An ensemble modeling approach for bird nest counting and 3-D cave modelling at Gomantong, Sabah, Malaysia using terrestrial laser scanning

As far back as early 15th century during the reign of the Ming Dynasty (1368 to 1634), Gomantong cave in Sabah, Malaysia, has been known as one of the largest roosting sites for swiftlet birds (Aerodramus maximus and Aerodramus fuciphagus) and wrinkle-lipped bats (Chaerephon plicatus) in very large colonies. Until recently, no study has been done to estimate the colony sizes of these inhabitants in spite of the grave danger posed to them by human activities and potential loss of the cave to post-speleogenetic deformation. In this study, high resolution terrestrial laser scanning data was used to (i) detect and count bird-nests in cave, (ii) model the cave in three-dimensional (3D) geometry at different resolution scales and (iii) to analyze the cave passage geomorphology. The proposed ensemble modelling approach integrates Taguchi and Objective Function optimization techniques to optimize image segmentation parameters - scale, shape, and compactness. The resulting image objects were classified as birds-nest and cave-wall by exploiting the laser return intensity and the size of image objects. Thereafter, the detection accuracy, reliability and transferability of the method were evaluated. For geometric reconstruction, 3D model of the cave was generated at two resolution scales by using meshing and textured 3D rendering. The models allow investigating the passage network structure, morphometry, geologic rock structure and macro- and micro-geomorhpological features. Result of the detection accuracy yielded area under the ROC curve (AUC) of 0.93 and P<0.0001 at 95% confidence level. Similarly, the tests of heterogeneity using Cochran’s Q and Inconsistency I2 produced p-value of 0.384 and I2 value of 5.10% at 95% confidence interval respectively. Also, the transferability assessment produced overall accuracies of 0.93 and 0.94 AUC and p