Date of this Version
Bird damage to wine grapes was surveyed in nine counties in the coastal area of central California in 1973. Damage to 90 bunches of grapes in each of 14O randomly selected plantings was visually estimated according to seven damage classes. Results indicated that birds damaged or destroyed 1.99%± 1.08% (95% confidence interval) of the crop, or about 1,547 to 5,219 tons of grapes worth more than $0.75 million . Napa, San Benito, and Sonoma Counties had the highest dollar losses. Upper bunches on grapevines were more heavily damaged than lower ones, and dark-colored varieties were more heavily damaged than light-colored ones. Early-maturing and late-maturing varieties were not differentially damaged. Of the birds observed in the sampled plantings , 51.5% were house finches (Carpodacus mexicanus) and 25.8% were starlings (Sturnus vulgaris) ; 16 other species made up the remaining 22.7%. Modifications of the survey methods are suggested for similar surveys of bird damage to grapes and for surveys where higher accuracy is desired.