Enhancing ecosystem services in apple orchards: Nest boxes increase pest control by insectivorous birds

Ecological intensification in croplands aims to enhance biodiversity-based
ecosystem services, helping to increase yield while reducing agricultural
environmental impacts. Identifying ecological intensification tools of
wide applicability and easily implemented by farmers is, therefore, an
imperative. Here, we verify the efficiency of provisioning artificial nest
boxes for insectivorous birds to reinforce pest biological control in
apple orchards. The study was conducted in 24 cider-apple orchards in
Asturias (NW Spain) over three years. We compared the effect of
insectivorous birds between orchards with and without nest boxes occupied
by different bird species, through insectivory estimates based on attack
on a sentinel pest and measurements of arthropod abundance in apple trees.
We also identified preys that birds of different species captured to feed
nestlings. Bird occupancy of nest boxes was widespread, ranging 25.0-33.3%
each year. Great tit was the dominant species, followed by blue tit and,
occasionally, common redstart. Predation pressure on apple pests increased
in orchards with nest boxes, as judged by the increased proportion of
sentinel models attacked by birds (34.9% increase in 2018 and 41.1% in
2019), decreased biomass of tree-dwelling arthropods (-51.7%) and reduced
probability of apple pest occurrence (from 57 to 40%), compared to
orchards without nest boxes. Nesting species showed different predatory
roles in apple orchards. Fewer attacks on sentinel pests but lower
arthropod biomass was associated with blue tit rather than great tit.
Besides, blue tit fed nestlings at a faster rate and included in their
diet a higher proportion of apple pests than great tit, which preyed
mostly on other herbivorous insects. Synthesis and applications. We
demonstrated the usefulness of nest boxes for insectivorous birds in
enhancing biological control of apple pests at a regional scale,
identifying tit species as complementary predators of apple pests and
herbivores. From the farmers’ perspective, providing nest boxes in
orchards may represent an efficient, easy to implement, cheap and
attractive measure of ecological intensification, compatible with other
actions fostering biodiversity in croplands.