-

Bioecological studies of Cricetulus migratorius was investigated in barley and wheat fields during 1996 - 97 in Tehran province. By using the snap traps, population density of C. migratorius was studied in various localities. From among 5 species collected (Mus musculus, Cricetulus migratorius, Apodemus
sylvaticus, Microtus socials, Merion persicus), the C. migratorius was found the second dominant injurious one (24.6%) after M musculus (31.3%). The atmospheric conditions in the month of Ordibehesht (May) caused maximum birth rate which they can reach sexual maturity in months of summer. The average weight of mature female was about 20g. Max. number of litters observed by an individual female has weight between 30 - 40 gr and is 9.5 - 11 cm in body length. Number of litters was found varied from 1 - 10, with an average of 8.6 litters/female in the spring. The young used to feed from
mother milk during the first 6 days of their birth and become sexually mature within 45 - 50 days of their life cycle. C. migratorius rarely tries to make burrows as habitat and generally occupies the other rodents' burrows, mainly M socials. The general structure of the burrows made by C. migratorius is
simple with 2 - 3 entrances. The depth of the burrows was variad depending on the temperature. Max. and Min. depths were recorded 30 and 43 cm in summer and winter seasons respectively. They usually dig the burrows in soft
soil. The burrow is made up of 62 - 65% of plant fiber and 21 - 26% soft soil. The main activity of this animal is confined during night hours to about 22.7 min/hour, while during day time this was recorded only 5.5 min/hour. By
fissuring the burrows it was observed that, more than 1/3 of the burrow was