Preserving frugivorous birds in agro-ecosystems: lessons from Spanish olive orchards.
Frugivorous birds are a priority for conservation. They are experiencing the transformation of natural habitats to agro-ecosystems worldwide and some are taking advantage of agricultural production of fleshy-fruited plants. However, the mechanisms through which some birds are able to thrive in agricultural landscapes while others become extinct are poorly known. This manuscript provides an overview of avian frugivory in olive orchards, one of the principal agro-ecosystems in the Mediterranean region and an important winter refuge for birds. The hypothesis that Mediterranean avian frugivores are pre-adapted to olive orchards is used to consider potential constraints to bird occupation of wider agro-ecosystems. Agricultural practices and artificial selection of fruit cause habitat and landscape simplification and reduction of bird food resources in orchards, with resulting negative effects on bird diet and body condition, as well as on bird abundance and diversity. Some of these constraints can be partially overcome by the presence of small hedgerows and copses in the agricultural landscape. Five pre-adaptive features determine the successful occurrence of a bird species in olive orchards: (1) frugivorism intensity; (2) ability to track variation in fruit availability; (3) diet plasticity to cope with low fruit diversity and unbalanced food; (4) fruit handling plasticity to cope with oversized fruits; and (5) ecomorphology and foraging niche conditions which increase the ability to respond to habitat simplification. Synthesis and applications. Management practices have the potential to alleviate the constraints that habitat simplification puts on bird movement and diet. Two inter-related approaches to management are proposed: increasing landscape and habitat diversity by the occurrence of hedgerows and forest remnants; and increasing food availability through reducing the use of pesticides and promoting fruit diversity in hedges.