Movements, habitat use and response of ricefield rats to removal in an intensive cropping system in Vietnam

Rapid post-control reinvasion typically hampers attempts to manage rodent pests, yet little is known about the demography or behaviours of re-invaders. Here We Study the habitat use and movement of Rattus argentiventer using radio-telemetry during a non-breeding season (tillering growth stage of rice) and a breeding season (ripening stage of rice) in lowland irrigated rice in Vietnam. On two treatment sites, farmers removed rats by hunting, digging tip burrows and by using trap barrier systems (early planted field of rice Surrounded by a plastic fence set with multiple capture rat traps), and on two control sites, farmers conducted their normal control practices. The 95\% minimum convex polygon home range size of rats during the non-breeding period was 2.4 ha (n = 12) and significantly smaller than during the breeding period (9.8 ha; n = 10). There was no difference in home range size between treatment (removal sites) and control sites. During the non-breeding period, rats preferred to use the bank/channel habitat during the day, and preferred vegetable habitats at night. During the breeding period, rats preferred using rice habitats both during the day and at night. This preference during the breeding period was strongly influenced by the availability of abundant cover and food offered by the mature rice crops. Rats were moving about the rice fields in random directions and were not influenced by the removal of rats at nearby locations. We conclude that even at low population densities, rodent control would need to be conducted over large areas to prevent recolonisation through random dispersal events and that rodent burrows should be destroyed during the non-breeding season when little cover is provided by crops.