Integrated management of wintering blackbirds and their economic impact at South Texas feedlots

Abstract

Temporal and spatial use patterns of 2 South Texas feedlots by wintering blackbirds were examined. Economic impact associated with daily foraging was estimated. Effectiveness of 6 selected bird-damage control techniques was evaluated. Costs of the control program relative to potential economic losses were analyzed. Recommendations for cost-effective, bird-damage control programs were proposed. Study methods included direct visual, camera, and radio-telemetric observations of species-specific behavioral patterns along with feed-loss assessments. Five bird species accounted for over 95 percent of the daily bird population. Brown-headed cowbirds alone represented 70 percent. Mean numbers of birds in excess of 50,000 were present daily from October-March. Bird numbers in excess of 100,000 were present daily from December-February. Daily bird numbers peaked in January and February during early afternoon hours with nearly 150,000 birds distributed over 95 percent of the pens and averaging over 1,500 birds per pen. Corresponding diurnal peaks in feed troughs occurred during early morning hours with nearly 10,000 birds distributed over 20 percent of the troughs and averaging over 350 birds per trough. Cattle feed, mostly corn, was a preferred food source of all species, representing over 85 percent of their respective diets. Feed troughs were a preferred feeding site, representing over 70 percent of most of the species' respective feeding times. Cowbirds were responsible for 70-85 percent of the economic feed loss. Seasonal feed loss was estimated at one feedlot at nearly 140t ($18,000). This averaged about 1.9t ($240) of feed consumed per 1,000 birds per season and about 17.61lbs ($1.12) of feed consumed per 1,000 birds per day. Unsynchronized blasts from a network of propane cannons throughout the feedlot, accompanied by occasional use of pyrotechniques, was the most effective bird-damage control program tested. This combination resulted in an estimated 60 percent reduction in bird numbers, 30-50 percent reduction in time spent feeding in feed troughs, and overall 75 percent reduction in economic feed loss. Bird-damage levels of $53 per day, representing a daily bird population of nearly 47,000 birds, was determined to be the lower economic threshold for justification of this program.