A QUANTITATIVE STUDY OF DIET IN 3 SPECIES OF RODENTS IN NATURAL AND IRRIGATED SAVANNA FIELDS

During July, 1990 - June, 1992 we collected stomach contents of necrop sied rodents that totalled 494 Arvicanthis niloticus (Desmarest, 1822) , 356 Mastomys natalensis (Smith, 1834) and 273 Tatera valida (Wrought on, 1906) from natural, savanna fields in Nigeria, and 528 Arvicanthis and 367 Mastomys from nearby irrigated fields, where Tatera was never trapped. The materials were processed and microscopically analyzed to determine patterns of diet selection. Sites were sampled for vegetati ve cover and rodent food resources. More than 90% of the stomach mater ials could be identified to one of four categories: dicots (vegetative ), monocots (vegetative), seeds, and insects. Seeds constituted approx imately 50% by mass of foods consumed by all species in both sites dur ing the rains. Mastomys (in both sites) and Tatera maintained the same levels of seed intake year around. Unlike Mastomys, the amount of see ds consumed by Arvicanthis was enhanced by irrigation. In both sites d uring the rains, monocots and insects made up 12-46% and 14-26% of the rodents diet respectively, but their importance diminished in the nat ural site during the dry seasons. Tests of MANOVA indicated significan t species differences and effects of site, season and their interactio ns on foods selected. A few plant species dominated the vegetative cov er, and dramatic differences in the quality of seasonal herbage were o bserved.