Field rodent population abundance and cocoa crop loss

C. H. Lee

Abstract

Field rodent population studies in inland cocoa areas adjacent to forest show that the squirrel species Callosciurus notatus, C. nigrovittatus, C. prevostii, C. caniceps, Sundasciurus tenuis and S. lowii are occasional pests and their presence may be limited. Others present were treeshrew (Tupaia glis) and rat species (Leopoldamys sabanus, Maxomys whiteheadi and Stenomys bowersii), forest species that are unable to damage cocoa pods. These animals were absent in cocoa plantings established on the coastal plains except for C. notatus which was noted in limited numbers. For the murids, limited numbers of Chiropodomys gliroides, Rattus rattus diardii, R. exulans and R. argentiventer were noted in both areas. The abundance of R. tiomanicus  is comparable to that of squirrels and increases with the age of cocoa plantings in inland areas adjacent to the forest. In coastal cocoa plantings, it is the dominant and sole rat species present in abundance. A higher level of pod damage with a wider fluctuation in animal population noted in cocoa areas close to forest is attributed to squirrels. The slow and gradual population fluctuation pattern with large numbers of potential breeding rats and low rates of recruitment indicated that birth was more important than immigration. Correlation of body weight to head and body length, and to tail length of the rat had less variation with better accuracy as compared to hind foot and ear length.

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