O . kikuzatoi through a series of field surveys as below. Current Herpetology 23(2): 73-80, December 2004 (c)2004 by The Herpetological Society of Japan Field Observations on a Highly Endangered Snake, Opisthotropis kikuzatoi (Squamata: Colubridae), Endemic to Kumejima Island, Japan HIDETOSHI OTA* Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Okinawa 903-0213, JAPAN Abstract: The Kikuzato's brook snake, Opisthotropis kikuzatoi, is a highly endangered aquatic or semiaquatic species endemic to Kumejima Island of the Okinawa Group, Ryukyu Archipelago. Field studies were carried out for some ecological aspects of this species by visiting its habitat almost every month from April 1996 to March 1997. The results demonstrate that the snake is active almost throughout the year. It is also suggested that the snake tends to be diurnal in the warmer season, and nocturnal in the cooler season. Observations on a case of autonomous emergence onto the land, very slow growth, and predation on small crabs, are also provided. Key words: Opisthotropis kikuzatoi, Field census; Activity pattern; Body temper- ature; Kumejima Island INTRODUCTION broadleaf evergreen forest: see below), led Environment Agency of Japan assign O. The Kikuzato's brook snake Opisthotropis kikuzatoi to the highest Red List Category kikuzatoi, is a small colubrid species endemic (IA) as one of the two most critically endan- to Kumejima Island of the Okinawa Group, gered reptiles of Japan (Matsui, 1991; Ota, Ryukyu Archipelago. Since its original 2000). This snake is also protected by laws of description by Okada and Takara (1958: as a both the National Government of Japan and member of the genus Liopeltis), no more than the Prefectural Government of Okinawa (Ota, ten individuals have been known to science 2000). (five preserved specimens and other five indi- To the present, very few ecological data, viduals examined and released: Toyama,1983; largely obtained through captive observations, Ota and Mori, 1985; OPBE, 1993). Such an are available for O. kikuzatoi (Ota and Mori, extremely limited distribution and rarity of 1985; Mori and Nakachi,1994: but see OPBE observations, along with apparent progression [1993] for a few field observations). Such a in the reduction and fragmentation of its puta- scarcity of field data obviously makes it diffi- tive habitat (i.e., running waters surrounded by cult to develop effective conservation mea- sures for this critically endangered species. Recently I obtained some ecological data for * Tel: +81-98-895-8937; Fax: +81-98-895-8966; E-mail address: [email protected] 74 Current Herpetol. 23(2) 2004 MATERIALS AND METHODS D611) equipped with glass sensor probe. Each snake captured was sexed by everting Of the ten individuals of Opisthotropis the hemipenes or by examining the external kikuzatoi hitherto reported, all but one were shape of the tail base, and then was subjected found under the water in streams and brooks to examination for snout-vent length (SVL), running on the floor of the evergreen broad- tail length (TL), body weight (BW), and ven- leaf forest (Toyama, 1983; Ota and Mori, tral (VT, sensu Dowling,1951) and subcaudal 1985; OPBE,1993). The other individual was counts (SC). Of these, SVL and TL were also found in a stream in the forest, but with measured to the nearest mm with a tape almost no surface water because of the measure, and BW to the nearest 0.1g with a summer drought (OPBE,1993). I thus fixed a portable electronic balance (Shimazu AXEWB- census course along a middle 350m portion of 35). Stomach contents were examined by pal- one brook, which was located on the border pation and forced regurgitation. For females, between the evergreen broadleaf forest on the oviductal eggs were also examined by palpa- mountain side and open grassy vegetation on tion. Finally the snake was individually marked the lowland side. by ventral clipping and released at the point During the period from April 1996 to March where it was captured. The whole process was 1997, I, together with one or two field assis- completed within 15 min so as not to exhaust tants, visited the site every month but October, the snake through handling. staying there for 24 hours (see Appendix 1 for Even while a captured snake was examined, further details). In each visit, census was the census was also continued as scheduled by carried out every hour from 0600 to 2000 and a field assistant. Animals other than O. every second hour from 2000 to 0600 by slowly kikuzatoi encountered during the census were (ca 10m/min) walking on the lowland side also recorded. along the stream, searching for the snakes both in the water and on the banks. For the RESULTS census at night, a flashlight was used as an aid. At the beginning of each census, water temper- Opisthotropis kikuzatoi was found 11 times ature (measured 10mm below the surface), air during the study period. Snakes were invari- temperature (measured in shade at 1m above ably active, moving on the bottom of the the ground), and water depth were measured stream, when they were first located. In a at a fixed standard point (henceforth referred finding in June, the snake successfully escaped to as SWT, SAT, and SWD, respectively). by suddenly emerging onto the forest side bank When a snake was found, its behavior was and quickly entering dense shrubbery. Of the continuously observed as long as possible. remaining ten findings in which snakes were However, when its escape into vegetation or captured for further examination (see above), other obstacles was likely, the snake was one in the early afternoon of 26 August and captured immediately. After capture, its body another after midnight of March 23 involved temperature (BT) was measured within 30 sec the same individual (Fig. 1). Snakes involved by inserting the sensor probe of an electronic in the remaining eight captures included no thermometer (thermistor) into the cloaca. Water recaptures. temperature (WT: 10mm below the surface) Of the nine individuals examined, four and air temperature (AT: in shade, 1m above (captured in July, August and March, Septem- the ground) were also measured at the point ber, and December) were males, and the where the snake was located at capture. All remaining five (April, July, September, Novem- temperature measurements (including SWT, ber, and December) were females. Data for SAT and SWD) were taken to the nearest quantitative external characters of these speci- 0.1 C using thermistor (Takara Digimulti mens were combined with data from previous OTA-FIELD OBSERVATIONS OF ENDANGERED SNAKE 75 FIG. 1. Times of day at which Opisthotropis kikuzatoi were found. Stippled area represents the extent of night (i. e., from sunset to the next sunrise) in each survey period (24h). The horizontal bar denotes dura- tion of observation of a given individual after its initial detection. Arrows indicate data from the same recap- tured individual. TABLE 1. Morphological characters (x±SD, followed by ranges in parentheses) of male and female Opisthotropis kikuzatoi. Data from the present and previous studies (i. e., Toyama, 1983; Ota and Mori, 1985; OPBE,1993) are incorporated. studies (Toyama, 1983; Ota and Mori, 1985; 31-75mm (Appendix 1), whereas WT, AT, OPBE, 1993) and were compared between and WD at capture (x±SD, followed by sexes (Table 1). In all these characters (SVL, ranges in parentheses) were 22.7±4.05 (16.4- TL, VT, and SC), no statistically significant 28.5)C,23.7±6.43(14.5-31.1)C, and 34.0± differences were recognized between males 29.73(11-105)mm, respectively. BT of the and females (ANOVA, P>0.05). SVL and BW snake at capture,24.7±5.21(16.4-29.2)C, of the recaptured male were, respectively, was significantly correlated with both WT 354mm and 9.2g at initial capture, and (r2=0.895, t=10.32, P<0.001) and AT (r2= 357mm and 9.1g at recapture, showing no 0.857, t=9.93, P<0.001). BT was almost discernible growth during the period of nearly consistently higher than WT, and also substan- seven months. tially exceeded AT when AT was equivalent to The time of day at which the snakes were or lower than 26.2 C. In contrast, BT was dis- found varied from 0200 to 1405. From April tinctly lower than AT when AT was 30.0 C or to August all snakes were found from late higher (Fig. 2). Regression lines for WT and morning to early afternoon, whereas all BT during the warmer (i.e., April-September) findings but one (for a female found at 0905 and cooler seasons (November-March: see of 24 November) were made between midnight Appendix 1), BT= 0.215*WT+22.98 (n=6, and sunrise during the period from September r2=0.60, t=2.44, P<0.05) and BT=1.397* to March (Fig. 1). WT-6.73 (n=4, r2= 0.98, t=9.48, P<0.05), SWT, SAT, and SWD in the present study respectively, significantly differed from each varied from 16.3-27.2 C, 12.7-32.0 C, and other in slope (ANCOVA: F=55.6, P<0.001), 76 Current Herpetol. 23(2) 2004 ing some more or less aquatic species (e.g., Mushinsky et al [1980], Shine and Lambeck [1985], and other papers cited in Gibbons and Semlitsch [1987]). Most such studies are about species in almost aseasonal tropics, or at much higher latitudes where low temperatures have crucial effects upon the winter activity of ecto- therms by forcing them into hibernation. In contrast, very little information is available regarding snakes in the subtropical regions (including the Ryukyu Archipelago), where seasonal climatic changes are prominent on the one hand, but winter temperature is not neces- sarily so low as to force ectotherms into hiber- nation on the other hand (e.g., Koba, 1962; Ota, 1994; Mori et al., 2002).