The Mariana monitor (Varanus tsukamotoi, ne indicus; Chamorro name: hilitai) is a large lizard, growing up to 4 ft in total length, and is an opportunistic predator. They were once considered an introduced species in the Mariana islands, however recent evidence suggests they are endemic. Wildlife managers are nonetheless concerned with potential predation on the endangered Guam rail (Hypotaenidia owstoni, Chamorro name: ko’ko’). The two species co-occur on an islet called Islan Dåno (Cocos Island) off the coast of Guam where the ko'ko' was reintroduced in 2010 after going extinct in the wild in the 1980s. While a control program for the hilitai was implemented in 2009, little is known about their density and distribution on Islan Dano. We used hand captures, camera traps, and GPS telemetry to inform a spatial mark-recapture (SCR) model for estimating the density and abundance of hilitai, evaluating the effect of lethal removal and informing future management actions. Our estimate of 17.5 individuals per hectare is more than twice as high as previous estimates using line-transect methodology. The use of downwards facing trail cameras paired with drift fences detected other rare species on Islan Dåno as well, including the ko’ko’.