Implications of brown tree snake captures from fences

Abstract

The capture of brown tree snakes (Boiga irregularis) from fence lines in the vicinities of air and sea ports is an important component of the integrated approach used for curtailing the dispersal of the species from Guam. Use of fences by brown tree snakes was characterised from over 600 captures of snakes during spotlight searches. Two construction designs of chain-link fences were searched, the difference being whether a horizontal bar or a steel cable was used to support the chain link on top. Both fence designs had snakes concentrated at the fence tops – fences having top bars produced 92% of captures on the top third of the chain link, the top bar, or the parallel barbed-wire strands above the fence; fences without top bars produced 82% of captures from the top third of the chain link or the wires above it. Most snakes were found in a horizontal position and no general trends were found through the night for when snakes ascend or descend the fences. To help concentrate snakes at the tops of fences for facilitating control efforts, we recommend the use of a horizontal bar to support the chain link on top, as well as the use of parallel barbed- wire strands above the fence. We discuss management implications for using searches of fences to control brown tree snakes and to detect new brown tree snake populations in other locales.