Abstract
This paper describes the food habit and seasonal population changes of Rattus rattus in sugar cane fields on Tokunoshima Island. The volume of ovule integument of the cycad Cycas revoluta, which was commonly planted around the fields, amounted to over 60% of stomach contents of the rats in November and February. The internode of sugar cane was only 12% of the contents in volume even in February when cane matured. The rat population increased in November when cane was immature, and decreased in May when the cane harvest was over. Larger rats were dominantly trapped in November and 76% of the rats weighed over 80g. Smaller or young rats were dominant in February and 61% of rats weighed 60g or less. These results suggest that rats move to the fields in autumn to eat the new ovules, and reproduce in winter under the thick cover of cane.
