Wildlife Damage Management, Internet Center for
Date of this Version
November 1979
Abstract
During August and September in 1977 and 1978, we monitored the feeding patterns of radio-equipped, male red-winged blackbirds (Agelaius phoeniceus) and associated blackbird flocks in the vicinity of Fuller’s Lake Waterfowl Production Area in Steele County in east-central North Dakota. Fuller’s Lake, a cattail marsh of about 1,000 acres (405 ha), serves as the main roosting area for a blackbird assemblage that, for the past seven years in late summer, has numbered from 100,000 in wet years to more than 750,000 in dry years. Sunflower is an important crop in the Fuller’s Lake area, being grown on about 20 percent of cropland. Wheat and barley are other major crops, grown on about 40 percent of the cropland. Corn is grown on less than 1 percent of the cropland, but the number of quarter-section (160-acre, 65 ha), irrigated cornfields increased in the area from two in 1977 to eight in 1978. The Fuller’s Lake area lies on the eastern edge of the North Dakota Drift Plains and is poorly drained, with as many as a dozen water basins per square mile. This combination of a large roosting marsh and numerous satellite roosting and loafing marshes, intermingled with sunflower fields, has created optimum conditions for blackbirds to damage some sunflower fields. Damage was estimated at 23.6 percent of the sunflower crop in a 28-section area surrounding Fuller’s Lake in 1972 (Besser and Guarino 1977), when little control effort was expended. Experiments were conducted with 4-aminopyridine baits as a frightening agent to protect sunflowers from blackbird damage in a 7-township (3-county) study area in the Fuller’s Lake area in 1977 and 1978. In 1977, 31 of the most heavily damaged fields were baited with Avitrol® FC-Corn Chops 99S (Henne 1978), but in 1978 only five were baited (Henne et al. 1979). These experiments afforded us an excellent opportunity to monitor the feeding patterns of blackbirds frightened from ripening sunflower fields as well as undisturbed birds. In some instances, when a feeding pattern had been established by a flock in an untreated ripening sunflower field, we frightened the flock from the field by mechanical means. This paper presents the major findings of this 2-year study.