Wildlife Damage Management, Internet Center for


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Copyright (c) 1983 Mark E. Tobin and Roger L. Hothem


Diurnal abundance patterns of birds were examined in two northern California wine grape vineyards in 1981 and in three other vineyards in 1982. Birds entering the vineyards were counted during day-long censuses conducted one day per week throughout the period of damage susceptibility; grape maturity, ambient air temperature, wind speed, and precipitation also were estimated. Overall, the number of birds of all species entering the vineyards did not vary significantly among six time periods of the day. However, American robins (Turdus migratorius) were clearly most abundant daily before 0930 h, and their numbers generally declined afterwards. House finches (Carpodacus mexicanus) also peaked daily in abundance before 0930 h, but they also reappeared in a second peak during 1730-1830 h. Birds initially were attracted to the vineyards when berry maturity, as determined by sugar content, reached about 11-13° Brix; but overall bird abundance did not appear to be related to grape maturity, air temperature, or wind speed. However, abundance did increase in response to rainfall. A general model predicting diurnal abundance patterns for all species of grape-depredating birds at all vineyards is not possible, but the abundance patterns of some species probably can be predicted at specific vineyards. Growers should monitor bird abundance in their vineyards to determine if and when damage measures are most needed.