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98 WINES&VINES January 2016 GRAPEGROWING 98 WINES&VINES January 2016 Attracting Birds of Prey Nest boxes make it relatively easy to attract predators that help control pests By Nathan Gogoll G rapegrowers can attract certain types of birds to their properties to help deter other pest species. While native birds of prey won't necessar- ily be the free and quick solution to prevent bird damage in vineyards, attracting the preda- tors could be an interesting addition to the strategy. Plus, referring to your local family of barn owls as "vineyard beneficials" seems kind of cool. Advice from the U.S. Natural Resources Conservation Service (NRCS) suggests the in- troduction of barn owl boxes, kestrel boxes and raptor perches could be part of a "multifaceted solution to pest control" that could include other conventional methods such as netting and audible deterrents. The NRCS said barn owls and kestrels are relatively easy to attract to farmland by install- ing nest boxes. Nesting pairs of predatory birds focus their hunting near the nests and will capture increased amounts of prey for their growing chicks. These species are easy to at- tract with nest boxes because natural nesting cavities can be difficult to find. While owls primarily prey on nocturnal rodents, they are known to kill and stockpile more prey than needed. Kestrels, formerly known as sparrow hawks, will hunt large in- sects such as grasshoppers, crickets, beetles and moths, as well as small mammals and birds. Attracting birds of prey may also help with avian pests, such as starlings, by changing their behavior. Additionally, the presence of preda- tors may make pests more cautious and less likely to enter the area to feed. Attending to small details will make a nest box more suitable to attract and fledge birds. Important factors include the number and loca- tion of boxes, timing of box setup, predation and competition, management of the area around the box, and box design. Number of boxes and location Rarely will all the installed nest boxes be oc- cupied in a given year. It is recommended that you put up at least twice as many boxes as the number of nests desired. Territoriality, avail- ability of resources and numerous other factors determine which and how many boxes will be occupied. The idea of putting up more boxes is based on giving the birds options to deter- mine which sites best suit their needs. If a box is not used the first year, wait a few more years to see if it becomes occupied. If a box is consistently not used for a number of years, the location should be changed. For barn owls, the recommended density is up to one box per 5-10 acres; for kestrels, the recom- mended density is up to one box per 10 acres. This density is recommended for areas with ideal habitat and a serious pest problem. Boxes should be put up in areas with clear flight access, preferably away from stands of large trees. Barn owl boxes should face away from the heat of the afternoon sun and be 15 to 30 feet high, and kestrel boxes should face east or south and be 10 to 20 feet high. Boxes should be set up as far away from busy roads as possible, since raptors may get hit by cars while hunting. Timing and competition Barn owls begin selecting nesting territories at the end of winter, but they may take until early autumn to fledge their chicks. Kestrels begin selecting nesting territories later in spring and may not fledge until the end of summer. Set nest boxes up in the selected areas by the be- ginning of the nesting season. KEY POINTS Putting up bird boxes can be part of a grapegrower's overall pest-control strategy. Experts say that owls and kestrels are easy to attract if the nest boxes are placed carefully. The predators will eat rodents as well as large insects, and they can discourage unwanted birds like starlings. Delicato Family Vineyards employs owl boxes at its San Bernabe Vineyard in Monterey County, Calif.