Date of this Version
Published in G.M. Linz, M.L. Avery, and R.A. Dolbeer, editors. Ecology and management of blackbirds (Icteridae) in North America. CRC Press, Boca Raton, FL. Pgs. 135-158.
Agricultural depredations caused by blackbirds can be managed with various lethal and nonlethal methods, including chemical repellents. For many people, nonlethal chemical repellents represent an appealing approach to managing crop depredation because the depredating birds are targeted but not killed; they are just inconvenienced. An effective repellent application can cause the crop-depredating birds to leave their present feeding site and seek food elsewhere. Where the birds go to feed is immaterial to the producer as long as the birds leave the producer's field. Thus, an effective repellent application will not likely affect the overall size of the blackbird population, but it may reduce the population associated with depredation and thereby reduce losses within the treated field. As a consequence, nearby crop fields might incur greater damage unless appropriate crop protection measures are employed.
Blackbirds flock to fields of rice, sunflower, corn, and other crops because these sites represent accessible sources of abundant and energy-rich food that is obtainable with relatively little effort. Agricultural crops are especially important to young birds and, in the late summer and fall, newly fledged birds constitute a large portion of many depredating blackbird flocks. Crop fields can provide ideal feeding situations for blackbirds learning to fend for themselves. Ever-increasing alteration of the natural landscape to accommodate expansion of human activities makes it increasingly difficult for blackbirds to find natural sources of food. Field crops are powerful attractions to blackbirds, and depredating birds are not easily dissuaded. The potential benefits of feeding on the crop are great, so there must be a commensurately high potential cost to the birds to discourage them.