Proceedings of the Vertebrate Pest Conference

Farmers have few tools with which to objectively assess the true impact of avian species on crop production, partly because ecologists and conservationists have been slow to quantify the role of birds within agricultural settings. At an annual value of over $5.5 billion dollars, vineyards are the third-most-valuable agricultural crop produced in California. Vineyard area has rapidly expanded in California and now covers at least 820,000 acres. Encouraging growers to retain existing natural habitat around vineyards or install new habitat, such as hedgerows, is likely to have positive effects on biodiversity. However, viticulturists are often wary of actions that could increase wildlife numbers on their land, particularly birds, since they are considered one of the most damaging pests to vineyards worldwide. In California, over 67% of vineyard acres have some degree of bird damage, with estimates ranging from between 5.4% and 16.1% of crops damaged. Conversely, birds may provide vineyards with valuable pest control services by consuming insects in high numbers in the spring and summer. Quantifying these costs (bird damage) and benefits (insect pest control) for vineyards from birds as they relate to natural habitat is an essential step in understanding the net value of nature in vineyard ecosystems. In July 2015, I used a sentinel prey experiment in a California vineyard to measure the relationship between insect pest-control, bird damage, and distance from a riparian corridor. I found that over 40% of sentinel prey were consumed at the edge of the vineyard, and that birds damaged 12% of grapes. Depredation of sentinel prey and grape damage dropped at a similar rate with increasing distance from riparian habitat. These results suggest that birds may remove insect pests at a rate that could offset the damage caused by avian foraging once grapes are ripe, but further studies are needed to confirm this.