Revealing microhabitat requirements of an endangered specialist lizard with LiDAR

Abstract

A central principle of threatened species management is the requirement for detailed understanding of species habitat requirements. Difficult terrain or cryptic behaviour can, however, make the study of habitat or microhabitat requirements difficult, calling for innovative data collection techniques. We used high-resolution terrestrial LiDAR imaging to develop three-dimensional models of log piles, quantifying the structural characteristics linked with occupancy of an endangered cryptic reptile, the western spiny-tailed skink (Egernia stokesii badia). Inhabited log piles were generally taller with smaller entrance hollows and a wider main log, had more high-hanging branches, fewer low-hanging branches, more mid- and understorey cover, and lower maximum canopy height. Significant characteristics linked with occupancy were longer log piles, an average of three logs, less canopy cover, and the presence of overhanging vegetation, likely relating to colony segregation, thermoregulatory requirements, and foraging opportunities. In addition to optimising translocation site selection, understanding microhabitat specificity of E. s. badia will help inform a range of management objectives, such as targeted monitoring and invasive predator control. There are also diverse opportunities for the application of this technology to a wide variety of future ecological studies and wildlife management initiatives pertaining to a range of cryptic, understudied taxa.

Ecological Considerations When Designing Mitigation Translocations: An Australian Reptile Case Study

“…To determine the structural microhabitat requirements of E. s. badia , three-dimensional laser scans of uninhabited and inhabited log piles were taken. The laser scanning data were collected using a terrestrial LiDAR scanner, the Maptek TM I-Site TM 8800 (Maptek, Adelaide, Australia), placed in three to five positions around each log pile, depending on how large the log pile was [ 74 ]. The overlapping scans were then merged into a single point cloud for analysis to create a full 360-degree view of target log piles.…”

“…The overlapping scans were then merged into a single point cloud for analysis to create a full 360-degree view of target log piles. The (i) maximum canopy height, (ii) number of logs, (iii) length of log system, (iv) number of branches above and below/adjacent to the main log, (v) log structure height, (vi) diameter of widest hollow, (vii) presence of overhanging vegetation, (viii) position of the log pile (majority resting on ground or raised), (ix) orientation of the log pile, and (x) diameter of the widest section of log were then compared using multiple logistic regression models to determine trends in the types of log piles skinks selected [ 74 ].…”

“…LiDAR analysis indicated that Egernia s. badia has specific microhabitat requirements that must be considered when selecting or modifying an optimal translocation site. Skink occupancy was highest in longer log piles with an average of two logs with some overhanging vegetation, preferably at a mid-storey height and reduced at canopy height [ 74 ] ( Figure 2 ). This is likely to ensure enough space for segregation between members of the skink colony, which vary in size between juveniles, adults and gravid females [ 75 ].…”

“…This is likely to ensure enough space for segregation between members of the skink colony, which vary in size between juveniles, adults and gravid females [ 75 ]. Overhanging vegetation is also likely to be important for providing microhabitat variability, thermal buffering and temperature gradients to support behavioural thermoregulation [ 74 , 76 ]. This is important in an arid landscape with scattered vegetation [ 74 , 76 ], where daytime temperatures can often exceed the upper thermal tolerance limits of most reptiles [ 74 , 77 ].…”

“…In some cases, canopy cover can provide perches for ambush predators [ 74 , 78 , 79 ]. As corvids increased in relative activity and focused their hunting behaviour around log piles inhabited by E. s. badia , this potentially indicates that the trend for log pile selection with reduced canopy cover could be associated with fewer perching options for avian predators [ 74 ].…”