Date of this Version
The double-crested cormorant (Phalacrocorax auritus) is the primary avian predator on the southern catfish industry, estimated to cause $5 million in damage per year. To date, the most effective strategy for alleviating cormorant depredations in areas of intensive catfish production is coordinated dispersal of cormorant night roosts with pyrotechnics. Many of these night roosts are located in waterfowl refuges or wetland habitat leased for waterfowl hunting. Thus, there is an increasing concern about the effects of cormorant harassment efforts on waterfowl and other wildlife inhabiting these sites in cypress-swamp habitat. To address the need for a roost harassment device that was more species-specific, we evaluated two commercially available low- to moderate-powered lasers in a series of large-pen and field trials for their effectiveness in moving cormorants from test ponds and dispersing cormorants from their night roosts, respectively. In pen trials, laser beams directed at small groups of captive birds produced negligible effects, suggesting that the laser light was not highly aversive. This was consistent with a series of veterinary investigations suggesting no detectable ocular damage to cormorant eyes directly exposed to a selected laser at varying distances down to 1 m. During field trials both lasers, directed at roost trees after sunset, were consistently effective in dispersing cormorants in 1 to 3 evenings of harassment and is comparable to the harassment effort needed with pyrotechnics. Because laser treatment is completely silent and can be directed selectively at cormorants, these devices may be extremely useful for dispersing cormorants in sites where disturbance of other wildlife is a concern. Advantages and disadvantages of lasers relative to pyrotechnics are discussed.