Improving Bullfrog Capture Methods in Areas Managed for Hawaii's Endangered Endemic Waterbirds

Abstract

American bullfrogs were introduced to Hawaii’s wetlands from California in the late 1800s. As in other areas where American bullfrogs have been introduced, these voracious predators threaten Hawaii’s native fauna. Of particular concern are Hawaii’s federally endangered endemic waterbirds: the Hawaiian stilt, Hawaiian coot, Hawaiian gallinule, and Hawaiian duck. Wetland managers in Hawaii control bullfrogs for the benefit of these endangered waterbirds. The U.S. Fish and Wildlife Service manages several core wetlands on national wildlife refuges in Hawaii that are necessary for survival of the waterbirds. These refuges include bullfrog control as a management strategy. Unpublished studies on James Campbell National Wildlife Refuge have documented bullfrogs as a major predator of newly hatched endangered waterbird chicks. This refuge currently maintains a year-round bullfrog trapping program with increased effort in the spring during the peak of waterbird breeding. Existing trapping methods employ a simple fish-style funnel trap with red flagging used as an attractant. As part of an effort to improve efficacy of current bullfrog capture methods, we investigated the effectiveness of different attractants for the traps. In addition to the current attractant of red flagging, we tested light, bullfrog call acoustic recordings, and life-size bullfrog decoys. The results showed that most of the treatments were no more effective than the control (no attractant). If we can improve bullfrog trap yields, we expect greater chick survival for the endangered Hawaiian waterbirds.