), and a brown ‘collar’ across the upper breast (vs. no collar). LSU 174204 was also collected at 2300 m, at the same site as an adult female C. b. nebulus ssp. nov. (LSUMZ 174203), and about 500 m upslope of the known upper range limit of C. maculatus in central Peru (Schulenberg et al. 2007). As noted by Ridgely and Tudor (1989: 110), C. maculatus and C. [ fuscater] populations in South America ‘seem rarely if ever actually to occur together, rather, replacing each other in an as yet not understood way’.

Freeman et al. (2022) played recordings of C. b. nebulus ssp. nov. in ‘territories’ of C. b. berlepschi and recorded the response of the ‘territorial bird’ (i.e. how closely the playback target approached the speaker, and whether and how much it vocalized). In each of eight different experiments, one recording was played in the vicinity of a singing individual, and three different stimuli were used overall (XC 175873 for two experiments, XC 30494 for three experiments, XC 144268 for three experiments). We reiterate that interpreting the results of these experiments (and ‘sympatric’ experiments using audio playback of C. b. berlepschi recordings in the range of C. b. berlepschi) is not straightforward, because the function of song (and, therefore, any response to it) is not clearly defined in species that exhibit cooperative parental care and/or facultative territoriality (e.g. Goetz et al. 2003, Halley 2014, Greeney et al. 2015, Halley et al. 2016).