Fish farmers don't believe their crops are for the birds, but try telling that to a hungry duck, blackbird or heron. ``Birds are a costly problem where fish are cultured,'' says researcher Vickie D. Martin in a new Agriculture Department report. ``Waterfowl frequently blamed for heavy losses of fish at aquacultural facilities include diving ducks, herons, egrets, terns, gulls, kingfishers, blackbirds, ospreys and anhingas.'' These birds _ the diving ducks include grebes, cormorants and mergansers _ were described as ``voracious fish eaters'' that not only cause property loss and damage but can transmit diseases to fish stock. ``Due to fecal contamination and the fact that some of the fish they consumed are diseased, predatory birds may transmit diseases from pond to pond,'' she said. Moreover, when fish farmers attempt to guard against the airborne marauders, they can be frustrated because a majority of the birds are legally categorized as migratory and are protected under federal and state laws. Martin, a student at Fort Valley State College, Fort Valley, Ga., worked as an intern for the department's Economic Research Service the last two summers. Although there are no figures documenting bird predation by fish species and location, she said losses to birds have been reported on baitfish, catfish, shellfish, tropical fish and trout, and are greatest in the largest aquaculture states: Mississippi, Alabama, Arkansas, California and Georgia. ``Baitfish, particularly minnows, are lost to blackbirds in the winter, cormorants in the fall and winter, and herons in the summer,'' Martin said. ``In the Northeast, herons prey on baitfish in the fall, while trout are harassed by grackles, kingfishers, herons, ospreys and occasionally owls during the spring, late summer and early fall.'' She added that diving ducks are the main bird threats to shellfish, although swans occasionally are problems. ``Catfish in the Southeast are preyed upon most by anhingas (locally called water turkeys) and kingfishers during the spring and summer months,'' Martin said. ``Herons and cormorants cause problems year-round. Crawfish and shrimp are prone to predation by purple grackles, herons, egrets, ibises, gulls, diving ducks and kingfishers.'' Fish ponds can be protected somewhat by barriers such as perimeter fencing, netting, overhead wires and other devices, including fireworks, exploders and similar items used to frighten birds. Some chemicals, such as Avitrol, a registered ``frightening agent'' for use on herring gulls and blackbirds, have also been effective, she said. But state and federal permits are required to use this chemical on gulls, because they are legally protected. After ingesting the chemical, the gull ``will behave erratically and emit distress calls,'' which frighten away the other birds, she said. Some migratory game birds may be shot during the hunting season, and other permits are available for some species. Local state and federal wildlife authorities should be contacted. Still, Martin said, some fish farmers believe ``birds are uncontrollable and that all frightening tactics are futile, no matter what method of control of prevention is used.''
