Landscape drivers and effectiveness of pest control by insectivorous birds in a landscape-dominant woody crop

Abstract

Avian-mediated pest control is a significant ecosystem service with important economic implications. However, there is an overall paucity of experimental information about how landscape simplification affect its current level. Information on pest control by birds is missing in some permanent agroecosystems of worldwide importance, like olive orchards, that dominate vast areas in the Mediterranean region. We assess the effectiveness of insectivorous birds for controlling the two main pest insects in olive orchards and explore the effects of landscape complexity and distance to semi-natural patches on avian insectivore abundance and pest control. For this, we combine bird surveys with field experiments (branch exclusions and pest plasticine models) at the regional scale. Landscape heterogeneity increased the abundance and richness of insectivorous birds, which were also more abundant and diverse in semi-natural patches, compared to the farm olive matrix. Experiments evidenced that pest control by birds (measured as attack rates to plasticine models and pest damage) in the studied olive orchards is negligible, while pests were overall abundant and pest damage was high on most farms. This raises alarms about the status of avian pest control in this agroecosystem. Although landscape heterogeneity increased the abundance/richness of insectivorous birds, and favored some forest species, insectivorous bird abundance seems diluted in relation to prey availability in all landscapes. Thus, pest control by birds seems currently unsuccessful in olive orchards. Our results might be evidencing the loss of an ecosystem service due to a generalized massive decline of common and forest insectivorous birds. Key messageO_LIOlive orchards dominate extensive areas causing important landscape simplification. C_LIO_LIInsectivorous birds are more abundant in semi-natural patches within olive farms. C_LIO_LIField experiments show a low impact of birds on olive pests and damage. C_LIO_LIAvian-mediated pest biocontrol seems diluted by limited suitable habitat for birds. C_LIO_LIAgri-environmental measures should focus on increasing landscape complexity. C_LI