H. Jeffrey Homan

IMPACT OF BLACKBIRD DAMAGE TO SUNFLOWER BIOENERGETIC AND ECONOMIC MODELS

We constructed bioenergetic and economic models to estimate the potential impact of Red-winged Blackbirds (Agelaius phoeniceus), Common Grackles (Quiscalus quiscula), and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) on production yields of sunflower in the northern Great Plains of North America. The amount of sunflower consumed annually by males and females, after considering field metabolic rates, energy value and moisture content of achenes, and percentage of sunflower in diets was, respec- tively: Red-winged Blackbirds 277 g and 168 g; Common Grackles 267 g and 230 g; and Yellow-headed Blackbirds 248 g and 139 g. The per capita annual economic damage was: male Red-winged Blackbirds

Evaluation of Bird Shield as a blackbird repellent in ripening rice and sunflower fields

0.09 (U.S. dollars), females

Assessment of Bird-management Strategies to Protect Sunflowers

0.05; male Common Grackles

Response of invertebrates to glyphosate-induced habitat alterations in wetlands

0.09, females

Avian Use of Harvested Crop Fields in North Dakota During Spring Migration

0.07; and male Yellow-headed Blackbirds

Winter Habitat Use and Survival of Female Ring-necked Pheasants (Phasianus colchicus) in Southeastern North Dakota

0.08, females

INFREQUENT COWBIRD PARASITISM ON COMMON GRACKLES REVISITED: NEW RECORDS FROM THE NORTHERN GREAT PLAINS

0.05. Annual loss was

Avian use of rice-baited corn stubble in east-central South Dakota

5.4 + 1.3 X 106 for all three species in aggregate, with Red-winged Blackbirds accounting for 52% of the loss. Blackbird damage represented 1.7% of the dollar value of the 1999 sunflower harvest in the northern Great Plains. This loss would be inconsequential if damage were distributed evenly; however, bird damage is often localized around wetlands and can be economically debilitating to individual producers. Although our model was based on regional population estimates, it should perform well at local scales, provided that a local population can be defined, accurately estimated, and remains stable in size over the six-week length of the damage period. Because of the large numbers of blackbirds that congregate in the region during August and September prior to migration, sunflower pro- ducers should expect some crop losses. The solution to the conflict appears to be one that focuses not on eliminating all damage, but on preventing it from exceeding 5% per field.

Avian Use of Rural Roadsides with Cattail (Typha spp.)

Abstract Chemical repellents sometimes can provide a nonlethal alternative for reducing wildlife impacts to agricultural production. In late summer and autumn 2002, we evaluated Bird Shield™ (active ingredient: methyl anthranilate, Bird Shield Repellent Corporation, Spokane, Wash.) as a blackbird (Icteridae) repellent in Missouri rice fields and North Dakota sunflower fields. We selected 5 pairs of ripening rice fields in southeastern Missouri and randomly allocated treatments (treated and control) within pairs. The repellent was aerially applied by fixed-winged aircraft at the recommended label rate and volume (1.17 L Bird Shield/ha and 46.7 L/ha, respectively); 1 field received 2X the label rate. We observed no difference in average bird activity (birds/minute) between treated and control fields over the 3-day post-treatment period (P = 0.503). We used reversed-phase liquid chromatography to quantify methyl anthranilate residues in treated fields. The maximum concentration of methyl anthranilate in rice samples was 4.71 µg/g. This concentration was below reported threshold values that irritate birds. In North Dakota we selected 6 pairs of sunflower fields used by foraging blackbirds. We randomly selected 1 field from each pair for 2 aerial applications of Bird Shield at the label-recommended rate ∼1 week apart. The remaining 6 fields served as controls. Daily bird counts, starting the first day of application and continuing for 5–7 days after the second application, showed similar numbers of blackbirds within treated and control fields (P = 0.964). We observed no difference in sunflower damage within treated and control fields (P = 0.172) prior and subsequent to the treatment. Bird Shield was not effective for repelling blackbirds from ripening rice and sunflower fields.

American Robins (Turdus migratorius) and Cedar Waxwings (Bombycilla cedrorum) vary in use of cultivated cherry orchards

Even though avian damage to sunflower (Helianthus annuus L.) is a worldwide economic issue, several of the current methods used to reduce sunflower damage were developed and tested in the Prairie Pothole Region of the United States. An intensive research program was conducted in that area because of the regionalized concentration of sunflower production and the severe incidences of blackbird (Icteridae) depredation. During the past 40 years, federal and university scientists tested chemical and physical frightening agents, aversive repellents, bird-resistant sunflowers, decoy crops, habitat management, population management, and cultural modifications in cropping. Some of these techniques have broad applicability and may be useful in depredation scenarios involving other bird species and crops. Population suppression is intuitively appealing, but it typically fails beyond local scales because of avian mobility, population dynamics, and public antipathy. Scare devices, repellents, habitat management, and decoy crops are more likely to meet the test of predictable efficacy and practicality.