In Arkansas, Lonoke and Prairie counties produce 72% of the United States’ total baitfish and sportfish sales. However, a substantial number (92%) of producers in this region consistently report that common grackles (Quiscalus quiscula; hereafter grackle) and other blackbirds often predate baitfish and sportfish when held in holding vats under sheds prior to shipment and on spawning mats in brood ponds. Despite predation loss due to blackbirds being a producer concern for decades, no studies have quantified the extent of these losses. Therefore, our objectives were to: 1) characterize the foraging patterns (e.g., frequency of visitation, timing, foraging success) of blackbirds within rearing/holding sheds and at spawning mats in brood ponds, 2) measure the amount of prey items consumed by these blackbirds, and 3) quantify the economic impact of predation by blackbirds.
During the 2024 field season, we conducted focal observations and camera surveys on ponds with spawning mats and vats under sheds from five baitfish and three sportfish farms between mid-March - July. Surveys were conducted biweekly, except during the peak of baitfish spawning season from mid-April to mid-May, when they were conducted weekly. Over the nine survey periods, actively foraging blackbirds were collected using air rifles and gavaged with 20 cc of phosphate-buffered saline to stop digestion for subsequent diet analysis. Stomach contents were sorted, identified to lowest classification level, dried at 60°C for 22-24 hours, and weighed to calculate diet type proportions. Twelve grackles were randomly selected for diet analysis through DNA methods.
Of the 111 processed grackles, 71 had consumed fish from ≥5 different species. No fish were observed in the six red-winged blackbirds (Agelaius phoeniceus) collected. Brood pond camera surveys documented nine other avian species, water snakes, raccoons, and mink predating fish on the spawning mats.
We will use multivariate analyses to compare aggregate percentage weight, frequency of occurrence, and prey richness by year, sex, and system (categorical; brood pond or fish shed). Results of this study will be used to guide best management practices for mitigating losses due to avian predation.