467.

Thick-thumbed Myotis

Myotis rosseti

French: Murin de Rosset / German: Kambodscha-LangfuRfledermaus / Spanish: Ratonero de Rosset

Taxonomy. Glischropus rosseti Oey, 1951,

Cambodia.

Subgenus Myotis; horsfieldii species group. See M. ridleyi . Based on neighbor-joining tree analysis in 2008, Myotis rosseti (partly as ndleyr) was related to M. cf. browni (as muricola) and some “long-footed” Myotis (e.g. hasseltir). Monotypic.

Distribution. S & SE Thailand, Cambodia, S Laos, C & S Vietnam (Ha Tinh Province and Cat Tien Nadonal Park); in S Vienam, it might occur in nearby Binh Phuoc Province where “bamboo” habitat occurs.

Descriptive notes. Head-body 36-47 mm, tail 32-42 mm, ear 11-14 mm, hindfoot 5-1-7- 5 mm, forearm 27- 5-31 mm; weight 3-8- 6 g. The Thick-thumbed Myotis has thick pinkish pads on thumbs and small triangular pads on feet. Fur is relatively short, light gray to dark grayish brown on upperparts, with hairs having dark brown bases and pale tips. Underparts are lighter. Ears are gray, long, and funnelshaped, with distinctive emargination on outer margins. Tragus (6-2-6- 8 mm) is ¢.50% of ear length, thickened at base, and angled forward, tapering to tip. Muzzle and limbs are pinkish and not especially pigmented. Wing membrane is dark gray, and uropatagium is attached just below ankle. Calcar lobe is more or less developed. The Thick-thumbed Myotis differs from other species of Myotis by thickened pads on thumbs and feet and absence of P’ and P,. Ridley’s Myotis ( M. ridleyi) and the Thick-thumbed Myotis can be readily recognized among other Myotis by their expanded, globose braincase, shortened, massive rostrum, and reduced premolar number. Glischropus spp. have shorter and broader ears, smaller and more rounded tragus, smaller and pinker thumb and foot pads, and distinctive upperincisors. Ridley’s Myotis is more blackish and lacks thumb pads. Characteristic thumb and foot pads of the Thick-thumbed Myotis also are found in one or more species of Pipistrellus, Glischropus, Eudiscopus, Tylonycteris, and Hesperoptenus . These distinctive morphological features also suggest Thick-thumbed Myotis are confined to bamboo associations. Baculum of a Thick-thumbed Myotis from southern Vietnam was moderately large (1- 1 mm in length), relatively wide, and weakly converging forward, with wide rounded tip; border between main body and “wings” was not apparent, and thickened edges were absent; upper side was concaved and had large rounded protrusion in basal one-third hanging over wide and shallow basal notch; and urethral groove was wide and deep. Skull is similar to that of Ridley’s Myotis, but braincase is a little more swollen frontally; interorbital region is shorter; rostrum is slightly shorter and wider, median depression is shallower and less clearly defined; narial emargination is more nearly U-shaped rather than V-shaped as in Ridley’s Myotis, not extending as far posteriorly; basial depressions more pronounced. Dentition of the Thick-thumbed Myotis is reduced with only 34 teeth. P* and P, are lacking. I? is short and wide and has anterior and posterior cusp, the former cusp is prominent and twice the height of the latter. I is ¢.50% the size of I,. Canines have strong cingulum but no prominent cingulum cusps and are only slightly taller than posterior premolars. Condylo-canine lengths are 10-5-11- 3 mm; maxillary tooth row lengths are 4-1-4- 5 mm.

Habitat. Densely forested mountain slopes, narrow valleys, and turbulent boulder strewn rivers (northern Vietnam), semi-open landscapes with large number of tall bamboo (southern Vietnam), disturbed habitats, and urban areas up to elevations of ¢. 500 m. Recent captures suggest that the Thick-thumbed Myotis is confined to bamboo associations and particularly adapted to using bamboo stems. In Thailand,it roosted in tree hollows, house roofs, and bamboo.

Food and Feeding. The Thick-thumbed Myotis is known to forage for insects over disturbed areas including fields.

Breeding. In Cat Tien, male Thick-thumbed Myotis with enlarged testes were observed in April-May and a pregnant female in November. Females captured in Vietnam in November had conspicuous evidence of post-lactation, suggesting late summer or early autumn birth and thus polyestrous reproduction.

Activity patterns. In Cat Loc (Cat Tien National Park), the Thick-thumbed Myotis foraged c. 1-2 m aboveground among thickets and over cornfields in semi-disturbed and agricultural landscapes. An interesting community of bats adapted to living in bamboo stems, including poorly known species such as the Thick-thumbed Myotis, the Indochinese Thick-thumbed Bat ( Glischropus bucephalus), and the mysterious Disk-footed Bat ( Eudiscopus denticulus), occupy extensive bamboo-dominated formations in Cat Loc.

Movements, Home range and Social organization. Heavy infestations of ectoparasites (nycteribiid flies) on Thick-thumbed Myotis suggest gregarious habits.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Extent of occurrence of the Thick-thumbed Myotis is greater than 20,000 km 2, and recent evidence shows thatit has a wider distribution than was previously known. It has been reported in disturbed habitat and urban areas in some parts ofits distribution suggesting that it is tolerant of disturbance. Its populations are not believed to be declining fast enough to qualify for listing in a more threatened category.

Bibliography. Amador et al. (2018), Bates et al. (1999), Borisenko & Ivanova (2003), Borisenko & Kruskop (2003), Borisenko, Kruskop & Ivanova (2008), Corbet & Hill (1992), Csorba, Bumrungsri & Bates (2008), Francis (2008a), Francis et al. (2010), Hill (1969a), Hill & Topal (1973), Kock (2000), Koopman (1994), Kruskop (2013a, 2013b), Lekagul & McNeely (1988), Oey (1951), Pearch & Writer (2009), Ruedi et al. (2013), Simmons (2005), Thomas et al. (2013), Thong Vu Dinh (2015).