Testing a model for predicting primate crop-raiding using crop- and farm-specific risk values

Crop-raiding by primates is increasingly known to cause conflict between humans and primates, and due to their opportunism, adaptability, intelligence and manipulative abilities, primates can be significant agricultural pests. Levels of crop-raiding are dependent on time of year, crop type, size and location of the farm, and primate species involved, making it difficult for farmers to predict susceptibility to crop-raiding accurately. We use a simple method for calculating the likelihood of crop damage by primates using crop susceptibility to predict the frequency of crop damage for individual farms. The method relies on calculating incidence rates of crop-raiding for individual crops using pooled data from all farms in the sample, and summing these rates as to reach a farm's risk value (RV) to primate crop-raiding. From 273 farms in southwestern Sri Lanka data were collected on crop-raiding by two species of primate, the arboreal folivorous purple-faced langur and the terrestrial frugivorous toque macaque. Data from 93 farms were used to calculate crop-raiding incidence rates for seven commonly grown crops, and we tested the applicability of the model using the remainder of the dataset. Incidence rates of raiding for crops differed for the two species of primate, albeit not in a uniform manner. Farms appear to be more susceptible to crop-raiding by langurs than by macaques, with higher RVs for langurs than for macaques: this is not related to the behaviour of the farmer as for both species four-fifth of the farmers that experience crop-raiding actively chase primates away. Our model using RVs works well for predicting crop-raiding in langurs as crop-raided farms have significantly higher RVs. It works less well for macaques, which may be related to their terrestriallity allowing them to range over larger areas and raid farms opportunistically. (C) 2010 Elsevier B.V. All rights reserved.