We surveyed 29 wild rice growers, representing 96% of the California acreage grown in 1993, to determine current practices for blackbird damage control. Twenty-seven growers (93%) had blackbird damage. The period of greatest damage and most intensive control was July through September. Red-winged blackbirds (Agelaius phoeniceus) most frequently caused damage, but three other species of blackbirds and the European starling (Sturnus vulgaris) were also identified. Most growers (72%) reported 1 to 10% yield loss. Average loss ranged from $121 to $309/ha, and from $14,530 to $32,061/grower. Most growers (97%) attempted to control blackbirds for an average of 3.5 months during the growing season, relying primarily on shotguns, propane cannons, shellcrackers or bird bombs, and patrols. Growers in northeastern California tended to rate these techniques as more effective than growers in the Sacramento Valley, possibly due to the larger field sizes in the Valley. Average effectiveness ratings for all techniques indicated little better than slight control for the techniques used, suggesting grower dissatisfaction with the available techniques. Average cost for control averaged $86.21/ha, which was among the highest costs for any single aspect of wild rice production.

From commercial fields near McArthur, California, we collected data on methods for controlling blackbird (Icteridae) damage to wild rice (Zizania aguatica). Using and expanding upon an economic model proposed by Dolbeer (1981), we derived economic comparisons of three control programs employing: 1. methiocarb, 2. shooting and propane exploders, and 3. all methods combined. Shooting and propane exploders used together were the most cost effective with a benefit:cost ratio of 2.16:1. Under the assumptions used in the model, methiocarb was least effective with a benefit:cost ratio of only 0.62:1. We discuss assumptions of the model and using basic initial data (cost and efficacy of control, average yield and value of the crop, anticipated damage level) illustrate a format to derive figures for the amount and value of crop to be saved at a given efficacy level, benefit:cost ratios, and net income after control.

Red-winged blackbirds (Agelaius phoeniceus) and other granivorous species cause substantial economic damage to wild rice in California. Currently available damage control techniques have only limited effectiveness and there is considerable need for new effective techniques. We conducted a field trial in northern California to determine the effectiveness of the bird repellent, Flight Control™ (50% anthraquinone), applied at rates of 18.6 and 55.8 L/ha, in reducing blackbird depredations to wild rice. We detected no effect of the treatments on blackbird behavior in the field, even though captive red-winged blackbirds were deterred in feeding trials with wild rice seeds collected from our study plot. We suggest several possible reasons for this: 1) blackbirds used wild rice for cover as well as a food source; 2) birds perhaps received insufficient exposure to the repellent owing to either the birds’ ability to hull the seeds rapidly, low anthraquinone residues on the seeds, and/or non-uniform coverage of seed heads; 3) although Flight Control™ is a feeding deterrent, an aversive response might require repeated exposure to treated rice; and 4) frequent turnover in the depredating population would result in birds not being present long enough to acquire an avoidance response. Clearly, a better understanding of blackbird movements and behavior in wild rice is needed to develop an effective management strategy.

Blackbird species (Icteridae) are considered a primary cause of yield loss prior to harvest in wild rice, which equaled about $3 million in 2007. Although rice consumption should be a null model of bird damage to yield, data from cage traps and point counts indicate that blackbird flocks arrive in wild rice fields 3 to 4 weeks before rice was available for consumption, but coincidental with the time when blackbird form post-breeding flocks. Wild rice plants appear to be attractive habitat from the time the wild rice begins heading until it is harvested (c. 6 weeks), even though wild rice is a food source only for the last 2 to 3 weeks (milk stage to harvest of mature grains). The onset of occurrence in wild rice fields appears to be a function of breeding season of red-winged blackbird and Brewer’s blackbird, specifically they arrive shortly after the time when young-of-the-year become independent of parental care (first week of July). Hence, nesting phenology is the best predictor of blackbird occurrence and their potential damage to wild rice.