Record Details

Burton, Frederic J;Rivera-Milán, F F
Monitoring a population of translocated Grand Cayman blue iguanas: assessing the accuracy and precision of distance sampling and repeated counts
Animal Conservation
Journal Article
Cyclura lewisi
In wildlife translocations, it is important to identify reliable monitoring methods that can provide accurate population estimates for post-release management. We compared density and abundance estimates of distance sampling and repeated counts with complete counts (census data) to determine accuracy (percentage relative bias) and precision (coefficient of variation) for monitoring populations of blue iguanas restored to protected areas on Grand Cayman. We conducted incomplete counts (survey data) of blue iguanas at 12 transects of unequal length (range = 322.1 to 431.7 m) visited 36 times per year, yielding 405 detections in March 2010 and 443 detections in March 2013. Distance sampling and repeated counts provided accurate (range of percentage relative bias = -9.52% to 0.00%) and precise (range of coefficient of variation = 0.10 to 0.15) estimates of iguana density and abundance, and yielded an estimate of the proportion of individuals that were available for detection in the study area during the surveys (Pa = 0.88, se = 0.03). The use of distance sampling and repeated count methods, in carefully designed surveys with representative coverage and adequate replication, can lead to more reliable monitoring of extant wild and translocated rock iguana populations on other Caribbean islands, where individual marking may not be practical, and the proportion of individuals that is available for detection is unknown.