Rodent population outbreaks in relation to bamboo flowering in the Chittagong hill tracts, its impacts on crop production and environment

Abstract

In 2006 to 2010 rodent population outbreaks resultant from the 50-year cycle of bamboo flowering were reported in Mizoram, India, the Chittagong Hill Tracts, Bangladesh, and Chin State, Myanmar. The ecological dynamics between rodent population outbreaks and bamboo flowering were studied in Ruma upazila of Bandarban district from March 2009 to December 2011. Small mammal trapping (March 2009 to December 2011) in the villages of Basatlang, Munlai, Mualpi and Neweden was carried out to understand the dynamics of rodent populations in different habitats. The highest percentage of rodent species was captured at community households, followed by bamboo forests, crop field and outside around villages. Ecological survey of bamboo flowering and bamboo seed fall in 2009 found that there were highly significant differences in partially rodent eaten seeds per square meter by month (p=.0001) and positively correlated between total numbers of seed fall and partially rodent eaten seed (r =.611). In 2010 bamboo seed fall survey also found positive correlation (r =.417) between total numbers of seed fall and number of rodent damaged seeds in response to cut, burned and normal bamboo forest. Crop damage assessments found that trap barriers were effective to protect crops from rodent damage during the rodent outbreak. Knowledge, attitude and practice surveys among six ethnic minorities covering 180 households revealed that they had little knowledge about rodent management in field crops and majority of households had severe rodent damage during rodent outbreaks. The study confirms that massive bamboo seed fall increases food availability for rodents, rodents do indeed eat bamboo seeds and the long availability of seed leads to population outbreaks. Particularly Rattus rattus was able to breed for 4-5 months in the forest with animals migrating out in to farmers’ fields as the bamboo seed germinated, causing crop losses of 80-100%. Shortening the time of rodent breeding was possible by cutting and/or burning the bamboo forest at the time of flower initiation as this led to a significant delay in seed production. Implementing large scale bamboo clearance could help prevent the development of population outbreaks or reduce their severity. Although farmers did not feel competent or knowledgeable about rodent management, their main coping strategy of planting earlier ripening rice crops in order to harvest before rodent outbreaks develop, is a sound strategy that should be encouraged during outbreak years. Research on increasing the yield of earlier ripening crops could help manage food insecurity during rodent outbreaks. Trap barrier systems were effective, but implementation costs are currently too high for individual farmers to benefit. Community trapping at the household level was effective for managing post-harvest damage and other household level damages. Although implementation costs are low and reasonable, community trapping requires good organization and leadership to be sustainable.