Gestation Period and Litter Size of Siberian Chipmunk Eutamias Sibiricus Lineatus in Hokkaido, Northern Japan

J. Mamm. Soc. Japan 18(2) : 105-109 December 1993 Scort Communication Gestation Period and Litter Size of Siberian Chipmunk Eutamias sibiricus lineatus in Hokkaido, Northern Japan

Takeo KAWAMICHI and Mieko KAWAMICHI

Department of Biology, Osaka City University, Sugimoto, Sumiyoshi- ku, Osaka 558, Japan (Accepted 1 September 1993)

Clarifying the gestation periods and litter sizes of rodents in natural conditions can be extremely difficult because females give birth in hidden nest chambers. For the Siberian chipmunk Eutamias sibiricus Laxmann, the gestation period, litter size, and the growth of juveniles have previously only been investigated in captivity (Snigirevskaya, 1962 ; Telegin, 1980 ; Blake & Gillett, 1988) ; while those of E. sibiricus lineatus Siebold, which occurs throughout Hokkaido in northern Japan, and Sakhalin Island and the easternmost part of Siberia in Russia (Ognev, 1940) have not so far been studied in either natural or captive conditions. The present study therefore aims to provide information on both the gestation period and litter size of captive and free-ranging E. sibiricus lineatus in Hokkaido, Japan.

Methods

Two pregnant females were captured in June 1984, and one female and one male were captured in October 1987 in the study area (43"55' N, 144"40rE, elev. 3-20 m) located 35 km east of Abashiri City, northeastern Hokkaido, Japan (see Kawamichi, 1980, for a detailed description of the study area). All four were transported to Kyoto (35"Ol' N, 135"44' E, elev. 41 m) in order to study the gestation period and litter size. These four chipmunks and their offspring (three males and eight females) were used in our study. They were kept separately in wire-meshed cages measuring 35 x 40 x 45 cm, and the cages were placed near a window so that they would receive a natural photoperiod and natural air temperatures. A wooden nest box measuring 15 X 16 X 19 cm with a 4 x 4 cm entrance hole was provided in each cage. Sunflower seeds and apples were given as their main food, supplemented with occasional insects. The monthly mean air tempera- ture in Abashiri ranged from - 2.7 "C in February to 19.1 "C in August, while in Kyoto it ranged from 4.0 "C in January to 27.7 "C in August (mean values for 30 years between 1961 and 1990 at the respective meteorological stations). Estrous episodes of wild Siberian chipmunks were observed in the study area over the six years from 1974 to 1979, and in captivity over the five years 106 Kawamichi & Kawamichi from 1989 to 1993. During 1993 four captive females were kept away from males so as to be able to obtain data on their estrous cycles ; and data on the frequency of estrous calls were collected twice from each of two females. Their estrous calls were counted for between four and eight time units (one unit lasted 100 sec) between 11 : 00 and 14 : 00 hrs. Individual marking of animals in the study area (from the year of birth) meant that the age of mothers in the wild was known. Litter size in the wild was estimated from the number of siblings observed emerging from a single nest burrow. The number of young born to three captive females was counted within 55 hrs of their giving birth in 1984 (two litters) and 1989 (one litter).

Results

Estrus and Copulation Fourteen estrous episodes were observed in five captive females between 20 April and 12 June, 1989-1993. On the day of estrus, all females with swollen vulvae uttered distinctive estrous calls. These short "Kruz" calls were repeated at rather constant intervals throughout the daytime for just one day. The two or three captive males all scratched and bit excitedly at the wire of their cages in the direction of the estrous females. The frequency of estrous calls was measured for two females on four days of estrus. One female was heard giving estrous calls on 29 May and 7 June 1993, at a frequency of 65.0 (mean) calls/100 sec (n=7) and 51.8 calls/100 sec (n=4), respectively. The other female was heard calling on 31 May and 12 June 1993, at a frequency of 40.1 (mean) calls/100 sec (n=8) and 25.2 calls/100 sec (n=6), respectively. The frequency of calls on the later dates was notice- ably lower for both females. The overall mean frequency of estrous calls, on these four days of estrus, was 45.4 calls/100 sec (range= 18-84 calls/100 sec). When a door-to-door connection was made between an adult male's, and an estrous female's cage, the male quickly entered the female's cage, ap- proached her while flicking his tail, and mated with her. When estrous females were kept isolated from males on the day of estrus, the females repeatedly came into estrus at a mean interval of 10.2 days (range=9 - 12, n = 5 intervals from four females). The earliest estrus in the year for each female occurred between 20 April and 12 May (x=27 April, n=7 females). Mating was observed in the wild between 17 April and 25 May (8= 10 May, n=32, using data from 1974 to 1979). On the day of mating, one to nine males appeared around an estrous female. Mating calls were rarely heard in the wild (twice on 25 April 1977 and 19 May 1984). Estrous females did not utter estrous calls in the presence of males, hence the frequency of estrous calls in the wild was not recorded.

Gestation Period The gestation period, in the wild and in captivity, was determined to be 30 days on the basis of the following observations. Gestation Period of Siberian Chipmunks 107

1) Copulation between marked individuals was observed in the wild at 13 : 39-13 : 50 on 2 May 1979. The female became pregnant and was sighted frequently until 18 : 04 on 31 May, but she was very inactive on 1 June. When she left her nest burrow at 5 : 45 on 2 June, she was slim and no longer appeared pregnant. It was concluded, therefore, that she had given birth on 1 June after a gestation period of 30 days. Five young chipmunks emerged from their natal burrow on day 36 (7 July). 2) Copulation was also observed in the wild on 19 May 1984. From 15 : 51 to 16 : 26, one pair mated 23 times. Mounting lasted from 3 to 135 sec (X= 15.6, n=16), with 87 % of the 23 mounting bouts being of less than 10 sec duration. At 17 : 26 the male left the female. This female was captured and taken to the laboratory on 4 June. The final confirmation of the pregnancy was at 11 : 31, and the squeaks of seven newborns were heard from the nest box at 13 : 14 on 18 June. The gestation period which was calculated from the time of the first copulation observed was between 715.7 (29 days and 19.7 hrs) and 717.4 hrs (29 days and 21.4 hrs). 3) One of the captive females came into estrus on 24 April 1989. As soon as a male was allowed into her cage, at 16 : 30, copulation occurred. The male was removed from her cage at 16 : 45. The clearly pregnant female was seen carrying nest material into her nest box at 21 : 00 on 24 May, and at 00 : 06 on 25 May the squeaks of two newborns were first heard. This gestation period was between 724.5 (30 days and 4.5 hrs) and 727.6 hrs (30 days and 7.6 hrs).

Litter Size The mean litter size in captivity was 4.7 (range= 2-7, n = 3). The mean body weight of all five newborns from one litter, which were weighed 3 hrs after birth, was 3.7 g (range=3.5-4.0). The body weight of one of the preg- nant captive females was 136 g 19- 20 hrs prior to parturition, and decreased to 115 g 6-7 hrs after giving birth to seven young. The precise litter size in the wild could not be established because the young are all born in underground nest chambers (Kawamichi, 1989). Juve- niles begin to be active outside the nest from day 35, and all siblings remained in the same nest for 45 days after birth (Kawamichi & Kawamichi, 1984). Therefore, the number of siblings observed between days 35 and 45 could be assumed to be the litter size (not taking into account any mortality prior to leaving the nest). On this basis, the litter size of wild chipmunks was a mean of 4.8 (range= 3 - 6, SE = 0.30, n = 13, using data from 1977 to 1989). Litter size did not appear to be correlated with age of females (1 to 6 years old, n= 11, r = 0.42, p> 0.05) as shown in Table 1.

Table 1. Litter size and age of mothers in Eutamias sibiricus lineatus in the wild. Overall mean litter size is 4.8 (n=13). Age in years 1 2 3 4 5 6 Unknown age Litter size 4, 5, 5 4, 5, 5 5 3, 6 6 6 3, 6 Mean 4.7 4.7 4.5 Kawamichi & Kawamichi

Discussion

In the study area, females, including yearlings, come into estrus a mean of 3.0 days after emerging from hibernation (Kawamichi & Kawamichi, 1993). Obvious estrus is observed on only one day per year for each individual female (Kawamichi & Kawamichi, 1984). Presumably, most females in the wild become pregnant on the occasion of their first post-hibernation estrus, thus resulting that estrous episodes were observed only between 17 April and 25 May, whereas in captivity where repeated estrus occurred they extended to 12 June. The gestation period of E. sibiricus in captivity which was determined by Blake and Gillett (1988) is having a mean duration of 31.3 days (range= 28-35, n=56). In their calculations, the day of mating was also included, so the actual gestation period was of 30 days, which coincides with our data. Telegin (1980) found a gestation period of 28 or 29 days for three litters in captivity. The mean litter size in our study was 4.8 in the wild and 4.7 in captivity. In other studies, the mean litter size was 6.1 (range= 1- 12, n = 90 ; Telegin, 1980), and 4.4 at weaning (range= 1-8, n = 176 ; Blake & Gillett, 1988). The mean value given by Telegin (1980) is high, because the numbers of embryos and of placental scars are included. Blake and Gillett (1988) noted that litter sizes in captivity become small in the small size of cages. In the last two decades, E. sibiricus has been imported into Europe, and has been used for the study of reproduction (see Blake & Gillett, 1988). The location and countries of their original stocks are, however, not exactly known and their origins are of significance. Siberian chipmunks imported from Korea and China into Japan as pets were found to utter different estrous calls from those of E. sibiricus lineatus in Hokkaido (Kawamichi, unpublished). Blake (1992) noted three types of estrous calls given by captive Siberian chipmunks : 1) frequency modulated calls (slow calling : 23.3 times/100 sec and fast calling : 243.3 times/100 sec) ; 2) constant frequency calls (20.0 times/100 sec) and 3) two-note calls (23.3 times/100 sec). In our study, only one type of estrous calls was heard, although the estrous calls were not analyzed sona- graphically. The frequency of fast calls noted by Blake (1992) was much faster than that of calls in the present study (18-84 calls/100 sec). Certain differences between results obtained during the various research projects are worthy of note ; the mean interval between estrus was 10.2 days in our study, and 13.6 days (range=ll-21, n=82) as found by Blake and Gillett (1988) ; the number of litters annually was one in our study (Kawamichi & Kawamichi, 1984), but one or two by Telegin (1980) and by Blake and Gillett (1988), depending on the locality according to Telegin (1980) ; and estrous calls differed among different localities. Further studies are necessary to clarify whether these differences are the result of subspecific differences and/or a direct reflection of the effect of local environmental conditions and habitats on the wide-ranging Siberian chipmunks. Gestation Period of Siberian Chipmunks

References

Blake, B. 1992. Estrous calls in captive Asian chipmunks, Tamias sibiricus. J. Mamm., 73 : 597- 603. Blake, B. and K. E. Gillett. 1988. Estrous cycle and related aspects of reproduction in captive Asian chipmunks, Tamias sibiricus. J. Mamm., 69 : 598-603. Kawamichi, M. 1980. Food, food hoarding and seasonal changes of Siberian chipmunks. Japanese J. Ecol., 30 : 211-220. Kawamichi, M. 1989. Nest structure dynamics and seasonal use of nests by Siberian chipmunks (Eutamias sibiricus). J. Mamm., 70 : 44 - 57. Kawamichi, M. and T. Kawamichi. 1984. Maternal care and independence of young Siberian chipmunks. Honyurui Kagaku [Mammalian Science], 48 : 3 - 17 (in Japanese). Kawamichi, M. and T. Kawamichi. 1993. Factors affecting hibernation commencement and spring emergence in Siberian chipmunks Eutamias sibiricus. In Life in the Cold (C. Carey et al., eds.) pp. 81 -89. Westview Press, Boulder. Ognev, S. I. 1940. Mammals of the USSR and Adjacent Countries. Vol. IV. Rodents. 429 pp. (Israel Program for Scientific Translations, Jerusalem 1966). Snigirevskaya, E. M. 1962. The biology of the Siberian chipmunk (~utarniassibiricus Laxm.) on the Amur-zeya Plateau. Zool. Zh., 41 : 1395-1401 (in Russian). Telegin, V. I. 1980. Chipmunks in Western Siberia. Academy of Science of USSR (Siberian Branch), lllpp. (in Russian).