[Ornithology • 2019] Pycnonotus pseudosimplex • A Cryptic New Species of Bulbul (Pycnonotidae) from Borneo ---ScRaBBlE

Pycnonotus pseudosimplex

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

DOI 10.25226/bboc.v139i1.2019.a3 

 Abstract  

Cream-vented Bulbul Pycnonotus simplex of Borneo was previously considered to be polymorphic in iris colour, having either red or white (creamy-yellow) irides. Mitochondrial DNA sequence comparisons, however, indicate that white- and red-eyed Bornean individuals are not closely related to one another. Instead, white-eyed birds are sister to Ashy-fronted Bulbul P. cinereifrons of Palawan Island, in the south-west Philippines, and red-eyed birds are sister to white-eyed P. simplex of the Thai-Malay Peninsula. Consequently, we elect to treat the white-eyed Bornean population as a distinct, previously overlooked species. In respect to plumage, white- and red-eyed individuals are almost identical, varying only slightly in the amount of yellow coloration in their feathers. The two taxa are sympatric at some localities, but white-eyed individuals are rarer and more consistently associated with mature forest than red-eyed birds.

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)

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).

Taxonomy.— Genetic comparisons using mitochondrial ND2 sequences reveal that white- and red-eyed individuals of P. simplex from Borneo are not members of the same species. Their segregation by iris colour is backed by a deep ND2 sequence divergence (14%). Red-eyed Bornean birds are sister to white-eyed P. s. simplex of the Thai-Malay Peninsula at 4% ND2 divergence, whereas white-eyed Bornean birds are sister to P. cinereifrons of Palawan at 12% ND2 divergence. The perfect association of ND2 haplotype with iris colour across the region where the two morphotypes co-occur suggests assortative mating and the absence of mitochondrial gene introgression. For the red-eyed Bornean population, iris colour difference is adequate for recognition as a separate subspecies (P. s. perplexus; Chasen & Kloss, 1929, Eaton et al. 2016), or possibly even species, from white-eyed P. s. simplex of the Thai-Malay Peninsula and Sumatra. Because the two taxa are relatively closely related in respect to ND2 distance, species-level reclassification should depend on future research into gene flow and song. Plumage variation is unlikely to be helpful because of the similarity between these populations and the tendency for colours to change in museum specimens (Hoogerwerf 1966, Mees 1986). For the white-eyed Bornean population, its large genetic distance from P. cinereifrons and distinct morphology (Fig. 2) are sufficient to recognise it as a species.

There are no other taxa whose names apply to the Bornean white-eyed population. P. simplex subspecies have been described from Sumatra, the Anamba Islands, the northern Natuna Islands, the southern Natuna Islands, Java, and northern Borneo (Table 1, Fig. 1). Iris colour and size connect white-eyed populations of Sumatra and mainland Asia in subspecies simplex (Fig. 1). Larger size distinguishes the white-eyed subspecies halizonus (including its junior synonym axanthinus) of the Anamba and northern Natuna Islands from other white-eyed populations: e.g., mean wing length for halizonus 83.6 mm (n = 4) vs. 74 mm (n = 12) for Bornean white-eyed individuals. The red-eyed subspecies on the southern Natuna Islands (oblitus) belongs with Borneo's red-eyed population based on iris colour, size and plumage (Mees 1986). Eye colour of the Javan population (prillwitzi) varies from red to orange or red-brown, and its plumage is more distinctive than any other population of P. simplex, including red- and white-eyed Bornean populations (Hoogerwerf 1966). Apart from these taxa of P. simplex, there is no evidence that early taxonomists confused other species of similar-looking bulbuls with the white-eyed Bornean population of P. simplex. Pycnonotus brunneus has two subspecies: P. b. brunneus (including P. b. zaphaeus) and P. b. zapolius. Both of these were described as having red irides. P. erythropthalmos (including P. e. salvadorii, sometimes recognised for Borneo) has a red iris with a yellow eye-ring. Because no name applies to the Bornean white-eyed population, we name it:

Pycnonotus pseudosimplex, sp. nov.

Cream-eyed Bulbul

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.

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.

Subir B. Shakya, Haw Chuan Lim, Robert G. Moyle, Mustafa Abdul Rahman, Maklarin Lakim and Frederick H. Sheldon. 2019. A Cryptic New Species of Bulbul from Borneo. Bulletin of the British Ornithologists’ Club. 139(1) DOI 10.25226/bboc.v139i1.2019.a3 

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