Rodent outbreak in relation to bamboo flowering in north-eastern region of India

Rodent outbreaks have been recorded in the north-eastern hill region of India since time immemorial. This study was carried out in Arunachal Pradesh where rodent outbreaks are associated with Dendrocalamus hamiltonii, Dendrocalamus strictus, Bambusa tulda, Bambusa balcoa and Schizostachyum arunachalensis. Four species of rodents are reported in the flowering area of which Rattus rattus is predominant and causes greatest damage to many crops. The greatest damage recorded in rice ranged from 12.9% to 15.4% in the bamboo flowering year, whereas it was 5.3% to 5.8% in the non-flowering year. Higher levels of damage were also observed in maize, pineapple, cabbage, French bean, potato, tomato and tapioca in bamboo flowering affected area than in other areas. Live burrows count, trap index and percent damage revealed that in bamboo flowering areas, the rodent population was significantly increased. The comparison of nutrient content of bamboo seeds and other food materials suggested that higher carbohydrate content of the bamboo seeds triggered the active behaviour of rodents. Damage was caused only to those crops which are a very good source of carbohydrate. The cumulative effects of rainfall, flowering season, hunting of predatory animals or birds and geographical barriers might be responsible for the outbreak of rodents. The study also explains why every flowering season does not result in a rodent outbreak of the same severity.