For Fewer Insect Pests, Invite Bluebirds into Your Vineyard
By Tina Gheen
Readers of this site are probably already familiar with bird-friendly® coffee, but what about bird-friendly wine? Can birds and vineyards coexist in a mutually beneficial arrangement?
Winemaking is big business in the state of California. Over 1 million acres of land has been converted for agricultural or urban uses due to the expansion of vineyards in the past 60 years. Much of this land was originally oak woodlands and savannahs, which are home to the western bluebird (Sialia mexicana).
Western Bluebird
© Michael R. Duncan
The western bluebird is an insectivore that nests in the cavities of oak trees. Its diet consists of arthropods such as moths, butterflies, grasshoppers, crickets, and beetles. Scientists from the Smithsonian Migratory Bird Center and the University of California Santa Cruz wondered if the bluebirds' taste for insects could be used to a vineyard's advantage.
After all, a family of bluebirds (5 nestlings and 2 adults) can easily consume 124g of insects a day! And vineyards are susceptible to a variety of insect pests, such as the light brown apple moth (Epiphyas postvittana), the European grapevine moth (Lobesia botrana), and the beet armyworm (Spodoptera exigua), which would make a tasty meal for a hungry bluebird. Instead of using pesticides to control the insect pests, why not employ birds for the task?
The scientists set up an experiment to test the idea. They divided two organic vineyards in half and installed nest boxes on existing trellises along the grapevines on one half of each vineyard. With the addition of the nest boxes, the team found the number of insectivorous birds increased dramatically. The overall abundance of insect-eating birds quadrupled, and the number of bluebirds increased by a factor of 10. Three species were most commonly found in the boxes—western bluebirds, tree swallows, and violet-green swallows—but, not surprisingly, the bluebirds were by far the most dominant species, occupying 75% of the nest boxes.
Installing the nest boxes certainly increased the number of birds in the vineyard, but what about the pest control aspect? The team needed a way to discover if the birds could take care of a insect pest control problem. They decided to conduct a sentinel prey study.
In a sentinel prey study, the prey (in this case insect larvae) are in some way immobilized or tethered so research teams can easily make calculations about predation rates without risking agricultural crops. Beet armyworm larvae were set out on pieces of cardboard for six hours a day in the morning on both halves of the vineyards. Then the team waited and watched.
The researchers found 2.5 times more larvae were taken from the areas with nest boxes than the control areas without boxes. And they found 3.5 times more larvae were removed from the study areas below bluebird nest boxes than in the control areas.
The experiment in the California vineyards was a great success, both for increasing the bird population and controlling pests without pesticides. The study demonstrates how conservation practices can benefit growers as well as birds. Adding nest boxes to the rows of grapevines significantly increased the number of insectivorous birds in the area, which in turn resulted in a decrease of insect pests along the crop rows. But this type of natural pest control isn't just limited to vineyards.
Agricultural growers across the US can support bird conservation while taking advantage of pest control services provided by insect-eaters, such as bluebirds, by placing nest boxes along annual crop rows.
Building upon the success of bird-friendly® coffee, organic vineyard owners can potentially target an established eco-friendly consumer market with their bird-friendly wine. The economic and ecological advantages of employing a bird-friendly pest management strategy can clearly benefit growers, consumers, and the environment.
This article summarizes the information in this publication:
Jedlicka JA, Greenberg R, Letourneau DK, 2011 Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards. PLoS ONE 6(11): e27347. doi:10.1371/journal.pone.0027347
Insectivorous Western Bluebirds (Sialia mexicana) occupy vineyard nest boxes established by California winegrape growers who want to encourage avian conservation. Experimentally, the provision of available nest sites serves as an alternative to exclosure methods for isolating the potential ecosystem services provided by foraging birds. We compared the abundance and species richness of avian foragers and removal rates of sentinel prey in treatments with songbird nest boxes and controls without nest boxes. The average species richness of avian insectivores increased by over 50 percent compared to controls. Insectivorous bird density nearly quadrupled, primarily due to a tenfold increase in Western Bluebird abundance. In contrast, there was no significant difference in the abundance of omnivorous or granivorous bird species some of which opportunistically forage on grapes. In a sentinel prey experiment, 2.4 times more live beet armyworms (Spodoptera exigua) were removed in the nest box treatment than in the control. As an estimate of the maximum foraging services provided by insectivorous birds, we found that larval removal rates measured immediately below occupied boxes averaged 3.5 times greater than in the control. Consequently the presence of Western Bluebirds in vineyard nest boxes strengthened ecosystem services to winegrape growers, illustrating a benefit of agroecological conservation practices. Predator addition and sentinel prey experiments lack some disadvantages of predator exclusion experiments and were robust methodologies for detecting ecosystem services.
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