Surveillance and reports of Brown Treesnakes on Saipan, 1980-2020

Available active surveillance efforts for Brown Treesnakes on the island of Saipan via nocturnal visual encounter surveys and trapping from 1999-2018 were collected and summarized into 3 csv files (TRAP1999, BTSRRTSaipanTRAP, and BTSRRTSaipanVISUAL). Location and date of non-confirmed reports of snakes 1982-2013 via passive surveillance were compiled into a fourth file (Saipan BTSSightings1980_2020.csv) with their associated credibility score of 1-5 (5 = completely credible) defined by a panel or small group of Brown Treesnake experts. Trapping surveillance efforts used a modified minnow trap as a snake trap. Traps are suspended horizontally from natural vegetation or fences 1-1.5 meter (m) off the ground. Within each trap, a chamber houses and protects a live attractant mouse. Traps are checked each morning, and the grain mix and potatoes providing food and water for lure mice are replenished as needed. Dead mice are replaced immediately when possible, or within two days; dead mice have been shown to be roughly as attractive as live mice for the first 2-3 days. Traps are deployed along transects-which may be the same transects where nocturnal visual surveys occur-and are spaced roughly 20-40 m apart. Visual surveys occur along forest edges, roadsides, and forest interior (via measured and flagged transects). Observers use headlamps to search for snakes in the vegetation or on the ground. Survey transects are sized so that observers can complete one transect per hour (approximately 450 m/hour(h)) and capped at four transects per searcher per night to avoid searcher fatigue. Observers record start and end times, total actual search time, all vertebrates detected (to gain baseline knowledge of snake prey abundance), and distance in kilometers traversed. Surveys begin 30 minutes after sunset. Since 2004, Commonwealth of the Northern Mariana Islands residents have been implored by radio jingles, posters, and trucks with prominent signage to immediately report sightings of snakes. The islands have a Brown Treesnake Hotline with a memorable number (28-SNAKE) to facilitate reporting. Non-confirmed reports of snakes prior to 2004 were obtained via natural resource and port authority agency memos and memory.