Assessing cost-effectiveness of dissuasion techniques targeting waterbirds in rice fields.

In a scenario of global wetland loss, rice fields are becoming vital habitats for waterbirds, often offering abundant and predictable food resources. However, the increasing presence of waterbirds in rice fields is exacerbating human-wildlife conflicts, as birds are seen as pests by farmers due to the damage they perceive the birds inflict to the crops. To tackle this situation, farmers use dissuasion methods like propane gas cannons, but its effectiveness in reducing damage is often not quantified. In this study we evaluate the cost-effectiveness of propane gas cannons in deterring waterbirds from rice fields and test if there is a correlation between bird abundance in a given field during rice growth and rice yield in the same field. Waterbird counts were conducted before and after dissuasion actions targeting Glossy ibis and White stork in a major rice production area in Portugal. To assess the potential magnitude of damage reduction gained through dissuasion, we estimated the time elapsed between dissuasion events and the reestablishment of bird numbers in the disturbed fields. The economic cost of dissuasion was compared with the estimated gains from reduced damage. Results showed that on average, waterbird numbers recovered ca. 30 min after dissuasion, leading to an estimated 0.78% reduction in crop damage. The final yield of rice production was modelled considering all gains and costs involved in dissuasion actions in relation to an increase in dissuasion efforts for 11 scenarios of potential waterbird damage (0-20%). For dissuasion to be cost-effective, waterbirds would need to destroy at least 17% of the crops, far more than any damage previously recorded in Europe. Also, we found that the abundance of waterbirds in a rice field does not affect rice yield. We suggest that efforts to reduce damage should shift to more cost-effective and environmentally friendly methods, such as diversionary fields or economic compensations to farmers. This can enhance the economies of rice-dependent countries and reduce conflicts, ultimately reconciling rice agriculture with biodiversity conservation.