Pycnonotus pseudosimplex, Shakya & Lim & Moyle & Rahman & Lakim & Sheldon, 2019

Shakya, Subir B., Lim, Haw Chuan, Moyle, Robert G., Rahman, Mustafa Abdul, Lakim, Maklarin & Sheldon, Frederick H., 2019, A cryptic new species of bulbul from Borneo, Bulletin of the British Ornithologists’ Club 139 (1), pp. 46-55 : 52-54

Pycnonotus pseudosimplex , sp. nov.

Cream-eyed Bulbul

Holotype.— Study skin, Louisiana State University Museum of Zoology ( LSUMZ 188187 ), Baton Rouge ; tissue, LSU Museum of Natural Science ( LSUMNS B-84971); adult male; Malaysia, Sarawak, Miri Division , Miri, Lambir Hills National Park, 04°12’N, 114°25’E; elevation c. 120 m (from Google Earth); habitat: secondary forest continuous with old-growth hill forest; collected 23 April 2013; prepared by Frederick H. Sheldon ( FHS), original catalogue number FHS 1022; photo by John Mittermeier ( Fig. 3A ); GenBank accession no. MK298058 .

Diagnosis.—The iris of P. pseudosimplex is creamy yellow instead of crimson-red as in Cream-vented Bulbul P. s. simplex of Borneo. Its plumage also differs from that of P. s. simplex in being yellower on the throat and vent, creating greater contrast with the darker breast and flanks. From P. cinereifrons , P. pseudosimplex differs in being much smaller: P. cinereifrons mean 31.7 g (n = 3); P. pseudosimplex mean 20.7 g (n = 11). P. cinereifrons also has an olive tinge to the leading edge of its remiges, which is especially obvious on the folded wings of specimens (similar to P. plumosus of Borneo). From P. brunneus , P. pseudosimplex differs in having a white iris instead of an orange or two-toned iris. Similarly, P. erythropthalmos differs in having a dark red iris and a circle of yellow skin around the eyes.

Description of holotype.—Approximate colour names used for description, with standard colour names from Ridgway (1912) and alphanumeric colour codes from Munsell (1950) in parentheses. Crown, nape and back uniform olive-brown (Olive Brown; 5Y3/4) becoming yellower on rump and uppertail-coverts (Dresden Brown; 2.5Y4/4). Tail dark brown (Chestnut Brown; 10YR3/2). Cheeks similar in colour to crown (Olive Brown; 5Y3/4) with paler shaft-streaks to feathers. Throat pale yellow (Olive Buff; 5Y8.5/4); breast slightly darker than throat with darker olive-brown diffuse streaks (5Y4/2). Flank feathers olive (Light Brownish Olive; 2.5Y5/6). Undertail feathers cream-coloured (Naples Yellow; 5Y7/6). Wing like tail (Chestnut Brown; 10YR3/2) with olive-yellow edges. Soft part colours recorded on collection: bill black; iris creamy yellow; legs and toes dark brown. No moult; testis 2 × 1 mm, skull: 100% ossified; stomach: full of fruit with 1 mm-long seeds.

Measurements of type.—See Table 3.

Paratypes.—We designate 11 paratypes, which include specimen LSUMZ 181671 and ten specimens held at WFVZ: 38742, 38743, 38746, 38747, 38754, 38775, 38776, 38778, 38780, 38782 (listed in Table 3). The paratypes were collected in various parts of Sabah, Malaysian Borneo (unlike the holotype, which was taken in Sarawak, Malaysian Borneo ). Measurements of all paratypes and their iris colours are reported in Table 3 .

Etymology.—For more than 100 years this species has been confused with P. simplex , i.e., since Carl Lumholtz collected the first white-eyed specimen in ‘Boeloengan’ (Balungan Regency) along the Kayan River in eastern Kalimantan, Indonesian Borneo, in 1914 ( Lumholtz 1920, Voous 1961). Apart from eye colour, the two species are almost indistinguishable; hence, we refer to the new species as ‘false’ or ‘pseudo’ simplex . The common name, Cream-eyed Bulbul, describes the main identifying character of the new species. It also evokes a time when P. simplex was known as the White-eyed Brown Bulbul, as opposed to the Red-eyed Brown Bulbul P. brunneus of Borneo ( Smythies 1960).

Habitat.— P. simplex and P. pseudosimplex appear to be sympatric in mature forest interior and edge. Individuals of both species whose DNA was compared in this study were collected in the same localities during recent years: viz., Ulu Kimanis, Crocker Range National Park, Sabah, in 2008; Lambir Hills National Park, Sarawak, in 2013; and Batang Ai National Park, Sarawak, in 2018 ( Fig. 1 , Table 2 ). Both taxa were also mist-netted together in the early 1980s elsewhere in Sabah: at Bole River, Saliwangan Baru, and Mangkatai (Megatai) (localities described in Sheldon 2015). Although previous authors have stated that white- and red-eyed individuals co-occur throughout Borneo ( Hoogerwerf 1966, Mees 1986), our experience and specimen records suggest that white-eyed individuals are considerably rarer and perhaps more habitat-restricted. P. simplex occurs to 1,100 m (Kelabit Highlands) and in several forest types of varying quality: good-soil dipterocarp, kerangas and peatswamp; primary, secondary, and heavily disturbed forest; and plantations. We have found P. pseudosimplex (only by mist-netting) to 500 m (Ulu Kimanis) near the edge of mature good-soil dipterocarp, and in kerangas forest nearer to sea level.

Morphology and voice.—Given their distinct ancestry, the striking similarity in plumage between P. simplex and P. pseudosimplex is remarkable. This is particularly true in specimens, less so in photographs ( Fig. 3 ). They also closely resemble other species of brown bulbuls on Borneo to which they are not especially closely related: Red-eyed Bulbul and Spectacled Bulbul ( Fig. 2 ). Perhaps these species are strongly selected for the cryptic advantage of dull brown plumage, but that observation does not hold for other bulbuls that occasionally occupy forest-edge habitat, such as Black-headed P. atriceps and Yellow-vented Bulbuls P. goiavier , which are both much more brightly coloured.

We are unaware of any vocal differences between P. simplex and P. pseudosimplex , although we would expect some. P. simplex is far more common than P. pseudosimplex and thus more likely to be represented in sound archives, but without accompanying iris colour data it is currently impossible to know which species is vocalising in recordings. In general, all of Borneo’s brown bulbuls have similar songs that are not as distinctive (to the human ear) as Black-headed, Yellow-vented, or other species of bulbuls. Although vocalisations are certainly important, eye colour might be the main trait for species recognition among brown bulbuls. This has been observed in Streak-eared Bulbul P. blanfordi of Indochina and the Thai-Malay Peninsula ( Garg et al. 2016). A large mitochondrial distance occurs between two vocally and visually similar subspecies, P. b. blanfordi and P. b. conradi, which are also most easily distinguished by iris colour: P. b. blanfordi has dark red irides, whereas P. b. conradi usually has dark grey irides ( Garg et al. 2016). On Borneo, field comparisons of P. pseudosimplex with other brown bulbuls—especially how the species use their markedly distinct eye colours—are likely to yield rich information on the behavioural ecology of an otherwise generally under-appreciated group of birds.

Figures

Figure 1. Map of Sundaland showing range of Cream-vented Bulbul Pycnonotus simplex with labelled type localities of subspecies from Table 1 and the collecting sites of P. simplex specimens whose ND2 was sequenced.

Figure 2. Maximum likelihood tree generated from mitochondrial ND2 sequences. Numbers adjacent to branches indicate bootstrap support. Illustrations of heads of each species are shown to the right (depictions by Subir B. Shakya).

Figure 3. Photographs from Lambir Hills National Park, Miri Division, Sarawak, Malaysia of (A) Cream-eyed Bulbul Pycnonotus pseudosimplex sp. nov., and (B) Cream-vented Bulbul P. simplex (© John C. Mittermeier)