Research articles NAT. HIST. BUL L. SIAM Soc. 47: 129-147 ， 1999

THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ， SONGKHLA PROVINCE ，THAILAND

lohn C. Murph y1， Harold K. Voris 1， Daryl R. Karns 2， Tanya Chan-ara ，and Kopsak Suvunrat 4

ABSTRACT

百le ecology of the rainbow wa 旬rsn は.e ， Enhydris enhydris ，was studied ne 紅白 e village of of Ban Th a Hin on 白ee ぉ tsho 問。 fLake Songkhla ，in 1996 and 1997. Temperature ，humidity ， and and light were monitored. Snakes were 凶 pped ，injected with PIT tags ， and released. A to 凶 of of 235 individuals were marked and the population was estimated to range from 406 to 567. Snakes Snakes were also collected by hand in conjunction with a unique local fishing technique. Radioteleme 町 observations on eleven snakes demonstrated 血at they prefer 血e mud-root tangle tangle along 白巴 edges of the ditches and klongs. Body temperatures ranged from 29.2 to 32 .1・ C ， with no differences between the sexes. Radio transmitters were also implanted in

small small numbers of Enhydris plumbea ， Homalopsis buccata ， Xenochrophis piscator ，組 d Cylindrophis Cylindrophis ruffus. Observations were made on litter size ，diet ， and predation. An appendix lists lists all snake species encountered in the area.

問 TRODUC 百 ON

Lake Songkhla ，a 98 ，OOO-hectare wetland complex in southem Thailand ， is composed of three shallow basins. Th e lake has formed over 白e past 150 ye 紅 s as a series of barrier islands islands gradually enclosed the basins. The islands ，which now form the Sathing-Phra Peninsula ，almost completely isolate Lake Songkhla from the Gulf of Thailand; there is only one opening to 血e sea located at the south end of the lake ne 紅 the city of Song 凶 la. As a result of the changes in water levels and water chemis 町出at accompanied 白e formation of the lake ，Lake Songkhla has an unusual mixture of freshwater and marine flora flora and fauna. Wh en ANNANDALE (1916) reported on its fauna the lake was no more

I Depar 伽 lent of Zoology ，Division of Amphibians and Reptiles ，Field Museum of Natural History ，Lak e Shore Orive Orive at Roosevelt Road ，Chicago ，IL 60605 USA. 2 Department of Biology ， Hanover College ，H 組 over ， IN 47243 ・0108 US A. 3 Reference Collection Division ，National Science Museum ，Technothani ，Kh long 6，Kh long Luang ，Pathum- 出ani ，Thailand. Wildlife 4 Wildlife Technical Division ， Royal Fores 町 Department ，Phahoyo 白in Road ，Chatuchak ，Bangkok 10900 ， ailand. Th ailand.

Corr 官spondence to: Harold K. Voris ，Department ofZoology ，Di vision of Amphibians and Reptiles ，Fi 巴ldMuseum of of History Natural ，Lak 巴 Shore Drive at Roosevelt Road ，Chicago ，IL 60605 USA. FAX: 1・312-427 ・7269. E-mail: E-mail: hvoris@ 合nnh.org Received Received 15 October 1998; accepted 24 March 1999.

129 129 130 130 JOHN C. Mu 貯 HY ETA ム than than 4.9 m deep. Gradually the lake has continued to accumulate silt and today the three basins basins have a mean depth of 1.2 m and a maximum depth of 2 .4 m (LEELA W A THANAGOON ET A L.， 1997). The wetlands of Lake Songkhla are one of Thailand's unique and important natural resources resources and the lake is of regional significance as a stopover for many species of migratory birds. birds. A recent study of the fishes of Lake Songkhla (LHEKNIM ， 1998) demonstrates that the the basins of this lake and the nearby freshwater Thale Noi serve as a reservoir of marine and and freshwater species diversity. Thus ，it is not su 叩rising that this vast wetland complex provides provides an ideal location to study aquatic snakes. Lake Songkhla is home to perhaps the most diverse assemblage of aquatic snakes in the the world. One true sea snake (Hydrophis brooldi ，Hydrophiidae) ， one aquatic file snake (Acrochordus (Acrochordus granulatus ，Acrochordidae) ， one pipe snake (Cylindrophis rl{ 伊lS ，Uropeltidae) and and at least four species of Asian water snakes (Homalopsinae ，Colubridae) live in the lake or or along its wet edges. Our focus has been on the small- to medium-sized species of Asian water water snakes that are rarely more than one meter in total length. These snakes are characteriied characteriied by small dorsally oriented eyes ，crescent-shaped valvular nostrils ， enlarged rear rear fangs and mild venom. The 32 species of Homalopsinae are grouped into 10 genera and found westward to Pakistan's Pakistan's Indus Valley eastward to China and southward to New Guinea and Australia. The homalopsine snake Cerberus rynchops may be the most abundant snake on the plane t. For example ， as many as three dog faced water snakes occupies every meter of shoreline shoreline at the mouth of the Muar River in Malaysia (J A YNE ET AL ， 1988) and it appears to to occur in similar densities throughout much of its range from India to northem Australia. Half Half of the 32 species of homalopsine snakes inhabit the waters of Indochina and 8 of of these species are restricted to this region. Thailand has a particularly high diversity ， with with 12 species in its wetlands. This peak diversity suggests that this region is the likely center center of distribution and probable site of origin and evolutionary radiation for 出is group of of water snakes. While the anatomy ，taxonomy and overall geographic distribution of the Asian water snakes snakes has been studied at some length (e.g. ，SMITH ， 1943; GYI ， 1970; Mu 即 HY & VORIS ， 1994a) their natural history remains largely anecdotal (MURPHY & Vo 町 S， 1994b). Until Until recently the specifics of habitat use ， thermal biology ， food and feeding behavior ， reproductive reproductive cycles ， and population biology were virtually unknown. The ecology of Asian Asian water snakes is of particular interest because members of the subfamily are at different different stages of transition between terrestrial and aquatic life zones. For example ， the plumbeous water snake (Enhydris plumbea) is one of the more terrestrial of the group and although although it is usually found in paddy fields ，buffalo wallows ，marshes ，ditches ， and small streams ，it sometimes can be found on dry land several meters from standing water (KA. RNS ET A L.， 1996 and VORIS & KA. RNS ， 1996). On the other hand ， the keel-bellied water water snake (Bitia hydroides) may be the most aquatic as it rarely ，if ever ， leaves shallow or or intertidal marine habitats (JA YNE ，ET A L.， 1995). THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ，SONGKHLA 131

METHODS

Study Site

Th esωdy site (日 gure 1) is located about 0.2 km west of Ban Th a Hin ，at 血eB 姐 Tha Hin Royal Fores 住y Substation (7.23'N ，100.26'E) ， Thale Sap Non-hunting area ，on the southeast southeast side of Lake Songkhla's Thale Sap. The study site is approximately 20 ha. The major major habitat at the study site is extensive wet meadow dominated by a single species of grass ，Paspalum distichum L. (Gramineae) ，a salt-tolerant ， cosmopolitan species. At B 佃 Tha Hin P. distichum attains a height of from 0.5 to 0.75 m and is emergent in areas 白紙 紅 e continually inundated with water at lake level (Figure 2). Less common plants 血at occur occur at B 組 Tha Hin include Scirpus litoralis Schrad. (Cyperaceae) ， Najas marina L.， and Najas Najas minor All. (N 司adaceae). A narrow raised road runs west from Ban 百la Hin to 血e lake (Figure 1). Th e road is is closed to all vehicle traffic and is bordered by water-filled ditches on both sides 血at are are 1. 7 to 2.0 m deep ，1. 5 to 4.0 m wide ， and extend to the lake. Th ese ditches resulted from dredging during road construction and are deep enough to be f民e of emergent vegetatlon vegetatlon . 官 le northem edge of the study site is bordered by a canal (Klong 百la Hin) 白紙 runs west west from the town to the lake (Figure 1). The klong is approximately 25 to 40 m across and and attains a depth of about 0.7 m. Scattered mangroves (Sonneratia caseolaris L. Eng l.， Sonneratiaceae) Sonneratiaceae) occur along the edge of the klong and at 血e eastem perimeter of the study site. site. A smaller klong bisects 血e wet meadow south of the road and it intersects Kl ong Tha Hin at 出e west end of our study site (Figure 1). 官邸 minor klong is from 10 to 15 m wide ，and approximately 0.7 m deep. Several small canals (< 3 m width) branch off off of the minor klong and connect to the main ditches 血at parallel the road. A third canal ，Kl ong Huairut ， about 0.7 km south of the main study site was used for observations of of the puff-faced water snake (Homalopsis bucca ω). 官邸 canal 25 to 30 m wide ， is heavily heavily used by fisherman and it is bordered by Sonneratia c出 elo 紅 is 紅白s. Au 凶que anthropogenic feature of the canals 釘 'e teardrop-shaped fish bays dug into 由e bank of the canal (Figure 1). Many of these occur wi 血in and adjacent to the study site. 百le fish bays have a mean depth of 1. 4 ::!: 0 .3 m ，a mean leng 血 of 9 ::!: 0.9 m ，and a mean maximum width of 1. 8 ::!: 0.7 m. Th e fish bays are maintained by fisherman who place place tree branches in them ， and cover them with palm branches to provide shade. Both fish fish and snakes move in 叩 d out of 白e fish bays. Aft er several weeks fisherman seal off 白e narrow openings of bays with bo 紅 ds and mud ，pump out 血e water ，and collect 血e fish by hand.

Mapping

A grid sy 御 m composed of staked positions at 10m intervals was constructed during the the 1996 field season. The grid covered about 10 ，000 m 2 of 印刷dy area and was used to to map 血is portion of 血e sωdy site. Topographic and an 白ropogenic features (i. e. fish bays ，canals ，ditches ，buildings) were mapped and distances were calculated by 凶 angulation and and direct measurement (Figure 1). 132 132 JO H N C. MURPHY ET AL

W etM eadow

WetMeadow WetMeadow

e wat 巴r I 'J{_ ロ building I T -圃・ road I十

F igur e 1. A m ap of the st ud y sit e at Ban Tha Hi n. The w 巴t m ea do w is dom in ated by seas hore paspa lu m (Paspalum disti chum) . T he R oya l Forestry D 巴partment m an ages th 巴 Ba n Tha Hin area. A

口紅 row ro ad w ith dit ch es on both sid 巴S runs west from the vill ag 巴 (das h巴d line) . Two builclin gs on th es it e( rec tang l巴S on so u thern ed ge of road) se r ve as of fi ces for forestry per so nn 巴l

Fig U1巴 2. T he wet meadow at th e Ban Tha Hin s tudy sit e is domina tecl by the gra ss Paspalum disl ichu lfI A fi shenn ani ss how n w ith hi s boat and fi sh trap s in K long Tha Hin THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ，SONGKHLA 133

DATALOGGER LOCATiONS

べ→十

山 r .w W 巴tMeadow 口 building 25m 圃圃圃圃圃圃 road 「一一一一寸

Figure Figure 3. A map of th 巴 sa n Th a Hin st ucl ys it 巴 sho win g the loca tion s of th 巴 wea th er stations ancl mO SI of the th 巴rma lclata loggers

Environmental Monitoring

In In ord 巳r to describe th 巴巴nVlronm 巴ntal conditions availabl 巴 to the snakes at Ban Tha Hin we deploy 巴d 15 data logg 巴rs (Ons 巴tCO ll1 puter ，Procasset ，Massachusetts). Three data loggers loggers attached to as ll1 all weather station (1 m high) in th 巴 meadow (Figure 3) w 巴re us 巴d to to measure shaded air t巴mp 巴rature (T a) ，light inten si ty (lumens) ， and relative humidity (RH). (RH). A similar weather sta tion was loc at 巴d n巴ar a window in th 巴 forestry substation hou se . We deployed nine temperature data lo ggers in microhabitats available to th 巴 snake s. The data logg 巴rs wer 巴 pJac 巴d in sid 巴 copp 巴r snak 巴 mod els (copper tubes 2 cm in diameter ， 25 cm long; paint 巴d olive gr 巴en to match th 巴 l右目巴ctivity of the sn 心〈巴 s; and seaJed seaJed at both ends with stoppers) (PETERSON ET A L.， 1993). Th 巴 temp 巴ratur 巴 data loggers (T e models) recorded temperatur 巴 data 巴V巴ry 3 to 5 minutes from 18 July to 1 Augus t. A rain rain ga 時巴 adjacent to th 巴 small weather stat ion was checked daily The data logger s (T e ll1 odels) were placed in a broad rang 巴 of microhabitats in ord 巴r to to monitor the t巴mp 巴rature range at Ban Tha Hin. We paid spec ial attention to thos 巴 microhabitats microhabitats frequent 巴d by snakes. Figure 3 shows eight of 巴lev 巴n Jogger location s. -凶ム Table Table 1. Day any night statistics for centigrade temperatures for 11 locations and relative humidity for two locations at Ban Tha Hin as recorded by portable data loggers between July 17 and August 1， 1996. The number of readings is provided under the the measurements colurnn and the time between each measurement is provided in the interval column. Day readings were those those taken between 0600 and 1800 hours while night readings were those taken between from 1800 and 0600 hours. See the the text for more details on the position of the data loggers in the various microhabitats.

Measure- Interval Day Measurements Night Measurements Location Location ments ments (min.) 恥1ean Std. Min. Max. Mean Std. 民1in. Max. Meadow weather station 2182 5 32.44 3.64 23.03 38.14 26.53 1.3 0 24.06 32.39 Fores 町 substation 674 16 30 .4 8 2.72 25.21 36.00 27.89 1. 60 25.21 36.79

』 AδFish bay on klong 2017 5 30.96 1. 96 26.81 36.18 28.65 0.82 26.81 31.1 9 ozz C-5 C-5 Fish bay on klong 3154 3 3 1.1 9 2.08 25.36 38.58 28.75 1. 58 25.36 32.68 の・玄巴同司王句、 Deep in Klong Tha Hin 2017 5 3 1. 60 2.66 24.98 36.52 28.94 1. 54 25.15 33.05 K1 0ng root tangle 2176 5 30.90 2.08 27.55 35.82 29.95 1.1 3 27.55 33 .4 9 Deep in south ditch 2026 5 30 .4 4 0.62 28.98 31. 95 30.60 0.52 29.34 31. 58 F Ditch Ditch root tangle 2179 5 3 1.1 6 1. 48 27.89 34.23 30.69 1. 00 28.25 33 .4 6 Open exposed edge of ditch 2178 5 40.39 9.52 23.59 61. 87 25.96 1. 45 23.59 33.08 Open pool in meadow 2181 5 32.88 4.14 24.82 38.09 27.92 1. 83 24.82 33.9 Open root tangle in meadow 2180 5 32.05 4.11 24.39 38.16 27.20 1. 77 24.22 31.24 RH meadow weather station 675 16 68.85 15.58 41. 40 100.00 88.94 8.87 53.60 100.00

RH fores 住 y substation 674 16 69.08 13.36 4 1. 20 94 .4 0 80 .3 7 7.94 46.00 92.7 THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ，SONGKHLA 135

Along the edge of Klong Tha Hin we placed temperature loggers in the root-tangle of two fish fish bays (T A-5 日sh bay and Tc-5tlsh ti)at a depth 15cm (Table 1).In addition ，one logger was pl~ced o~~th~n ;:~d botto~ ~f" K'r~ng Tha Hin at a depth 70 c~ (T 刷 lQ 70 cm) and ano 出er was placed in the root 司 tangle of the south bank of the klong at a deptn 15 cm (T klong root- tangle) tangle) In In the south ditch one logger was placed on the mud bottom at a depth of 110 cm (Tditch (Tditch 110 cm) while another was placed 15 cm below the water surface in the root-tangle along along the edge of the ditch (Td; ，eh roo ，.， an.le)' A third logger was placed on the surface of exposed exposed mud on the south shore of kio 昭 Tha Hin (T 叫 osed mlρIn the meadow ，one logger logger was placed just 2 cm below th 巴 surface of the water in an open pool (T me 山 W 0001)' and another was placed in the root-tangle 15 cm below the surface of the meadow pool (T (T me"Q"w root-tangle Water teniperatures at different depths were measured in several aquatic habitats using thermal thermal probes (Table 2). Water temperatures in meadow pools were taken at the surface ， at at the bottom of the pool ，and at 5，10 ，15 ，and 20 cm below the bottom of the pool in the soft soft mud. Water temperatures were taken at the surface ，0.5 ，0.8 ，and 1. 0m below the

Table Table 2. Mean and standard deviation of water temperature (C) at different depths in several several habitats at the Ban Tha Hin study site.

Temperature Temperature (C) Mean Habitat Habitat Depth (m) 0700 hrs. 1600 hrs. Difference Klong Surface 27.6+0.0 32.9+0.1 5.3 0.50 0.50 m 27.6+0.1 33 .1 +0.1 5.5 0.80 0.80 m 27.5+0.0 33.1-0.1 5.6 1.00 1.00 m 29 .4 +0.3 31.0+0.3 1. 6 Fish Fish bay Surface 28.3+0 .4 31.6+0.5 3.3 0.50 0.50 m 28.2+0.5 31. 4+0.3 3.2 0.80 0.80 m 28.1 +0.3 30.9+0.5 2.8 1. 00 m 29.5+0.1 29.7+0.1 0.2 Meadow Surface 25.1+0.2 33.5+ 1. 0 8 .4 0.02 0.02 m 25.1 +0.3 33.0+ 1.7 7.9 0.07 0.07 m 25.9+0.5 32.2+0.9 6.2 0.12 0.12 m 28.2+0 .4 29.9+ 1.1 1.1 0.17 0.17 m 28.0+0.3 30.2+1.2 2.2 0.22 0.22 m 27.0+0 .4 31.1+1. 0 4.1 Ditch Ditch Surface 30.0+0.1 3 1. 9+0.1 1. 9 0.25 0.25 m 30.1+0.1 32.0+0.1 2.0 0.50 0.50 m 30.1+0 .1 32.0+0.2 1. 9 0.80 0.80 m 30.1+0.1 31.6+0.1 1. 5 1.00 1.00 m 30.0+0.1 31 .4 +0.3 1. 4 136 136 JOHN C. MURPHY ET AL water's water's surface in the klong ， in fish bays ， and in the ditches. The temperatures were tak: en in in the moming (approximately 0700 h) and the aftemoon (approximately 1600 h). The salinity and pH of the water was measured using Hach Colorimetric Test Ki t and litmus litmus paper respectively. The measurements were taken in the south ditch ，fish bays ，出 e klong ，and meadow pools. The pH of all of sites was circumneutral (6. 6-6 .9 :1:0 .1) based upon three tests taken at each location. The salinity of the meadow pools (6.5 :1:0.3 ppt) was approximately twice 出at of the water in the south ditch ， the klong ，and the fish bays (3.3-3.5 :1:0.4 ppt).

Trapping

The study site was visited from 17 June to 12 August 1996 ，and from 21 June to 8 July July 1997. Funnel traps were constructed from aluminum window screen and plastic screen. 百le traps had a funnel diameter of 25 cm and a leng 白 of about 60 cm. 百le funnel openings openings into 血e 住aps were about 4 cm in diameter and a 15 cm long ，f1 0ppy nozzle of plastic plastic screen was secured to 血e funnel opening inside the 住ap. In 1996 we deployed 18 回 ps in ditches and canals for 12 days ， 36 traps along the lake shore for 12 days ， and 25 住aps in meadow pools for 10 days. Traps were baited with small pieces of fresh fish. Each day all the traps were checked and each snake was weighed to 血e nearest 0.1 g， snout to to leng vent 出 (SVL) measured to 血 e nearest mm ， and subcaudal scales counted to determine sex. sex. Snakes were then released in 出 e vicinity of where they were trapped. In In 1997 ， 51 traps were deployed along the south edge of Klong Th a Hin and in ditches (Figure (Figure 4) for 13 days. An additional 16 住aps were deployed among these traps for the last last four 仕ap-days. For pu 中 oses of analysis we calculated the number of trap-days as 出e cumulative cumulative total number of days of trapping. The rate trap was calculated as the total number of snakes trapped divided by the respective number of trap-days. We divided the study study site into four trapping regions: the klong ， east ditch ， west ditch ，and south ditch (F igure 4). Each snake caught in 1997 was placed in a plastic bag with its 回 p number ， and weighed weighed to the nearest 0.1 g. Snout-vent and taillength measured to the nearest mm ， and subcaudal subcaudal scales were counted to determine sex. Pri or to release at 血e site of cap 旬re a passive passive integrated transponder (PIT) tag was i吋ected subcutaneously.

Radiotelemetry Radiotelemetry

In In the two ye 紅 s of the study ，temperature-sensitive radio 仕組srnitters (Holohil Systems ， Co 中， Ontario ， Canada; Model BD-2; size 4x8x15 mm ，1. 8 g; Model SI-2T ，5xl0x20 mm; 9.1 9.1 g battery ， battery life four weeks at 30 ・C; range <200 m) were implanted intraperitoneally intraperitoneally into 11 Enhydris enhydris (2 males and 5 females in 1996 and 4 males in in 1997) ，2 female E. plumbea in 1996 ， and 1 female Homalopsis buccata in 1996. Transrnitters Transrnitters were also implanted in 1 red-tailed pipe snake (Cylindrophis ruffus ，Uropeltidae) and 1 common keelback (Xenochrophis piscator ，Colubridae: Natricinae) in 1997. 百le surgical surgical procedures of KINGSBURY (1 994) and REINHARDT & CUNDALL (1982) were followed. followed. Transrnitters were calibrated in wa 旬rba 伽 before and after use and performed within within OSC. Body masses for the E. enhydris ranged from 57.0 to 125.0 g， for E. THE ECOLOGY OF THE W ATER SNAKES OF BAN TH A H IN ，SONGKHLA 1 37

蹴 r .w W 巴tMeadow 口山 25m 圃圃圃圃圃圃 road li「一一一一一 l

Figllre Figllre 4 . A l1l ap of th 巴 Ban Tha Hin sllld ys ires ho w in g lh e locat ions and nll mber s of lrap s in fOllr ar eas; klong ，巴as tdit ch，weS l dirch and so ulh dilCh. NOle lh e fi sh ba ys loca teda long lh e sO llth s hore of th 巴 ong. klong.

plumbea masses were 7 1 and 146 g，a nd for th 巴 H. buc c ata the ll1 ass was 265 g. Trans ll1 itt ers did did not exceed 3.5 % of the snakes body mass in any cas 巴 Fur th 巴r deta il s ll1 ay b巴 fo und in in KARNS ，E T A L. (in pr 巴pa rat ion).

RESUL TS AND DISCUSSION

Local Local Climate

The we t me adow at Ban Tha Hin is 出e dominant hab itat and it ex hibit s lar ge daily flu ctuations in li g ht int ensit y， a ir t巴Il1 perat Lll 巴 (Fig ur e 5) a nd r巴lative hU ll1 idity (F i gure 6). Data l ogger ll1 e asurements from th 巴ll1 eadow weat h巴r stat lon ov 巴ra3 -day p巴riod in July show hot dry d ays alt 巴rnating wit h warm hU l11 id night s. Air t巴mp 巴ratures grad uall y d巴cr巴ased through through th 巴 ni ght to [巴 ach lows in the ea rl y morning wh .i le I巴lat iv 巴 humidit y in cr・ease d throu gh the ni g ht to oft 巴n reac h 100 % b巴for 巴 sunns 巴 (Figur 巴 6). Ai r temp erat ur es increas 巴d 138 138 JO H N C. M U R PH Y ET A L.

40 1000

「一 (O) 800 Q 35 工↓一 凶庄コト〈江凶 z 600 mZω↓ 30 nLE 400 一↓〈(亡

凶ト 25 ω 200 『)

20 Lll.W ・...... ~ ! !!! ! ! ! ! !!! ! さとと士士士士..よ.~ !!!!! ! !! ! !! ! ~土土士士土土土士とと ~ O 0000000000000000000000000 。666666000000000000000000 N 凹∞ .....0 の CD O>C\J LO ∞ .....0 の CD O>C\J凶∞ ~O の CD O>C\J ~~~N ~~~N ~~~N ~

TIME (1 ・hour intervals - July 19-22 ，1996)

FigUJ 巴 5 Th 巴 relatio nship b巴tw een air temp e rature ancl li g ht ove r a thr ee clay periocl (J ul y 19 to 22 ，1 996) at th e wea th 巴r slat ion l ocatecl in th e m e aclow b巴tw ee n K long Tha Hin ancl th 巴 roacl (see figure 3) . No t巴

that that th 巴 mr temp 巴ratul 巴 (Tmcado lV a) usuall y lag s b巴hin cl the m eaclow li ght int 巴nSlty as m 巴as ur 巴cl in IU11l en s p巴r sq uaJ巴 foot

40 100

刃m (O) 「〉↓一〈同工 35 80 凶広コト〈江凶止豆凶ト

C 30 60 三一口一↓〈(ポ)

25 40

NIGHT N IGHT NIGHT 国置函盤盤極圏 臨盛留置留趨薗 臨麗麗密留置蜜 20 111 1 11111111 1 1111 ↑11 1 1111111111111111111111 1 11111111111111 ハリハ川↑ 1111 120 0000000000000000000000000 0000000000000000000000000 N 凶∞ .....0 の CD O>C¥J ω∞ .....0 的 CD O>C¥J凶∞ .....0 の CD O>C¥J ~~~N ~~~N ~~~N ~

TIME (1 ・hour intervals - July 19-22 ，1996)

Figur e6 The relat ions hip betw een the ai rt em pe rat ur e ancl re lati ve hU 11l iclit y ov er a 3- cl ay pe ri ocl at Ban Tha Hin .As air t巴11l peratur es rose af ter sunri se ，lh 巴 rel日tl v巴 hUllliclit y cl 巴clin ecl; as th e te11l peratur es clropp ecl

fo ll ow in gs un s巴t the hUllliclit y r ose THE ECOLOGY OF THE W ATER SNAKES OF BAN THA HIN ，SONGKHLA 139

through through the morning to reach highs betw 田 n 1200 組 d 1500 hrs wh i1 e relative humidity reached reached lows ne 紅 50% during 血is same period. Table Table 1 gives the means ，standard deviations and ranges of temperatures recorded by data data loggers over 14 days at the meadow weather station ， at the forestry substation weather station ， and in nine microhabitats ava i1 able to snakes. Ai r temperatures at the meadow weather weather station ranged from 23.0 to 38.1 DC during the day with a narrower range of 24.1 to to 32 .4 DC during the nigh t. The most extreme temperatures were found on the exposed mud bank where the temperature reached a high of 61. 9DC during the day and a low of 23.6 ・C at night. The exposed mud bank also exhibited the highest mean day-time temperature temperature (40 .4 0 C) and the lowest mean night-time temperature (26.0 ・c) of any of 白e microhabitats microhabitats monitored. The mean day-time and night-time temperatures of the fish bays ， the klong and the ditch are remarkably sim i1 ar at 30 to 32 0 C during the day and 28 to to 31 0 C during the nigh t. The mean temperatures in the meadow were about 1 DC warmer during during the day and about 10 C cooler at night than the mean temperatures in the fish bays ， 出e klong and the ditch. None of the primary aquatic habitats showed substantial vertical temperature stratification stratification (Table 2). Water temperature differences between early moming and early evening evening were greatest in the shallow meadow pools.

Habitat Habitat Utilization

Traps Traps placed in pools within the wet meadow produced a few snakes. The great m 吋ority of E. enhydris (n=229) came from traps set along the edges of the klong ，出 e fish bays bays and the ditches. Radiotelemetric tracking of 11 E. enhydris (5 females ，6 males) revealed 血at although 血is snake will occasionally venture into pools and small narrow ditches ditches of the wet meadow ， the bulk of its activity appe 釘 s to be restricted to the root- tangle tangle habitat at the aquatic-edges of the klong ， the fish bays and the ditches dissecting the wet wet meadow. This water snake spends most of its life within a1 m wide band along the margins margins of open water. This finding is consistent with the view of CAMPDEN-MAIN (1970:75) (1970:75) who wrote that it is “… entirely aquatic..." (see also MURTHY ， 1987:11 and WALL ，1912:1019). E. E. plumbea and Homalopsis buccata were trapped in small numbers during both years but 血ey too appe 紅白use the root-tangle at the edges of the klongs and ditches. Cylindrophis rl{ がIS also was similar to E. enhydris in its use of the aquatic-edge microhabita t. However ， radiotelemetry radiotelemetry data suggests 出at 由is species may be more sedentary ，staying within a few squ 紅 'e meters over an 8-d ay observation period. Radiotelemetry and direct observations demonstrated demonstrated that 血e common keel back snake readily moves ove r1 and through open meadow ， as well as in and out of meadow pools and ditches at the study site.

Snake Body Temperatures

Di umal snake body temperature (T b) data from 11 E. enhydris (6 males and 5 females) were were obtained using radiotelemetry in 1996 and 1997 (KARNS ET AL ， in preparation). No differences differences were found between the body temperatures of male and female snakes (males 支=30.2 0 C ，females 孟=30 .5"C). Snake body temperatures proved to be relatively stable 140 JOHN C. MURPHY ET AL.

E. enhydris (11) I / fishbay I ditch root-tangle (fJ I z I 0 klong root-tangle d ~ I I g meadow root-tangle I _J ~ deep klong (70cm) - 0 I :2: deep ditch (11 Ocm) ~ ~ \ exposed mud bank -

\ a1r - I,. 'I ~~1r~~~~~~~~~~~~~~~~~~~I 20 25 30 35 40 45 50 55 60 65 ENVIRONMENTAL TEMPERATURE (C) (JULY 18- AUGUST 1, 1996)

Figure 7. The mean and range of environmental temperatures in 7 microhabitats at Ban Tha Hin, as compared to the mean body temperature of 11 Enhydris enhydris (5 females and 6 males) . Note the similarities between the snake' s mean body temperature and the mean temperatures in the aquatic microhabitats.

and ranged from 29.2 to 32.1 OC (x = 30.4°C, sd = 0.86, n = 110). Figure 7 shows the mean and range of body temperatures of the 11 rainbow water snakes relative to the mean and range of temperatures in the various microhabitats. Note that the average snake body temperature is similar to the average temperatures observed in the klong, the klong root­ tangle, the ditch and the ditch root-tangle. Figure 8 shows diurnal and nocturnal body temperatures for 5 telemetered E. enhydris followed closely for 3 days and nights in 1996. The snake body temperatures fall within the minimum and maximums of the temperature loggers most of the time and show little variation from 30°C. Thus, the rainbow water snake appears to be a thermoconformer. Data for two other species of homalopsine water snake found in the wet meadow were obtained using radiotelemetry (Figure 9). Two female E. plumbea had body temperatures that ranged from 28.6 to 30.1°C (x = 29.4, sd = 1.1, n = 28) and one female H. buccata exhibited body temperatures ranging from 28 to 32oC (x = 30.1 °C, sd = 1.2, n = 10). Two other semiaquatic snakes were monitored in the wet meadow during the day in 1997. One male C. ruffus had body temperatures ranging from 29.5 to 31.1 OC (x = 30.1 °C, sd = 0.5, n = 8) and one male X. piscator had a range in body temperature from 26 to 28SC (x = 27.5, sd = 1.0, n = 8). The data summarized in figure 9 suggest that the three species of homalopsine water snakes and C. ruffus are all thermoconformers, showing body temperatures of 29.3 to 30.3°C, similar to their immediate surroundings. However, the diurnal, actively foraging X. piscator showed a lower mean body temperature (27SC). This is unexpectedly low, considering we observed it foraging for frogs in the midday heat. It seems probable that it is able to achieve these relatively low body temperatures by evaporative cooling as it THE ECOLOGY OF THE WATER SNAKES OF BAN THA HI N ，SONGKHLA 141

- E.e .208 -E .e.230 -E .e.248 -E .e.271 TEMPERATURE (C ) E.e.290 ーT min - T ma x 60 Enhydris enhydris (N=5) 55

50 -~ 45

40 35 -1

30

25 寸-

20 ...L 。。。ももももも。>:l むむ .CY 心心 .CY 心心むむむむおむも心心むむむ~CI ~CI ~CI ~CI ~CI 。うう勺勺勺勺もももむ むむ .CY む やや・ゃ"ず・ 0 ーもーもも，，'V ，，':i'"，，'O'"，ずももももやふや φ0・もももーやー

TIME (July 19-22 ，1996)

Figur e 8. T he Iherm aJ rang 巴 al Ban Tha Hin. Max imum temp eratu r es ar巴 show n by th et hi ck grey lin 巴， 011111- mum lemp 巴ratur es by th 巴 thi ck bl ack lin e. Th e5 thin ，b l ack lin es ar 巴 th 巴 body temp erat ur es of 5

ind ividual Enhydr is enh ydris ，w hi ch m aint ain a n制 row thenn al pr efe ren ce by th巴rmall y co nf ormin g to the we t mud roo t-tangle mic rohab it at

E. E. enhydris (6 m) 1- E. E. enhydris (5 f) 1- + E. E. plumbea (2 f) 1-

H . buccata (1 f) 1-

Cylindrophis (1 m) 1- 咋→ Xenochrophis (1 m) ←~

mud-root-tangle 1

20 25 30 35 SNAKE BODYTEMPERATURE (C)

Figllr e9 . Th e m ea n and ran ge in body tempe ratllr e for 5 spec ies of sn akes fOll nd at Ba n T ha Hin. Th 巴 nllmb 巴l of of indi vidll als and lh eir sex (m = m ale，f = [，巴 ma le) is giv巴n 1n p釦 enlhe ses . NOI 巴 lhe 3 hom alops in es

(Enhyd ri s enh yd ri s， E. plwnb ea ，a n d /-1. buccara) a nd Cyl ind roph is ru .ff us h ave simil ar mean t巴mpe ra- tur es of a bout 30・C. Xellochrophis pisca/or h ad the lowest m 巴an body temp 巴ratur e. A lth oll gh ac ti ve durin g th 巴 heat of midday ，it m aint ain sa low erb ody temp eratllr 巴 by evapo rativ e coo lin g 142 142 JOHN C. MURPHY ET Aι moves in and out of meadow pools during the midday conditions of high temperatures and relatively relatively low humidity.

Population Population Size and Density

τ'h ere was little visual evidence for the presence of snakes at the study site.τ 'h e turbid wa 旬:r and dense vegetation combined wi 白白.e cryptic coloration and behavior of 血is snake snake render it all but invisible. Snakes were occasionally se 四 at night ，and one of us saw a snake quickly surface and then dive at midday. 百lese few sightings over hundreds of hours hours of field work were quite misleading as to the actual number of snakes present at 出e study study site. E. E. enhydris was 由e most abundant snake in the funnel 回 ps ， with a total of 235 snakes receiving receiving PIT tags. A total of 380 E. enhydris were capωred and recap 旬res numbered 144. 百le details of the E. enhydris population size estimates will be published elsewhere ， but but prelimin 紅 y results suggest that between 406 and 567 E. enhydris were present at 血e S制dy site. 百le density of snakes along the edges of the ditches and klong was approximately 1 snake per 2 meters of shore line.

Size Size Di stribution

Neonates Neonates of E. enhydris have a mean SVL of 155 mm (1 43 to 162 mm ， n=15) based upon our measurements of specimens bom to two females obtained in 血e Bangkok marke t.百世 s is almost twice 白e size of 白e young reported by BATCHELOR (1 958:109) ， who stated neonates were about 3 inches. Th e smallest snake we found at 白e study site had a SVL of 300 mm ，and all others (n = 251) fell into 出e 350 to 549 mm SVL classes. Th e absence of young snakes in 0 町田ps may be because the young snakes may use di 町erent microhabitats and 由ey may forage differently.

Neonates Neonates of E. plumbea 紅 'e poorly known. Th e smallest museum specimen we measured was 135 mm in SV L. In Bomeo a freshly caught female with a pre-p 紅佐uition mass of 39.5 39.5 g gave birth to five young that had an average SVL of 127.2 mm (r 叩 ge 126 to 130 mm). Th e five young had a combined mass of 10.5 g (VO Rl S & KARNS ， 1996). Four E. E. plumbea collected at Ban Th a Hin in 1996 ranged in size from 370 to 530 mm SVL. Five Five collected in traps in 1997 were from 36 4- 563 mm SV L. Eighteen Eighteen near full term embryos from a female H. bucatta collected at 也e study site were 115 to 216 mm SVL (mean ，202 mm). Nine adult H. bucatta collected in 1996 佃 d 2 in 1997 ranged in SVL from 422 to 810 mm. LIM & LEE (1 989) state that hatchlings of X. piscator 紅 e about 110 mm. Two specimens collected collected in 1996 ， and 3 in 1997 ， ranged in SVL 仕om 306 to 577 mm. 百le snake measuring 306 mm in SVL was likely a subadult while the others were adults. LIM & LEE (1989) reported reported the young of C. rZ{ がIS with SVL of 205 mm at hatching. Two specimens collected collected in 回 ps at Ban 官la Hin in 1996 had SV lengths of 282 and 460 mm.

Sex Ratios

Our data on 血e sex ratio of E. enhydris at Ban Tha Hin 紅 'e highly variable. For THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ，SONGKHLA 143

example ， of 66 E. enhydris trapped in the south ditch in 1997 ，54 were males and 12 were females females (sex ratio 4.5 males per female). On the opposite side of the road in the west ditch ，39 males and 16 females were tapped (ratio 2 .4 :1). The total ratio of E. enhydris in in 1997 was 3.1: 1. We suspect that this skewed sex ratio may be due to behavioral differences differences between males and females. For example ，many females are gravid in June- July July when the field work was carried out ，and hence they may not have sought the food offered offered as bai t. This hypothesis is suppo 巾 d by the that fact gravid snakes of several t邸 a will 仕equently re 白 se food in captivity ，and females found with embryos in advanced stages stages of development rarely contain food (see SHlNE ，1988 ， for a review). Of six

E. E. enhydris that were hand caught in drained fish bays in 1997 two we 陀 males and four were females ，which further supports the idea of an even sex ratio.

Reproduction

Wh at little is known about the reproductive behavior of E. enhydris is anecdota l. WALL (1912:1019) wrote “.. .Evans came across a pair ‘incopula' at Hmawbi (Lower Burma) on 16th October 1899..." Other authors (ACHAR lI & MUKHERJEE ， 1966:79; KOPSTEIN ， 1930:307; POPE ， 1935:135; TAYLOR ， 1965:914) have reported parturition in all months between March and Augus t. Gravid female snakes obtained in a Bangkok market in in June and July gave birth in both ofthose months. Cox (1 991) summarized the literature on clutch size and reported litters of 6 to 18 young. While handling snakes for data collection we frequently had male snakes vibrating their their body in our hands and assumed this behavior to be a response to female phermones left left on our skin from previously handled females. In In 1996 and 1997 ，34 female E. enhydris from Ban Tha Hin were exarnined for reproductive reproductive status. Seventeen of 22 (57%) contained eggs or embryos (mean number = 7.9 ， range = 5 to 16) in the 1996 sample ，and 5 of 12 (42%) contained eggs or embryos (mean number = 6.4， range = 4 to 7) from the 1997 sample. The number of eggs and embryos was positively correlated with female body size. The smallest gravid female was 38.5 38.5 cm SVL ， the largest was 52.9 cm SV L. ST. ST. GIRONS (1972) and BERRY & LIM (1967) considered H. buccata to breed year round ，al 白ough the later authors believed breeding peaked between October and March. Li tter sizes reported in the literature ranged from 4 to 21 young (BERGMAN ， 1951; SMITH ， 1943). BERGMAN (1951) reported on 11 litters that ranged in size from 4 to 17 young with a mean of 10. An 81 cm female H. buccat αfrom， Ban Tha Hin in 1996 contained contained a litter of 18 young. We collected no data on reproduction from E. plumbea ， C. C. rゆ s， or X. piscator at the study site.

Di et

E. E. enhydris appears to feed exclusively on fish at Ban Tha Hin. Animals taken from traps traps had frequently eaten the bait (pieces of dead fish). Th e draining of fish bays provided an an opportunity to watch snakes capturing and trying to eat stranded fish and in these instances instances snakes frequently took fish larger than they could swallow. In one instance a snake snake seized a stranded three-spot gourami ，Trichogaster trichopterus (Belontiidae) ，by the 144 144 JOHN C. MURPHY EI' AL head ， picked the fish up in its jaws ，and with the first third of its body off the mud substrate moved about 1. 5 m ， probably in search of a secure location to swallow the fish. T. trichopterus trichopterus were taken from the stomachs of five specimens from the fish bays ，and a sixth sixth specimen contained unidentified fish remains. Three species of fish Channa striatus (Channidae) ，Trichopsis vittatus (Belontiidae) ， and Trichogaster trichopterus) frequently entered entered the 回 ps 加 d may have attracted snakes. Others (ACHA 即 I&MuK 田町EE ，1966:79; CAMPDEN-MAIN ， 1970:75; SMITH ， 1914:100; SMITH ， 1943:384; TAYLOR & ELBEL ， 1958:1159; 1958:1159; TAYLOR ， 1965:914) have also considered E. enhydris to be piscivorous. We collected no data on the food habits of E. plumbea at Ban τ'h a Hin ， but other populations populations feed on frogs ，tadpoles ， and fish. VORIS & KARNS (1 996) showed that a population population of this species in Bomeo has a preference for larval amphibians. Of the five specimens of H. buccata from Ban Tha Hin 白at we exarnined ，one contained contained one fish ，Anabas testudineus (An ab 叩 tidae).τ 'h e literaωre on this species suggests that that it feeds on amphibians ，their larvae ， and fish (FRITH ， 1977 and SMITH ， 1943) C. C. rl{が lS feeds on other snakes (Tw EEDIE ， 1983) and eels (Cox ，ET A L.， 1998) and our observations observations suggest 出at it feeds on E. enhydris at B 叩 Tha Hin. X. piscator feeds on frogs frogs and we observed 血is species foraging actively on Rana erythrea at the study site.

Predators Predators

The secretive nature of snakes makes direct observations of predation difficul t. Nevertheless ，we observed many potential snake predators at Ban Tha Hin. Local fishermen fishermen caught a small-clawed otter ，Aonyx cinerea (Mustelidae) on the study site and these small carnivores 訂 'e likely to prey upon any appropriate sized vertebrate 出ey encounter. encounter. Herons ， Casmarodius albus ， Egretta garzetta (Ar deidae) and Bubulcus ibis (Threskiornithidae) (Threskiornithidae) were seen wading at 白em 訂 gins of the klong and roadside ditches daily ，and 紅 e likely predators on snakes. Additionally ， the eagle ，Hatiaeetus leucogaster (Accipitridae) (Accipitridae) was observed near 出e site ， and is known to feed on aquatic snakes. Other Other snake species feed on homalopsines ，at 出 is site. In 1996 a trapped pipe snake (c. (c. rl{仰 s) regurgitated two E. enhydris. We did not observe Xenopeltis unicolor (Xenopeltidae) (Xenopeltidae) at the study site ， but a road-killed specimen was found nearby. Wh en we presented presented a captive X. unicolor with a neonate E. enhydris ，it ate it. Two Bungarus fasciatus fasciatus (Elapidae) were taken from 住aps at B 組 Tha Hin ，and MAO (1970) reported this snake snake to feed on E. plumbea. The cobra ，Naja kaouthia (Elapidae) was observed near Ban Tha Hin. This snake is well known for its snake-eating habits and it most likely feeds on homalopsines homalopsines at 出is site (WALL ， 1913). Large Large fish at Ban Th a Hin may also pose a 也氏at to small snakes at Ban Tha Hin. Five Five species of catfish ， Arius caelatus ， A. maculatus (Ariidae) ， Clarias macrocephalus ， C. C. nieuhofii (Cl ぽ iidae) ，Ompok bimaculatus (Siluridae); and two species of snakeheads Channa lucius ， C. striatus (Channidae) 紅 e alllikely predators of juvenile snakes. aquatic

Summary

Within Within the wetlands at Ban Tha Hin ， the rainbow water snake ， E. enhydris ， occurs in high high densities in the mud root-tangle along the edges of the klongs and ditches. Several THE ECOLOGY OF THE WATER SNAKES OF BAN THA HIN ，SONGKHLA 145

other other snake species use 血 is microhabitat but do not attain high population densities. The body temperature of E. enhydris remains close to 30 ・C and conforms closely to 出e temperaωre of its preferred microhabitat ， the mud root-tangle. This is in contrast to Xenochrophis piscator which uses multiple microhabitats and cools its body during the day by by evaporation. E. enhydris forages for fish bo 由 at night and during the day in meadow pools pools and along the edges of ditches and klongs that dissect the wet meadow.τ 'hi s is in contrast contrast to snakes such as Cylindrophis rl{ がIS ， which are extremely sedentary and others like like X. piscator 出at forage between te 紅白出al and aquatic microhabitats. Male E. enhydris entered entered our funnel 住aps 3 times more often th 姐 females ， but the sex ratio of snakes hand- collected collected 合'O m fish bays was nearly 1 to 1. Information from the literature on reproduc- tion ，diet and predators of E. enhydris is pr ，回 ented to complete an overview of the ecology of of the rainbow water snake.

ACKNOWLEDGMENTS

We wish to th 創 tk 血e Biology Dep 紅佃lent of the Pri nce Songhkla University for its sponsorship sponsorship and warm hospitality. We 由ank Pitiwong Tantichodok ， Vachira Lhela 世m ， and and Pimonpan Leelawathanagoon as well as other faculty for their help and cooperation. We also 白創tk Udumsak Darumas for his generous help with local 仕'anspo 坑ation. At the study study site Mr. Pradup made snake collecting possible. We 白ank Jack and Raynoo Cox for for their hospitality in Bangkok. Sponsorship for this work was generously provided by Schwann Tanhikom ，Director of the Wildlife Research Di vision of the 百凶Royal Fores 町 Dep 副 ment ，Jarujin Nabhitabhata of the National Scien 回 Museum ， Somchai Bussarawit of of the Phuket Marine Biological Center ， Pitiwong Tantichodok of 血e Prince of Songkla University University and Mrs. Tuenchai Niyamangko of the National Research Council of Th ailand. At the Field Museum much appreciated assistance with 血is research came from C. Simpson ， T. T. Anton ， A. Resetar ， C. Redhed ，1. Fauci ，M. Brown ， and S. Murphy. We also are grateful to to the Field Museum of Natural History and Hanover College for financial support of 血is research. research.

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Appendix Appendix 1. A prelimin 紅 y checklist of the snakes from Ban Tha Hin and surrounding areas ， Songkhla Province ，Thailand. Whi le we moved to and 企om 出e study site we salvaged salvaged road killed snakes (DOR) ， and made notes on other snakes observed in ne 紅 by habitats. habitats. One of 血e most productive habitats was 血e dry paddy 佃 d sug 紅 palms 血at bordered bordered the 5 km road connecting Route 408 to Ban Th a Hi n.

Acrochordus Acrochordus granulatus (in lake ，collected with seine); Chrysopelea omata (n=1 DOR); Cylindrophis Cylindrophis rl.{ 酔IS (n=3 in traps); Dendrelaphis caudolineatus (n=3 DOR); Elaphe radiata (n=2 (n=2 DOR); Enhydris enhydris (n=5 DOR ， most abundant snake in aquatic 住aps); Enhydris plumbea (n=9 ， in traps); Homalopsis buccata (n=3 in traps); pη， as korros (n=1 DOR); Xenochrophis Xenochrophis piscator (n=7 DOR ，叩d in traps); Xenopeltis unicolor (n=2 DOR); Bungarus fasciatus fasciatus (n=3 in 回.p， and in gill nets in ditch); Hydrophis brookii (n=6 in lake ，collected with with seine); Naja kaouthia (n =4 DOR).