In many parts of Africa rodent depredation on growing rice has been the cause of distressing losses. In rain-fed fields near Tarauni, northeast of Kano, Nigeria, the Nile rat, Arvicanthis niloticus and the Multimammate rat, Mastomys natalensis, are major rodent pests involved in upland rice damages. The objectives of this work were to determine the proportion of rice damaged at selected growth phases and maturation (=yield loss); differences in amount of damage between rice varieties; and relationship between abundance of rodents to scale of damage. Methods involved random selection of four replicates of ha-1 plots each of two varieties, namely, FARO-54 and FARO-58. In each plot were at least 676, 2m X 2.5m or larger planting beds (Clusters) from which 246 were randomly selected, meeting 95% confidence value for sample size estimates. From each cluster 25 hills were randomly selected for damage counts using Cut-Tiller-Count method. A mix of Burrow-Count and other rodent abundance indices along five replicates of 300m x 2m transects were selected to estimate rodent densities after calibrating the values of the indices to known population sizes drawn from capture-removal and regression analysis. Mean yield loss was up to 13%, with significant differences at P<0.05 in damage between rice varieties, rice growth phases and population densities. Rodent density estimates were 48-108 animals per ha-1, with statistically significant relationship to magnitude of damage. Investigations such as this were thought to offer vital data for crop insurance and other agro-financial decisions.
Keywords: Arvicanthis niloticus, rice depredation, Mastomys natalensis, Nigeria, rodent population