Date of this Version
Since the mid-1970s many new and modified damage abatement methods have been implemented to reduce blackbird damage to ripening sunflower in the northern Great Plains. Concurrently, estimates were made of breeding blackbird densities and sunflower damage to track changes in population size and chart progress toward reducing damage. Breeding density estimates were made at both the regional and county levels, whereas sunflower damage estimates were made at the county level only. Periodic regional estimates of breeding densities, between 1967 and 1998, showed that numbers of red-winged blackbirds (Agelaius phoeniceus) and yellow-headed blackbirds (Xanthocephalus xanthocephalus) did not differ among years, while common grackle (Quiscalus quiscula) numbers tended to increase. To improve our ability to detect changes in breeding density, we started intensive county-level surveys in 1996. These surveys, conducted in 4 counties in North Dakota and South Dakota, showed that blackbird densities differed among years from 1996 to 1999. We surveyed sunflower damage in 2 of these 4 counties from 1994 to 1998 and found no difference in damage (Χ̅ = 1.8%) among years. In 1997 and 1998, with an additional 2 counties added to the survey, we again found that damage was similar between years, averaging 2.2%. Overall, breeding blackbird densities have increased in recent years, but dollar loss per hectare trended lower in three of the study counties that had historical databases for comparison. We will continue to use annual estimates of breeding densities and sunflower damage to assess the effects of an evolving integrated pest management program.