The Effectiveness of Commercially Available Double-Crested Cormorant (Nannopterum auritus) Deterrent Methods in Reducing Loafing Time on Floating Oyster Cages

Abstract

The Wildlife Services—National Wildlife Research Center Mississippi Field Station, working in conjunction with Mississippi State University, conducted a study to evaluate the effectiveness of several non-lethal, commercial, physical bird deterrents. Deterrents were available on the open market to reduce double-crested cormorant (Nannopterum auritus) (DCCO) roosting time on floating oyster cages. We hypothesized that reducing bird loafing time on floating oyster cages would reduce the potential for bird defecation. Double-crested cormorant defecation can increase coliform counts in both the water and oysters, which could result in oyster farm closure. Shellfish farms often differ from one another due to environmental factors and farm locations. Six deterrent devices were selected as options for farmers, and the amount of time DCCOs occupied floats with deterrents was compared to the time they occupied those without deterrents (i.e., on a control pond). All deterrents except the Scarem Kite significantly reduced or halted DCCO use of floats compared to the control. Of note, the Scarem Kite is the only deterrent that requires consistent wind to operate effectively. The research facility is open-air, but we did not have sufficient wind for proper Scarem Kite function. Thus, it is possible that all deterrents would have produced significant reductions in DCCO use. Our results are encouraging and show that minimal deterrent applications to oyster cage floats can help farms achieve their operational plans’ goals and reduce the potential for pathogen transfer by birds. The data presented here should be considered a starting point for developing an efficient deterrent plan that meets state and federal standards.