These data are mark-recapture data procured from conducting nocturnal visual surveys and live lure based trapping for brown treesnakes in the 5 hectare enclosure called USGS Closed Population or Northwest Field North (NWFN). In addition, tissue samples were collected from brown treesnakes in order to build genetic relationships among resident individuals. The population was undergoing acetaminophen based toxicant treatment from March 31 2017 - February 29 2020. Monitoring occurred from 15 October 2016 - 31 March 2020. The data file contains four sheets that report data from different pieces of the demographic response to toxicant applications. Sheet 1 - BTS Count, reports the number of brown treesnakes known to be in the population on a given date. Sheet 2 - IPM, reports demographic values that were used to inform an integrated projection model to estimate population response, elasticity and sensitivity to toxicants. Sheet 3 - Parents, defines and identifies parental relationships between within the 2017 - 2018 cohort of births to other known snakes in the population. Snakes Removed gives the numerical estimate of the number of snakes that were assumed to be have killed by a given toxicant application following failure to subsequently detect them.