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Large aggregations of birds concentrating around livestock feedyards during fall and winter months have been a common occurrence in many parts of the country (Besser et al. 1968; Dolbeer et al. 1978; Levingston 1967; Palmer 1976; U.S. Fish and Wildlife Service 1976). Extensive utilization of livestock feedyards by these flocking birds has been reported to result in economic losses to the feedyard operator due to feed consumption. In Colorado, seasonal feed losses to starlings obtaining 50% of their daily food at feedlots were calculated to be $84 per 1,000 birds; seasonal losses to red-winged blackbirds (Ageliaus phoeniceus) obtaining 10% of their daily food at feedlots were calculated to be $2 per 1,000 birds (Besser et al. 1968). In Texas, Coon (1974) estimated seasonal feed losses to cowbirds (Molothrus ater) obtaining 30% of their daily food at feedlots to average $35 per 1,000 birds. In California, Palmer (1976) suggested winter losses due to blackbird depredation at an average 10,000-head cattle feedlot to be nearly $5,000 per year. In an earlier California study, Levingston (1967) reported that one million starlings (Sturnus vulgaris) in a California feedlot resulted in losses of $1,000 per day. Williams (1975) reported that redwings, starlings, and cowbirds consume an average of 16.1%, 11.4%, and 20.5% of their respective body weights daily, or about 10.5g, 9.6g, and 9.9g per bird of each species, respectively, per day (avg.=10.0g/bird). Based on these findings, a mixed-species flock of 50,000 birds obtaining 10-50% of their daily food in feed bunkers might consume 50-250kg (110-550lb) of feed per day, or 9,000-45,000kg (10-50 tons) in a 6-month winter period. Either a greater concentration of birds or a greater percentage of their daily food being cattle feed would result in even greater losses. In Idaho, for example, the U.S. Fish and Wildlife reported that starlings alone consumed about 900kg (1 ton) of cattle feed an hour, or about 13,600-18,200kg (15-20 ton) per day. Many questions concerning the utilization of livestock feedlots by winter bird populations as yet need answering. This, then, has resulted in the development of a two-year study just underway in South Texas. The purpose of this study is two-fold: first, to investigate the ecological and economic relationships involved in the daily utilization of South Texas cattle feedlots by several gregarious bird species; and second, to study the effect on daily and seasonal bird population behavior from stress of various bird management tools and strategies. This study is being made possible by partial funding from the Caesar Kleberg Research Program in Wildlife Ecology through the Department of Wildlife and Fisheries Sciences at Texas A&M University; individual support provided by the Texas A&M Agricultural Experiment Station in Uvalde, Texas: the Texas Cattle Feeders Association: and the private cattle feedlots involved.