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First, symposium participants agreed that blackbirds can severely damage sunflower during late-summer migration. Usually sunflower fields located closest to major roost sites are the most vulnerable, creating a situation whereby some sunflower growers receive a disproportionate amount of damage. Surprisingly, the physical and biological characteristics of blackbird roost sites have not been quantified. However, we do know that blackbirds migrating through the prairie pothole region prefer cattail-choked, semipermanent marshes that contain water.

Second, waterfowl use of marshes is limited by dense, tall emergent vegetation (i.e., cattails). Narrow-leaved cattails, which now dominate many marshes, did not invade the entire pothole region until the 1960s and 1970s. Soil erosion has resulted in the siltation of many wetlands, creating shallow basins preferred by cattails. Additionally, prairie fires and grazing by large herbivores no longer control emergent vegetation. The task of finding effective, environmentally safe, and cost-effective methods of managing marsh vegetation is challenging. Quantitative data are needed on the long-term effects of using various marsh habitat management techniques (e.g., burning, grazing, mechanical, and chemical alteration) on the flora and fauna of manipulated marshes.

Third, while the aerial application of aquatic herbicides is one method of quickly reducing cattail densities, widespread use of herbicides will not be accepted by various resource agencies without rigorous testing of their environmental effects. In the mid-1980s, researchers in South Dakota tested the herbicide glyphosate (RodeoR formulation) for managing cattail marshes in South Dakota. Waterfowl numbers on the treated marshes increased significantly. These positive results lead to the current extensive research effort aimed at developing the use of glyphosate for fragmenting cattail marshes. Recently conducted laboratory acute toxicity testing indicated that glyphosate is practically nontoxic and the surfactant used with the chemical is moderately toxic. Field trials showed that aerially applied RodeoR does not effect invertebrate populations. A study designed to answer questions on the effects of decomposing vegetation on water quality should be completed in 1993. Field studies assessing the response of migratory bird populations to altered cattail marshes should be completed in 1993. The effects of fragmenting dense cattail stands on the survival of ring-necked pheasants will be determined from 1992-94. These studies are critical before developing and implementing cattail marsh management plans.

Finally, blackbirds damage 1% to 2% of the sunflower crop each year. If the damage were spread evenly among sunflower growers, these losses would be relatively insignificant. However, about 15% of sunflower growers estimate they incur losses greater than 10%. If a 100 acre field has a production potential of 2,000 Ib/A, a 10% loss (@ $0.10/lb) will cost an owner about $2000. Losses of this magnitude may warrant the use of an integrated pest management strategy which may include (1 ) planting bird-tolerant sunflower, (2) reducing cattail density at local roost sites, and (3) using harassment techniques.

ACKNOWLEDGMENTS

Staff at the Denver Wildlife Research Center, North Dakota Field Station and Department of Zoology, North Dakota State University contributed greatly to the success of the symposium. Dave Bergman used his considerable computer skills to create the cover for the symposium proceedings. Diane Reff spent many hours making arrangements, typing correspondence, and organizing the proceedings. Thanks to the North Dakota and Minnesota Chapter of the Wildlife Society for advertising the symposium agenda. Finally, Dr. Sue Haseltine did an excellent job as moderator.