ESTIMATION OF SEASONALLY CHANGING GROWTH-CURVES IN WILD JAPANESE FIELD VOLES, MICROTUS-MONTEBELLI

Seasonally changing growth curves were estimated from mark-recapture d ata on the Japanese field vole, Microtus montebelli, using a different iated Gompertz equation. Trapping was carried out at the Kuju Agricult ural Research Center of Kyushu University. The capture-release process was repeated more than 3300 times for 800 individual voles. Young bor n in the summer grew more rapidly and reached a larger asymptotic weig ht than those born in the remaining seasons. The asymptotic mass of yo ung born in November (the last month of the breeding season) was quite small. These young seemed to overwinter in this subadult size. The ma ximum growth rates of the wild voles seemed to fluctuate seasonally, s ynchronizing with the length of daylight. Although the voles born in t he field early in the breeding season became larger than laboratory-re ared voles, they could not achieve the same growth rates as in the lab oratory.