Abstract
Regulation of agricultural pests managing their natural enemies represents an alternative to chemical pesticides. We assessed the potential of insectivorous birds as pest regulators in woody crops located in central Spain. A total of 417 nest boxes installed in five field study sites (one vineyard, two fruit orchards, and two olive groves) were monitored for use and breeding of insectivorous birds and other species for four consecutive years (2013–2016). At all field sites except the two olive groves, where birds never occupied the nest boxes, predation experiments were conducted with Greater wax moth (Galleria mellonella) sentinel caterpillars, and food consumption by birds was estimated. Nesting of insectivorous birds, chiefly Great tit (Parus major), and sparrows (Passer domesticus and P. montanus) increased over time, averaging 60% per field site in the vineyard and fruit orchards by the fourth year. Use of nest boxes by sparrows and by Garden dormouse (Eliomys quercinus) was high at the fruit orchards (70%) and the vineyard (30%), respectively. Micro-habitat characteristics (nest box level) and meso-habitat characteristics (patch level) strongly affected use of nest boxes and bird breeding (i.e. number of laid eggs and produced chicks) in different years. Distance to natural or semi-natural vegetation did not consistently affect bird breeding, nor did we see consistent evidence of competition between adjacent breeding birds. Predation rates of sentinel caterpillars were approximately one-third higher near boxes with nesting birds (31.51 ± 43.13%) than at paired distant areas without nest boxes (22.45% ± 38.58%). Food consumption by insectivorous birds per ha and breeding season were conservatively estimated to range from 0.02 kg in one fruit orchard to 0.15 kg in the vineyard. We conclude that installation of nest boxes in Mediterranean woody crops enhances populations of insectivorous birds that regulate pests, but that the effects are moderate and highly context-dependent.
Highlights
The need to maintain and enhance crop yield has led to an increase in agrochemicals use throughout the approximately 12% of the Earth’s ice-free land that is cultivated [1]
Great tit was by far the insectivorous bird species that most often used the nest boxes, accounting for 161 of the 197 (81.73%) reproductive events at the three sites over the whole studied period
Use of nest boxes by sparrows was remarkably high at the two fruit orchards, where use by insectivorous birds was negligible (Fig 2B and 2C)
Summary
The need to maintain and enhance crop yield has led to an increase in agrochemicals use throughout the approximately 12% of the Earth’s ice-free land that is cultivated [1]. More than 2.4 billion tons of pesticides were used worldwide in 2007 [2] Despite their advantages, pesticides can harm biodiversity [3, 4], including organisms beneficial to agricultural production itself (natural pest enemies, pollinators and decomposers [5]), and they can degrade the overall environment by polluting soil and water [6] and promoting soil erosion [7]. An alternative to pesticide use is to regulate pests by maintaining or enhancing their natural enemies [10] This strategy offers a more sustainable agricultural management because it can simultaneously promote biodiversity and ecosystem services other than crop production [11, 12, 13]
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