Abstract
Field tests were conducted in North Dakota in August, September and October 1981 to 1983 inclusive, to determine if decoy plantings of nine sunflower fields and one interplanted corn/sunflower field would reduce blackbird (Icterinae) damage to nearby commercial sunflower fields. Total seed consumption by blackbirds of sunflower (90 ha) and corn (7 ha) was 87860 kg, worth US$26533·72 based on the average 3-year market price of $0·302/kg. The average cost of planting a decoy field was $74/ha for a total cost of $7178. The yearly cost-benefit ratio varied from 1:2 · 1 to 1:4·7 with an overall study average of 1:3·7. From 1981 to 1983, the annual median seed consumption in decoy fields was 917, 1210, and 1121 kg/ha compared with surrounding commercial fields within 11 km of the decoy fields which had losses of 4,99 and 115 kg/ha, respectively. In 1981, a comparison of losses between sunflower fields in Bottineau County and commercial sunflower fields within 11 km of decoy fields provided statistical evidence ( P =0·0651) that there was less damage to commercial fields surrounding the decoy crops; this difference in losses was attributed to the presence of the decoy fields. Average blackbird numbers observed entering decoy fields per minute per hectare were 69 (1981), 49 (1982) and 91 (1983). Peak roost populations associated with decoy fields ranged from 72000 to 215000 blackbirds. Overall, redwings constituted about 83% of all blackbirds observed in decoy fields.
Published Version
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