The vespertiolinid bats (family Vespertilionidae) are the most widespread bats worldwide (approximately 300 species) with 41 species from 14 genera occurring on Borneo Island, namely Arielulus, Falsistrellus, Glischropus, Hesperoptenus, Myotis, Philetor, Pipistrellus, Scotophilus, Tylonycteris, Murina, Kerivoula, Harpiocephalus, Phoniscus and Hypsugo (Phillipps and Phillipps 2018).

Hypsugo vordermanni, the white-winged pipistrelle was first described as Vesperugo vordermanni (Jentink, 1890c) from Belitung Island, Indonesia. It is a small-sized bat with a forearm recorded at 30.5 mm and a tail of 15.1 mm. It is a rare bat with only six specimens recorded from Samunsam, Sarawak (Payne et al. 1985, Francis and Hill 1986), Tanjung Puting, Kalimantan (Nash and Nash 1987), Belitung Island, Indonesia (Corbet and Hill 1992, Lim et al. 2016), Belalong, Brunei (Cranbrook and Edwards 1994), Banggi Island, Sabah (Nor 1996), and Kuching, Sarawak (Abdullah et al. 2000, Abdullah et al. 2010).

Until recently, it was included within Pipistrellus, from which Hypsugo differs in terms of its skull characteristics: smaller anterior premolar, shorter rostrum, smaller incisor and canine, with a myotodont pattern of the lower molars and broad and short baculum (Horáček and Hanák 1986, Francis 2008). H. vordermanni is described as having pale reddish-brown fur with darker bases, with large ears and a slightly hatchet-shaped tragus. The most prominent characteristic of this species is its translucent white wings, which become greyer near its body. Its anterior upper premolar is tiny and displaced inwards, which results in the canine and second premolar touching. It is similar to the Least Pipistrelle, P. tenuis, which has darker wings and a narrower tragus (Payne et al. 1985). H. vordermanni is also morphologically similar to H. macrotis, albeit the latter being relatively larger (Lim et al. 2016). It is noted that H. vordermanni feeds on insects and fish in rivers and calm seas (Phillipps and Phillipps 2018).

On 12 November 2018, a specimen of H. cf. vordermanni was caught in the mist net deployed across a stream near the village road in Mantailang, Crocker Range Park, Sabah, located at 5°10'15.13"N, 115°56 4.41"W (Fig. 1 and Fig. 2). The specimen was measured for its external characteristics, including: forearm length (FA), ear length (E), tragus length (TR), tibia length (TB), hind-foot length (HF), tail ventral length (TVL) and weight (Wt). Measurements were taken using the Mitutoyo Digital Caliper 500-196-30 (Mitutoyo, Japan) and weights were taken using a Pesola spring balance (Pesola AG, Sweden). Identification was done, based on keys in Payne et al. (1985).

Figure 1.  

A map showing the location of Mantailang in Sabah, northeast Borneo. Mantailang is an area located near a village road within the border of the Crocker Range Park, a conservation area governed by the Sabah Parks in Sabah, Malaysian Borneo.

Figure 2.  

A mist net was deployed across a river stream at the forest edge where the specimen was caught.

This is a new distributional record for H. cf. vordermanni in Sabah, Malaysian Borneo. This specimen is an adult, pregnant female, with external measurements of FA 33.58 mm, E 10.1 mm, TR 4.91 mm, TB 15.19 mm, HF 8.34 mm, TVL 35.68 mm and Wt 5.8 g (Fig. 3). It is a poorly known and rare species due to its very low capture rate and is categorised as Data Deficient by the IUCN (Görföl et al. 2016). The key characters which suggest specimen identification as H. cf. vordermanni is the translucent white wings and the hatchet-shaped tragus.

Figure 3.  

Side profile of H. cf. vordermanni from Mantailang, Crocker Range Park, Sabah, Malaysian-Borneo. The hatchet-shaped tragus is one of the indicative features of this genus.

In Asia, only five species of Vespertilionidae bats are characterised by their "whitish' wings ("almost translucent" and "semi-translucent" included), including Hypsugo vordermanni, H. macrotis, Kerivoula pellucida, K. hardwickii and Myotis macrotarsus (Rydell et al. 2020). The Kerivoula spp. are easily identified by their woolly fur, funnel-shapped ears, with long and pointed tragus. Meanwhile the Myotis spp. have shorter fur and forward-bent tragus (Phillipps and Phillipps 2018).

Hill (1983) and Francis and Hill (1986) remarked that H. vordermanni may be conspecific with H. macrotis, although the possibility of these two being distinct species was also acknowledged (Corbet and Hill 1992). It is noted that both H. macrotis and H. vordermanni have large ears and translucent wings (Fig. 4), with H. macrotis being relatively larger in size (Francis 2008).

Figure 4.  

The white translucent wing of H. vordermanni against a white cloth as a background.

Translucent or whitish wings are suggested to function as camouflage against lit background, thus indicative of the species being an open space aerial forager (Rydell et al. 2020). H. macrotis is suggested to be an edge species (Lim et al. 2016), while the specimen described here was caught on the stream located in an open area at the forest edge near a village road.

A previous study recorded H. macrotis to have a forearm (FA) range of between 31.7 and 34.5 mm (n = 14), while H. vordermanni FA ranged from 31.0 to 33.4 (n = 2) (Lim et al. 2016). A recent study showed that cranial and craniodental characteristics between these two species slightly differ, where H. macrotis has a longer skull in comparison to H. vordermanni (Lim et al. 2016). The specimen described here showed a FA measurement exceeding the range for H. vordermanni by 0.18 mm and overlapped with the FA measurement for H. macrotis. However, the FA measurement range for H. vordermanni is based on only six (6) specimens (Table 1) and this is not comprehensive enough to represent the whole species. However, it is noted that additional specimen collection and retrieval of molecular data with detailed information on its ecology is a priority for confirming the species identification. Nevertheless, as of today, there is no known record of H. vordermanni from Peninsular Malaysia and vice versa for H. macrotis from Borneo. Therefore, it is concluded that the specimen recorded in this study is H. cf. vordermanni.

It is a limitation for the current study that no skull measurement is available for the individual captured as it was released as it was a pregnant individual. No molecular data are available for the individual described here, thus limiting the verification options. Nevertheless, findings from this study contributed to additional distribution data of H. vordermanni in Sabah. More sampling efforts targeting the streams or water bodies near the forest edge or open areas are suggested to obtain more data on this rare or elusive species.

This project was sponsored by Nagao Environment Foundation (NEF), Japan Research Grant (GLA0015-2018), awarded to NHH on 28 March 2018. The field samplings for this study were conducted with permission from Sabah Parks, the statutory body governing CRP, under the permit reference TTS/IP/100-6/2 Jld. 10 (97) (NHH) and SaBC Access Permit JKM/MBS.1000-2/2 JLD.8 (156) (NHH). The authors would also like to acknowledge all the entities and individuals who were involved in the Sabah Parks Mantailang Scientific Expedition in 2018, during which the sampling in this study was conducted. Special thanks to Dr. Juliana Senawi (UKM) and Mr. Isham Azhar (TTU USA) for species reference; Prof. Gabor Csorba (Hungarian NHM) and Dr Lim Lee Sim (USM) for insightful comments and help on the specimen information; and PM Dr Faisal Ali Anwarali Khan (UNIMAS) for suggestions and comments on the manuscript.

Universiti Malaysia Sabah, Sabah Parks

Manuscript writing: NHH; Data collection: NHH, USD, AA, MFMJ, JG, YTFT; Map preparation: LYC; Photographs: USD, AA