Graduation Date
Fall 2025
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Wildlife
Committee Chair Name
Dan Barton
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
David Garcelon
Second Committee Member Affiliation
Community Member or Outside Professional
Third Committee Member Name
Matt Johnson
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Nick Som
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Marianas, Spatial capture recapture, Lizard, Predator management, Island, Predator-prey, Adaptive management, Trail camera, Hand capture, Conservation monitoring
Subject Categories
Wildlife Management
Abstract
The Mariana monitor (Varanus tsukamotoi), or hilitiai, is a medium-sized varanid lizard found throughout the Mariana islands. On Islan Dåno’, a small islet off the southwest coast of Guam, hilitai coexist with one of the rarest birds in the world, the Guam rail (Hypotaenidia oswtoni), or ko’ko’, which were introduced to the island in 2010. Since 2009, hilitai have been lethally removed from the island to reduce possible predation on ko’ko’. After 15 years of removal efforts, I sought to 1) estimate the abundance and density of hiltai, 2) assess the effect of removal effort and habitat on hilitai density, and 3) better understand the relationship between hilitai and ko’ko’ to inform wildlife managers. To address the first two goals, I used a spatial capture recapture model that incorporated data from hand captures, camera traps, and telemetry, and used habitat and removal data as density covariates. For the third, I examined camera trap data to describe activity patterns and the stomach contents of removed hilitai. I found a high density of hilitai across the island (~16.3/ha), weak habitat associations, and that hilitai and ko’ko’ are most active at different periods. I did not observe any direct evidence of ko’ko’ predation, though with limited investigation. These findings, in sum, provide wildlife managers with data for adaptive management strategies and establish a baseline for further inquiry.
Citation Style
Journal of Wildlife Management
Recommended Citation
Christie, Jack T., "Estimating Mariana monitor (Varanus tsukamotoi) density with multiple methods on Islan Dåno’, Guam, and its relevance to Guam rail (Hypotaenidia owstoni) conservation" (2025). Cal Poly Humboldt theses and projects. 2510.
https://digitalcommons.humboldt.edu/etd/2510