Vertebrate frugivory in blueberry crops: Patterns across birds and mammals and consequences for yield

Damage and consumption of crops by vertebrates represent a significant source of conflict between humans and wildlife. This is particularly relevant in the context of small-fruit crops, such as blueberries, which are highly conspicuous, small-sized, and situated close to the ground, allowing a wide range of vertebrate species to swallow them whole and in large quantities. In the present study, we assessed the patterns of blueberry consumption by birds and mammals, and the effect of consumption on crop yield, in blueberry orchards in northern Spain. To this end, we characterised the fruit-eating vertebrate community through direct observation and camera traps in blueberry orchards, and conducted exclusion experiments in blueberry cultivars that ripen at different dates. The study was conducted in eight orchards over two consecutive years. We recorded 14 bird species and four mammal species consuming blueberries, with common blackbird (Turdus merula L.) and wild boar (Sus scrofa L.) accounting for more than 80 % of consumption events. Whereas frugivory by blackbirds was observed across orchards and cultivars, blueberry foraging by wild boar was highly localised. The exclusion experiments evidenced a negative impact of vertebrate frugivory on blueberry production. However, this impact was not homogeneous across sites, ranging from no impact to 74 % of yield loss. Similarly, vertebrate impact depended on the cultivar, with the early ripening cultivar being more susceptible to yield losses than late ripening cultivars. Further research is needed to ascertain what extrinsic (orchard and landscape structure) and intrinsic (abundance and physiological requirements of vertebrates) factors are responsible for the observed variability in yield loss across sites and cultivars. In terms of management, we recommend to prioritise bird deterrent methods to minimise the negative impact of vertebrates.