J. Mamm. Soc. Japan 19 (1) : 21-32 June 1994 Habitat Use and Selection of the Siberian Weasel Mustela sibirica coreana during the Non-mating Season Hiroshi SASAKI* and Yuiti ONO** Laboratory of Ecology, Department of Biology, Faculty of Science, Kyushu University, 33, Fukuoka 812, Japan *Present address : Chikushi Jogakuen Junior College, Ishizaka, Daznifu, Fukuoka 818-01, Japan * *Emeritus professor (Accepted 10 December 1993) Abstract. Habitat use and selection of the Siberian weasel Mustela sibirica during the non-mating season were studied, on the small island of Aoshima, Japan, from 1982 to 1989. Weasels occurred throughout the island. The village area was compared with the northern grassland which was less affected by human activity. Weasels in the village area were divided into two groups ; the "border weasels", which had their ranges around the periphery of the village, and the "central weasels", which occupied the center of the village. The population density was lower in the grassland area than in the village. The body weight of border weasels was the largest on Aoshima. Border weasels rested in barns and houses and were active in grasslands and on roads, while weasels in the grassland rested and were active mainly in grasslands. Weasels frequently used piles of hay in barns as resting sites in the village. Resting sites, offering good thermal conditions, are thought to be important factors of the range of the Siberian weasel, especially for females, during winter. The village periphery was assumed to be the most favorable weasel habitat because the village area provided good resting sites and a wide range of food. Key words : Siberian weasel ; Habitat use ; Home range ; Resting site The spacing pattern and social organization of mustelids have been discussed by several authors (Lockie 1966, King 1975, Powell 1979, Erlinge 1977a, Birks and Linn 1982). Least weasels Mustela nivalis and American mink M. vison are thought to have intrasexual territories (King 1975, Gerell 1970, Birks and Linn 1982). Erlinge and Sandell (1986) reported that male stoats M. erminea have intrasexual territories during the non-breeding season, and are non-territorial during the mating season. These studies focused on the distribution of food and of receptive females in relation to habitat selection. Erlinge (1983) showed that M. erminea populations are limited by food shortages, whereas Weber (1989) revealed the importance of resting sites for polecats M. putorius during winter. The high mortality of various species of the mustelidae during winter may be as a result of a combined shortage of food and of good resting sites. 22 Sasaki and Ono The Siberian weasel M. sibirica is widely distributed in east Asia, with M. s. coreana the subspecies endemic to the Korean Peninsula and to Tsushima, Japan. It invaded, and spread throughout the western part of Japan, during the 1900s (Milturiya 1969), and has also invaded urban areas. This 'urban' habit is not confined to Japan. Sheng and Lu (1982) showed that in China, female Siberian weasels concentrated in village areas during the breeding season. In our study area, Aoshima, off northwest Kyushu, we compared the village and semi-natural areas which offer different types of resting sites for Siberian weasels. We discuss the factors affecting habitat selection and range size during winter, that is during the non-mating season. Study Area and Methods The study was carried out on Aoshima (33" 25' N, 129" 40' E), an island some 700 m off in the northwest Kyushu (Fig. la). This island is 95 ha in area and its highest point is merely 58111 above sea level. At the center of the island, in area No. 4 (see Fig I.), there is a fishing village of about 500 people. Various habitats are represented on Aoshima : housing area, cultivated fields, paddy fields, grasslands (including abandoned cultivated and paddy fields) and secon- dary forests. Fig. 1. The study area. (a) Areas selected for the distribution survey. (b) Two study areas used for the radio-telemetry survey. I : the northern grassland, I1 : the village area. The dotted area shows the residential area. Habitat Use of Siberian Weasel 23 The distribution and density of the Siberian weasel was surveyed across the whole area of Aoshima. Two study areas were chosen for radio- telemetry : the northern grassland, and the village area, where houses were concentrated (Fig. lb). Outside the village the habitat was divided into grass- land 43.5%, cultivated fields 21.6%, secondary forest 21.4% and paddy fields 10.0% for the grassland. The grasslands consist predominantly of Miscanthus sinensis. The island's secondary forests are characterized by Pittosporum tobira, Litsea japon- ica and Rhaphiolepis uvzbellata, and are often covered by Pueraria lobata. The undergrowth of the secondary forest is sparse, but is dominated by Tra- chelospermum jasminoides. The cultivated and paddy fields are mostly sur- rounded by stone walls of ca. 1 m high. Most of the village area is residential, consisting of houses, barns, school buildings, shrines and a harbor. Trapping Wooden box live-traps were set at a density of four per hectare in the evenings and closed in the mornings during the distribution survey. Traps were checked at midnight to reduce risks of injury to the weasels during the radio-telemetry survey. At each trap site, one trap was placed either on a path or along a stone wall. Dough, spread with mayonnaise, was used as a bait during the distribution survey. During the radio-telemetry survey, the same bait was used in the grassland, but chicken meat with bones was used in the village area, to improve trappability. Captured weasels were anesthetized by an intramuscular injection of Ketamin hydrochloride, Xylazine hydrochloride, and Atropin sulphate. Then they were sexed, weighed, and marked by toe clipping (during the distribution survey), or by freeze-branding and tattooing on the back (during the radio- telemetry survey). Weasels were released after recovery at their capture sites. Judging from the condition of the testis, the non-mating season starts in October and ends in February on Aoshima. Estimation of Population Density Aoshima was divided into six areas (Fig. la), which were trapped in turn from June to September 1982 during the distribution survey. Trappings was also conducted at the beginning of each research period during the radio- telemetry survey. Trapping took place over four or five nights, and the weasel densities were estimated using the removal method (Hayne 1949). The exposed rates were calculated from the number of captured weasels divided by the estimated population number. Radio - telemetry The areas least affected by human activity were the northern and southern areas, but the density of weasels in the southern area was not high enough for telemetric study, thus radio-telemetry was carried out only in the northern 24 Sasaki and Ono grassland (from November 1982 to December 1985), and in the village area (from January 1988 to February 1989). Weasels in the village area were further divided into two groups : those which were located frequently enough to be able to estimate their range sizes, and whose whole range were included in the residential area ("central weasels"), and those which had part of their range in the residential area ("border weasels"). Male weasels were fitted with radio-collars weighing about 20 g, females with collars of about 10 g. The transmitters' frequencies ranged from 50 to 54 MHz. Tracking took place over either for two or three weeks. Weasels were tracked in turn and thus tracking time was broken up over each day. Track- ing times per day varied depending on the number of weasels being tracked. The locations of weasels were determined by triangulation using portable receivers and adcock antennae, throughout the study, however, from 1982 to 1984 three- or five-element Yagi antennae were also used. Location points identified using fixed antennae (the three- or five-element Yagi antennae) were used only for estimating range sizes. Range sizes were calculated using the minimum convex polygon method. Weasels which provided insufficient location points were excluded from the analysis of home range size and habitat use. The weasels which were used for the calculation of range size are listed in Appendix A. Weasel movements, which were observed during tracking, were also recor- ded and used for estimating range sizes. Only the first point of observation on each occasion, and only records one hour or more apart, were used for the analysis of habitat use. Food Habits Feces of Siberian weasels were collected from 1983 to 1985 from the grassland area. Feces were washed over a 1 mm mesh sieve and the remains were identified by stereoscopic microscope. Results Population Density The total number of weasels captured was 38 (29 males and 9 females), and the exposed rate was 92%, excluding area No.6, during the distribution survey. The density in the village, area No.4, was the highest on the island. Newborn males were excluded from the calculation, and we were unable to estimate the density in area No. 6 because trappability was very low there. The population density of the Siberian weasel in each area on Aoshima is shown in Table la. Weasel densities were lower in the grassland than in the village (Mann- Whitney U-test, U=O, p <0.05, see Table lb). The average exposed rates were 95.4% in the grassland, and 89.9% in the village area, respectively. Body Weight Males from the village area were significantly heavier than those from the Habitat Use of Sibe~ianWeasel 2 5 Table 1. Densities of Siberian weasels on Aoshima as estimated by the removal methods (Hayne 1948). (a) Distribution survey in 1982. Males which were less than 470 g were treated as "newborn", as the smallest body weight of reproductive males during the mating season was 470 g ; newborn males were excluded from the calculations.