An ecological study on population structure of rodents was conducted in Alage, Southern Ethiopia. Sherman live traps were used to capture rodents in four habitats and trapping sessions. A total of 684 rodents that represented 11 species were captured. Regarding population size and density, Mastomys natalensis was the dominant species followed by Arvicanthis dembeensis while the least was observed in Graphiurus murinus in the study period. The highest biomass was recorded in A. dembeensis (6771.43 g/ha) followed by M. natalensis (6246.63 g/ha) and M. erythroleucus (3257.14 g/ha) while the least was recorded for G. murinus (10.2 g/ha) followed by Mus musculus (35.36 g/ha).The largest and lowest biomasses per habitat type were recorded for M. natalensis and M. musculus, respectively from bushland. There was variation in the population size, density and biomass among trapping sessions and habitats with the highest estimate in the second trapping session and bushland habitat type. All age groups were represented in the population with seasonal and age group variation. In conclusion, there was variation in population size, density and biomass of rodents among habitats and seasons. These population fluctuations might be mostly due to variation in rainfall, habitat heterogeneity, vegetation cover, reproductive patterns, quality and quantity of food and water.
Key words: Age, biomass, density, population, rodents