Date of this Version
Human–Wildlife Interactions 9(1):4–13, Spring 2015
Most nonlethal methods available for reducing blackbird (Icteridae) damage to sunflowers rely on fright responses (e.g., propane cannons, distress calls, pyrotechnics, raptor silhouettes) that birds quickly learn to ignore. Chemicals that cause taste or feeding aversions have potential to overcome the spatial and behavioral limitations of frightening methods. Anthraquinone (AQ) is an effective feeding repellent as a seed treatment to deter birds from eating freshly planted grains. In the United States, foliar application of AQ is not permitted on food crops except on small experimental plots. In August 2013, we applied 37.4 L/ha of an aqueous mix consisting of 15.1 L of a prototype AQ product (active ingredient = 25%) per 41.7 L water (5.6 kg AQ/ha). We applied the AQ product by high-clearance ground sprayer on 0.4-ha in a sunflower field in North Dakota. Sunflower development was at the R5.1 to R5.3 stages, or 10 to 14 days before usual onset of blackbird damage. We kept another 0.4-ha plot adjacent to the treated plot as an untreated reference. In early September, we placed 3 red-winged blackbirds (Agelaius phoeniceus) in 6 netted enclosures (2.4 m x 2.4 m x 2.4 m) in each plot. Supplemental rations of cracked corn and water were provided daily throughout the testing period that ended October 1, 2013. Treated enclosures had significantly greater damage (247.4 ± 5.8 cm2) than reference enclosures (214.0 ± 8.6 cm2). Statistical significance implied that AQ increased blackbird damage to sunflowers, contrary to the results of other studies. However, residue analysis of the backs of sunflower heads, bracts (our target areas for the spray), and achenes indicated that AQ residues may have been too low to produce a repellent effect. Our findings suggest that the effectiveness of AQ as a blackbird repellent is context-dependent when applied under commercial-grower conditions.