Comparison of pyrotechnics versus shooting for dispersing double-crested cormorants from their night roosts

Abstract

Roost dispersal using pyrotechnics has been an effective program for reducing serious cormorant predation problems at catfish farms in Mississippi. Under a recent cormorant depredation order, catfish farmers are also allowed to shoot cormorants at their farms, but not at roosts. To potentially enhance cormorant roost dispersal programs and obtain data about shooting in roosts, I compared pyrotechnics versus shooting for dispersing cormorants from their night roosts. Five pairs of roosts were sequentially selected based on their similarity in numbers of birds and area occupied. By random selection each roost in the pair was harassed simultaneously using either pyrotechnics (screamer sirens and bird bangers) or shooting to kill with steel shot. Harassment of each roost took place during 1.5 hours before sunset and continued for up to three nights to disperse >90% of the birds from the site. During harassment efforts we recorded the number of pyrotechnics and shotgun shells used as well as the amount of time of actual harassment. We then monitored each roost for up to 10 days to assess how quickly birds returned to these sites. We found no difference (P > 0.05) between treatments in the amount of time and shells used to disperse cormorants from their night roosts, or in the number of days post-treatment until birds returned to these sites. However, fewer shotgun shells ((x) over bar =286.6, SE=46.56) than pyrotechnics ((x) over bar =429, SE=81.3) were generally used. Despite deploying only skilled marksmen to shoot cormorants in roosts, relatively small numbers ((x) over bar =45.4, SE=11.14) of cormorants, comprising <5% of roosting populations were killed during consecutive nights of harassment. I conclude that shooting is at least equally effective as pyrotechnics for dispersing cormorants from their night roosts and if included under the cormorant depredation order is unlikely to result in a large number of birds killed.