Insectivorous birds are not effective pest control agents in olive groves

Abstract

Although avian-mediated pest control is a significant ecosystem service with important economic implications, few experimental studies have ever documented its role in Mediterranean agroforests. Specifically, information on pest control by birds is lacking in certain permanent agroecosystems of worldwide importance such as olive groves.Here, we assess experimentally for the first time the effectiveness of insectivorous birds in controlling the two main olive-tree pests. We also explore the effects of distance to semi-natural habitat patches on avian insectivore abundance and pest control. We combined bird and pest surveys with pest damage monitoring and two field experiments (branch exclusion and plasticine models) at a regional scale.The experiments showed that birds played a negligible role as pest controllers (measured in terms of attack rates on plasticine models and controlled pest damage) in the studied olive groves; overall, pests were abundant and pest damage was high on most farms. In addition, surveys showed that insectivorous birds were more abundant and diverse in patches of semi-natural habitat, compared to the matrix of olive groves, and that proximity to semi-natural patches was not a driver of bird-driven pest control.This study experimentally demonstrates that insectivorous birds are not effective pest controllers in olive groves. The absence of patterns linking insectivorous birds’ availability and observed pest control suggests that birds are unable to exert effective control over the main olive-tree pests. This lack of biocontrol by birds is probably due to low accessibility and/or appetence for the current insectivorous groups. Habitat improvement aimed at encouraging some under-represented forager species could improve the likelihood that birds will provide this ecosystem service.