New records and an updated checklist of snakes from Son La Province, Vietnam

Abstract Background Son La Province is located in north-western Vietnam and the province contains a large area of 440,000 hectares of natural forest. A wide range of elevations and the complexity of landforms have given this province a great diversity of natural habitats and a high level of biodiversity potential. However, the snake fauna of Son La province is still poorly studied. Previous studies documented 56 species of snakes from this province. New information As a result of our field surveys in Phu Yen, Song Ma, Thuan Chau and Van Ho districts, we report five species of snakes for the first time from Son La Province, northern Vietnam, namely Boiga cyanea, B. guangxiensis, Lycodon meridionalis (Colubridae), Protobothrops cornutus and P. mucrosquamatus (Viperidae), with novel data about morphological characters. In addition, we provide an updated checklist of 61 snake species from Son La Province. The snake fauna of Son La Province also contains a number of species of conservation concern: 11 species listed in the Red Data Book of Vietnam (2007), four species listed in the IUCN Red List (2020) and four species listed in the Vietnam Governmental Decree No. 06 (2019).

Snakes were collected by hand between 08:00 and 22:00 h. After taking photographs in life, snake individuals were euthanised in a closed vessel with a piece of cotton wool containing ethyl acetate (Simmons 2002), fixed in 85% ethanol and then transferred to 70% ethanol for permanent storage. Road-killed snakes were also collected for morphological analysis. Voucher specimens were subsequently deposited in the collections of the Tay Bac University (TBU), Son La Province, Vietnam.
Morphological characters. Measurements, except body and tail lengths, were taken with a slide-calliper to the nearest 0.1 mm in preserved specimens; all measures on body were measured to the nearest millimetre. The number of ventral scales was counted according to Dowling (1951). The number of dorsal scale rows were counted at one head length behind head, at midbody (i.e. at the level of the ventral plate corresponding to half of the total ventral number) and at one head length before vent, respectively. The terminal, pointed scute was not included in the number of subcaudals. Values for symmetric head characters were given in left/right order. The following abbreviations were used: SVL: Snout-vent length, TaL: Tail length.

Distribution
In Vietnam, this species has been recorded from Lao Cai Province in the north, southwards to Ho Chi Minh City (Nguyen et al. 2009, Ziegler et al. 2010). Elsewhere, this species is known from India, Bangladesh, Bhutan, Nepal, China, Myanmar, Laos, Thailand, Cambodia and Malaysia (Nguyen et al. 2009, Ziegler et al. 2010.

Ecology
The voucher specimen was collected at 19:30 h on the ground. The surrounding habitat was secondary forest, composed of small hardwoods, lianes and shrub. Air temperature was 25-30 C and relative humidity was 70-75%.
Colouration in life: dorsal surface grey, with dark spots on the anterior body; dorsolateral side light brown on anterior body; belly whitish anteriorly, grey posteriorly ( Fig. 3). o

Distribution
In Vietnam, this species has been recorded from Lai Chau and Lao Cai provinces in the north, southwards to Kon Tum and Lam Dong provinces (Nguyen et al. 2009). Elsewhere, this species is known from China and Laos (Nguyen et al. 2009).

Ecology
The voucher specimen was collected at 20:50 h on a tree branch, approximately 1.0 m above the ground. The surrounding habitat was disturbed evergreen karst forest of medium hardwood and shrub. Air temperature was 25-30°C and relative humidity was 70-75%.
Colouration in life: dorsal surface black, with 122 narrow yellow cross-bars on body and 35 on tail, bifurcated on the sides, enclosing dark spots; head dark black with symmetrical light markings, the most conspicuous being the one running from the eye to the margin of the snout and another stretching from the hind margin of the parietals; belly cream; lower surface of tail dark brown (Fig. 4).

Distribution
In Vietnam, this species has been reported from Lao Cai and Ha Giang provinces in the north, southwards to Thanh Hoa Province (Nguyen et al. 2009, Ziegler et al. 2014, Nguyen et al. 2018, Nguyen et al. 2016, Nguyen et al. 2018). Elsewhere, the species has been reported from China and Laos (Nguyen et al. 2009, Ziegler et al. 2014, Nguyen et al. 2016, Nguyen et al. 2018).

Ecology
The voucher specimen was found at 09:10 h on the ground. The surrounding habitat was secondary forest composed of medium and small hardwoods, lianes and shrub. Air temperature was 27-32°C and relative humidity was 65-70%.

Description
Morphological characters of the voucher specimen from Son La Province agreed well with the description of Herrmann et al. (2004) and Luu et al. (2015): SVL 610 mm, TaL 146 mm (n = 1); body elongated; head triangular, distinct from neck, flat, covered by small scales; snout obtuse; rostral scale triangular, not visible above; nasal single, subrectangular; loreals 3/3, between nasal and preocular scale; loreal pit bordered by second supralabial and two preocular scales; supralabials 10/10, first completely separated from nasal, third supralabial largest, concave in the middle; horns including one enlarged scale and two relatively-enlarged supraoculars; supralabials separated from suboculars by 2 scales; infralabials 13/12, the first pair in contact with each other, the first three pairs in contact with the chin shields; dorsal scale rows 21-21-17, keeled; ventral scales 190; subcaudal scales 71, all paired; cloacal entire.
Colouration in life: dorsal head grey with dark brown marks; one stripe each side from posterior orbit to edge of the labial; dorsal surface grey-brown with serial blotches along the midbody; dorsolateral side light brown; ventral surface greyish-blue (Fig. 5).

Distribution
In Vietnam, this species has been reported from Lai Chau and Lao Cai provinces in the north, southwards to Quang Binh and Thua Thien Hue provinces (Nguyen et al. 2009). Elsewhere, the species has been reported from China (Nguyen et al. 2009).

Ecology
The voucher specimen was found at 20:35 h on the ground. The surrounding habitat was secondary forest composed of medium and small hardwoods, lianes and shrub. Air temperature was 25-30°C and relative humidity was 70-80%.

Description
Morphological characters of the voucher specimens from Son La agreed well with the descriptions of Stuart and Heatwole (2008), Nguyen et al. (2011, Nemes et al. (2013) and Nguyen et al. (2018): SVL 870 and 950 mm, TaL 220 and 235 mm (n = 2); head triangular, clearly distinct from the neck; nasal undivided; internasals separated from each other by three scales; singe loreal pit; two small scales between the nasal and the shield bordering the anterior region of the loreal pit; postoculars 2/2; supralabials 9-11/9-11, the third large, fourth and fifth separated from the subocular by two scales; temporals small; infralabials 12-13/13-14, the first pair in contact with each other, the first three pairs in contact with the chin shields; dorsal scale rows 27-25-19, rhomboid, strongly keeled throughout, but smooth on the first outer row; ventrals 212-217 (+2 preventrals); cloacal undivided; subcaudals 94 and 99, divided.
Colouration in life: dorsal head brown, paler below; dorsum greyish-brown, with a series of large brown, dark-edged spots; a dark brown line from the eye to the angle of the mouth, edged in black; ventral surface brownish with white blotches; dorsal tail light brown, with a series of conspicuous black spots (Fig. 6).

Distribution
In Vietnam, this species has been reported from Lao Cai and Ha Giang provinces in the north, southwards to Kon Tum and Gia Lai provinces (Nguyen et al. 2009, Nemes et al. 2013. Elsewhere, the species has been reported from India, Bangladesh, China, Taiwan and Myanmar (Nguyen et al. 2009, Nemes et al. 2013).

Ecology
The voucher specimens were found between 19:00 and 22:30 h on forest paths. The surrounding habitat was secondary forest composed of medium and small hardwoods, lianes and shrub. Air temperature was 22-27°C and relative humidity was 75-85%.

Discussion
Amongst four survey sites in Son La Province, the snake species number recorded in Thuan Chau District was highest (47) In terms of conservation concern, Son La Province also harbours a high number of threatened snake species: 11 species listed in the Red Data Book of Vietnam (Dang et al. 2007