Seasonal and Sex Variations in Live Weights of Captive African Giant Rats Cricetomys gambianus, Waterhouse) in the Northern Guinea Savannah Zone of Nigeria

Adult African giant rats (Cricetomys gambianus, Waterhouse) were live-trapped in Zaria, Nigeria over a period of three years, cutting across all the seasons of each year. They were sexed and weighed immediately after capture, with the aim of determining changes in their live weights with seasons and sex. The overall live weight (MeanSEM) of the African giant rats was 1.210.01 kg (n = 363). The live weight of African giant rats captured during the rainy season (1.170.02 kg) was significantly lower than that during the harmattan (1.250.02 kg; p<0.01) and hot-dry (1.230.02 kg, p<0.05) seasons. The male live weight of 1.280.01 kg was significantly higher (p<0.0001) than that of the female (1.140.01 kg). Male-biased sexual size dimorphism was observed during all the seasons, but was highest during the hot-dry season. The seasonal variation in live weight may be because food was more available in the wild during the harvest (dry) seasons (harmattan and hot-dry seasons) than the planting (rainy) season. The relatively low ambient temperature and relative humidity of the harmattan season was more favourable to growth, which may account for the higher live weight recorded during the season. The sex variation in live weight may be as a result of differential growth rate/time between the sexes. In conclusion, the African giant rats are lightest during the rainy season and the live weight of the male is higher than that of the female regardless of the season.