Preparation and Analysis of Alternative 4-ap Baits for Blackbirds

Red-winged blackbird (Agelaiu^ phoeniceus) acceptance of corn as a bait for use in ripening sunflower has been questioned. This study demonstrated that sunflower meats, sunflower achenes, and pearled barley all have potential as alternative bait carriers for 4-AP. Each can be treated with 4-AP so that individual bait particles carry dosages equivalent to those of cracked corn in the registered product, Avitrol FC Corn Chops 99S. Treated baits produced a distress response in redwings in times ranging from 21.7 min (sunflower meats) to 64.5 min (sunflower achenes). The time to distress elicited by sunflower meats coated with 4-AP was similar to that obtained with cracked corn baits used in the commercial product. Simulated rainfall or contact with moist soil resulted in a loss of 4-AP from all treated baits. Sunflower achenes proved the most durable of the baits, retaining 75% of their original 4-AP content following 1/4 in of simulated rainfall. INTRODUCTION Blackbirds invade ripening sunflower and corn fields in flocks which can number in tens of thousands. Avitrol FC Corn Chops 99S is a commercial product used to disperse these flocks. It consists of chopped corn bait where one in 100 particles is treated with 3% 4aminopyridine (4-AP). Distress behavior results from birds ingesting a treated particle, and the subsequent vocalizations and erratic flights are intended to frighten the remaining flock from the baited field. Success depends upon bait acceptances, two important aspects of which are probably a (1) fast response time to treated TI U. S. Fish and Wildlife Service, Denver Wildlife Research Center, Bldg. 16, Denver Federal Center, P. 0. Box 25266, Denver, Colorado 80225-0266 birds, and (2) number of birds exhibiting distress behavior at the same time. Avitrol FC Corn Chops 99S has given inconsistent results when tested in ripening sunflower (Guarino 1974 unpubl. rept. No. 45/2/, Besser and Cummings 1975 unpubl. rept. No. 59, Henne et al. 1979, Jaeger et al. 1983). Poor bait acceptance by the principal pest species, the Red-winged Blackbird (Agelaius Phoeniceus), is believed to be an important reason. Field observations and tests indicate that sunflower achenes or meats (Knittle et al. 1985 unpublo rept. No. 202), millet (Besser 1981 unpubl. rept.), and pearled barley (Burst and Cunningham 1982 unpubl. rept. No. 230) are all more readily accepted by redwings than is cracked corn. However, more information is needed on the quantitative and qualitative chemical properties of these baits. This paper describes (1) the treatment of each of these four alternative baits with 4-AP, (2) the laboratory analysis of treated baits, (3) the bioassay results on caged redwings, and (4) bait durability with respect to moisture. We would like to thank Ed Schafer, Roger Bui lard, and Mike Jaeger for reviewing the manuscript, and Dave Otis for the statistical analysis. METHODS AND MATERIALS Bait Preparation Sunflower and millet whole seed were soaked in a solution of 4-AP, the edible seed being impregnated through the hull in this manner. Sunflower achenes (200 g) were placed in a sealed container and soaked for 72 hr in a solution of 5.0 g 4-AP, 87.3 ml methanol, 2.7 ml water, and 5.0 ml HC1. After soaking, the achenes were drained and Yi Unpublished reports cited here refer to Bird Damage Research Reports available upon request from the Section of Bird Damage Control, Denver Wildlife Research Center, Denver Federal Center, Denver, Colorado 80225.