Feeding Behavior and Diet of Free-ranging Black-crowned Night Herons on a Catfish Aquaculture Facility in Mississippi

The impacts of many species of piscivorous birds on aquaculture are well documented in the southeastern United States; however, specific studies of black-crowned night heron (Nycticorax nycticorax) in these areas are lacking. Because black-crowned night herons opportunistically exploit abundant food resources and inhabit an important catfish production area, we initiated a study to assess their use of and potential impacts on a catfish aquaculture facility. We conducted a biweekly survey October 2004-September 2006 on Harvest Select Farms near Inverness, Mississippi, to quantify year-round patterns of free-ranging night heron presence and collected 75 night herons for stomach content analysis. We also documented nocturnal behavior by night herons twice weekly June-September 2004-2006 on these ponds During the summer and early fall each year, we observed approximately 85 night herons per biweekly survey. The most common behavior observed on ponds each year was standing and waiting. Night herons numbers declined at Harvest Select Farms beginning in November and use of ponds ended by January of each year. Night heron use resumed in late spring (April 2005) or summer (June 2006) with peak abundance occurring in September of each year. Stomach content analysis (n = 75) revealed 72% of stomachs contained catfish fingerlings, ranging from 0-26 fingerlings/stomach. Mean number of catfish/stomach (n = 63) was 3.95 (SE = 0.58). Mean length of fingerlings was 9.8 cm (n = 159, SE = 0.19), and mean weight was 11.0 g (n = 159, SE = 0.59). A review of pond health records revealed that 53% of birds collected were on diseased ponds. Mean number of fingerlings found in stomachs of night herons collected on diseased ponds (4.36; SE = 0.99) was greater than healthy ponds (2.14; SE = 0.37; t40 = 2.09, P = 0.043). Night herons' ability to rapidly exploit distressed catfish fingerlings during disease outbreaks may prevent fisheries managers from capturing the true loss to disease in their inventories. Although we documented consumption of catfish and use of the farm as a foraging area, their actual economic impact is unknown without additional studies to assess the issue of compensatory mortality

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