The Large-billed Reed Warbler Acrocephalus orinus revisited Bensch, Staffan; Pearson, D Published in: Ibis DOI: 10.1046/j.1474-919X.2002.00036.x 2002 Link to publication Citation for published version (APA): Bensch, S., & Pearson, D. (2002). The Large-billed Reed Warbler Acrocephalus orinus revisited. 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LUND UNIVERSITY PO Box 117 221 00 Lund +46 46-222 00 00 IBI_036.fm Page 259 Thursday, March 7, 2002 8:22 PM Ibis (2002), 144, 259–267 Blackwell Science Ltd The Large-billed Reed Warbler Acrocephalus orinus revisited STAFFAN BENSCH1* & DAVID PEARSON2 1Department of Animal Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden 24 Lupin Close, Reydon, Southwold, Suffolk IP18 6NW, UK The Large-billed Reed Warbler Acrocephalus orinus is known only from the type specimen, collected in Himachal Pradesh, India, in 1867. The specimen is poorly prepared, and it has been suggested that it could represent an isolated form of the Clamorous Reed Warbler A. stentoreus or an aberrant Blyth’s Reed Warbler A. dumetorum. We tested the affinity of A. orinus by (1) re-examining the morphology of the type specimen and (2) amplifying and sequencing a portion of its mitochondrial cytochrome b gene. Both the morphological and the mitochondrial analyses showed the specimen to be similar to dumetorum, but distinct enough to qualify as a species of its own. Relative to dumetorum, it has a more rounded wing, longer bill, longer and more graduated tail with more pointed tail feathers, and larger claws. The divergence in mitochondrial DNA between orinus and dumetorum was 7.8%, well above the value expected between subspecies. A. orinus is smaller than any of the forms of A. sten- toreus or the related Australian Reed Warbler A. australis. It has a somewhat longer first primary, more pointed tail feathers and paler, less robust feet and claws. DNA comparison places it in the clade of small unstreaked Acrocephalus warblers, and apart from the clade of large unstreaked warblers that contains stentoreus and australis. In recent decades, there have been more discoveries until 1885 when this came in its entirety to the of new bird species (Vuilleumier et al. 1992) than British Museum (BMNH). The specimen was first anyone would have dared to anticipate in the middle provisionally described as Phyllopneuste macrorhyncha of the last century (Mayr 1957). This is partly (Hume 1869) but the name was changed two years later because of the increasing skill of the many bird- to Acrocephalus macrorhynchus Hume, 1871 when its watchers nowadays travelling to remote areas, and generic affinity was established. However, Oberholser also due to technical improvements, such as audio (1905) pointed out that this latter name was unten- recording systems and sonagram analyses (Whitney able because a specimen from Egypt, described by & Alvarez Alonso 1998) and PCR-based DNA von Müller in 1853 as Calamoherpe macrorhyncha, analyses (Smith et al. 1991, Helbig et al. 1995). appeared to be a synonym of Clamorous Reed Several species of warblers have recently been dis- Warbler Acrocephalus stentoreus. Hence, Acrocephalus covered in southern Asia (e.g. Alström et al. 1992, macrorhynchus was abandoned in favour of the new Olsson et al. 1993, Alström & Olsson 1999) where name Acrocephalus orinus Oberholser, 1905. many cryptic species perhaps remain to be found Describing a new species from just one different- (Price 1996). In this paper we re-examine a (pos- looking individual might be questionable (LeCroy sible) cryptic species from the Himalayas known & Vuilleumier 1992), since it might be an aberrant only from the type specimen, the Large-billed Reed example of an already known species, or a hybrid. Warbler Acrocephalus orinus. This specimen (BMNH This concern has followed A. orinus ever since it was registration no. 1886.7.8. 1742) was collected on first described. Most handbooks and lists do recog- 13 November 1867 in the Sutlej Valley near Rampoor nize it as a species, but usually add a question mark (31°26′N, 77°37′E), Himachal Pradesh, by Allan to this treatment. Details and measurements of the Hume (Hume 1869). It remained in his collection species were given by Vaurie (1955) and Williamson (1968). Vaurie concluded that it was closely related *Corresponding author. to the Blunt-winged Warbler A. concinens and the Email: [email protected] Paddyfield Warbler A. agricola, but remarked on the © 2002 British Ornithologists’ Union IBI_036.fm Page 260 Thursday, March 7, 2002 8:22 PM 260 S. Bensch & D. Pearson long, broad bill, larger and less attenuated than in MORPHOLOGY AND those species, or indeed the larger Blyth’s Reed MEASUREMENTS Warbler A. dumetorum. He described the rounded wing structure, with a short second primary as in The specimen is poorly prepared, so that the under- concinens, but with the third and fourth primaries parts are ‘cramped’ and badly displayed. The tail is also short of the fifth. Williamson considered this twisted, with the feathers broken off on one side, but unusual wing formula to be due to incomplete feather with a full set examinable on the other. It appears to growth. He pointed out that the bird was still in be completing moult with sheaths still present at the moult and noted traces of waxy sheaths on the outer base of some of the underpart feathers, but we were primaries. He concluded that the wing formula unable to confirm the presence of sheaths on the details were therefore unhelpful, and that wing and outer primaries of either wing. The secondaries and tail were probably short of their fully grown length. tail feathers all appear to be fully grown. He suggested that the bird ‘might represent a rare The upperparts are rich olive-brown, with a slight and isolated form of the widely but patchily distrib- rufous tinge, especially on the upper tail-coverts. The uted A. stentoreus’. underparts are strongly washed with olive-buff, although The present study took shape when one of us a degree of staining may be involved. The sides are (D.P.) briefly inspected the type of A. orinus at the more olive brown, and the throat is paler creamy olive. Natural History Museum, Tring, and noted its close A pale superciliary stripe is evident in the specimen resemblance to a moulting Blyth’s Reed Warbler but does not seem to be strongly pronounced. Colora- A. dumetorum. Other warbler specialists have also tion is close to that of freshly moulted A. dumetorum apparently been struck by this similarity (Per specimens from Indian wintering grounds, but these Alström, Urban Olsson and Lars Svensson pers. are somewhat more olive, less rufous-tinged, and comm.). We decided to re-evaluate the species status slightly paler. The upper mandible is dark, but the of the specimen by (1) remeasuring it carefully cutting edges and entire lower mandible are pale. together with a representative number of A. dumeto- The tarsi, toes and claws appear pale brown. rum, A. concinens and appropriate forms of the Measurements and wing structure details of the A. stentoreus/australis complex, and (2) identifying a specimen are given in Table 1, and compared with portion of its mitochondrial cytochrome b sequence. those of dumetorum and some other potentially We expected to find that both morphological char- related taxa. A. orinus clearly has a longer tail and acters and the cytochrome b sequence data would larger feet and claws than dumetorum. The bill is fall within the variation observed in dumetorum, so longer, stronger and slightly broader than in dumeto- that Acrocephalus orinus could be safely removed rum and tapers less toward the tip (Fig. 1a,b). As from the list of extant or extinct bird species. To our pointed out by Vaurie (1955) the rictal bristles are surprise, this hypothesis proved to be wrong. shorter and weaker. Table 1. Measurements and structure of the Acrocephalus orinus type specimen compared with those of A. dumetorum, A. concinens haringtoni, A. australis sumbae and A. stentoreus brunnescens. Reported are mean (range) for 10 of each (males and females). All measurements (in mm) taken by D.P. orinus dumetorum haringtoni sumbae brunnescens wing 61 62.2 (60–64) 57.4 (55–59) 68.2 (65–70) 88.8 (87–91) tail 57 51.0 (48–52) 56.3 (53–59) 62.1 (60–64) 80.6 (77–83) tarsus 23.5 22.3 (22–23) 21.9 (21.5–22.5) 24.3 (23.5–25) 29.8 (29–31) bill (to skull) 19.5 17.5 (16.5–18) 14.9 (14–15) 20.0 (19.5–21) 25.4 (24.5–27) bill (to rear of nostril) 12.2 11.0 (10–11.5) 9.7 (9–10) 13.4 (12.5–14) 16.6 (16–17) bill width (across rear of nostril) 4.6 4.2 (4.0–4.6) hindclaw 7.2 5.2 (5–5.5) 6.4 (6–7) 8.6 (8–9) 9.3 (9–10) hallux 8.5 7.1 (7–7.5) 7.5 (6.5–8) 9.9 (9–10.5) 11.4 (11–11.5) tip of 2nd p.