DOI: 10.5061/dryad.vmcvdnczh
title: Activity of tjakura (great desert skinks) at burrows in relation to plant cover and predators

description: Increased predation where ground cover is reduced after severe wildfire is
 increasingly implicated as a factor causing decline of vulnerable prey
 populations. In arid central Australia, one species detrimentally affected
 by repeated wildfire is the great desert skink or tjakura (Liopholis
 kintorei), a distinctive lizard of the central Australian arid zone that
 constructs and inhabits multi-entranced communal burrows. We aimed to test
 whether tjakura or predator activity at burrow entrances varied
 with cover and how tjakura respond to predator presence. Using
 time-lapse photography, we monitored tjakura and predator activity at the
 largest entrance of 12 burrows ranging from high (&gt;70 %) to low
 (&lt;50 %) cover and at multiple entrances of two other burrows.
 Overall activity did not vary between burrows with high and low cover.
 Within burrow systems, tjakura were more active at sparsely vegetated
 entrances, often sitting wholly or partly inside the burrow. However,
 consistent between and within burrow systems, skinks spent proportionally
 more time fully outside where cover was higher. Predators – mostly native
 – were detected at most burrows, with no apparent relationship between
 predator activity and cover. Skinks also did not appear to modify their
 activity in response to predator visits. Our results indicate that tjakura
 may spend more time outside burrow entrances when cover is higher, but
 there was no direct evidence that this related to perceived or real
 predation risk. Differences in food availability, thermoregulatory
 opportunities, and opportunities for ambush foraging associated with
 differences in vegetation cover or composition are other factors likely to
 be important in determining the activity of tjakura at burrows.
  Our research demonstrates the usefulness of camera traps for
 behavioural studies of ectothermic burrowing animals. The complex
 relationships between tjakura activity and vegetation cover were
 thereby revealed, suggesting outcomes of fire-mediated habitat change on
 predator-prey interactions are not easily predictable.
description: Data was collected via
 camera trapping.  Data
 Analysis The images were
 initially sorted into three categories: one or more
 <em>tjakura</em> visible, other vertebrate
 species visible, or no vertebrate visible. The images with skinks present
 were then divided into three position categories: fully inside the burrow
 entrance, half emerged with front legs visible, or fully emerged from the
 burrow entrance, with hind legs visible outside (Fig. 2). There were three
 clearly distinct size classes of
 <em>tjakura</em> in the images including
 very small, medium, and large or adult size, so we were able to<em>
 </em>assign individuals<em> </em>into three approximate
 age classes; juvenile (current year hatchlings), sub-adult, or adult.
 Where there were two or more
 <em>tjakura</em> in the image, each was
 classified separately for size and position. We were not always able
 to distinguish among different individuals from the same burrow. However,
 obvious differences in size, colour, the presence of distinguishing
 features (e.g. part of the tail missing), or the presence of multiple
 individuals in single images allowed us to determine a minimum number of
 individuals present at each burrow during each recording
 period.  Activity at burrows in
 relation to burrow characteristics and vegetation 
 Repeated measures
 analysis of variance was used to determine whether the minimum number of
 individuals varied between the two recording periods (within-subjects
 effect) or between burrows with high and low vegetation cover. We then
 used Pearson correlations to test how
 <em>tjakura</em> activity at the main
 burrow entrance related to the minimum number of lizards occupying the
 burrow, the number of entrances in the burrow system, and vegetation cover
 at the burrow. Response by
 <em>tjakura</em> to predator activity at
 burrows All vertebrates known or
 suspected to be predators
 of <em>tjakura</em> were included in
 analyses. The number of discrete ‘visits’ by predators to burrows was
 determined based on the sequence of images. If the same predator was
 visible in consecutive images, this was counted as a single visit. We then
 tested for correlations between vegetation cover at burrows and the number
 of predator visits. To determine whether
 <em>tjakura</em> reduced their activity in
 response to predator visits the relationship between active bouts of
 skinks and predator visits was first interpreted graphically. The activity
 of skinks before and after predator visits was compared based on (a) the
 time interval (min) between a
 <em>tjakura</em> being visible and the
 arrival of a predator and the interval (min) between a predator leaving
 and a <em>tjakura</em> becoming visible
 again, and (b) the number of active bouts
 by <em>tjakura</em> in the 24 hours prior
 to predator arrival and post predator departure. The null hypothesis (no
 effect of predators) was that there would be no difference in the 24 hours
 before and after a predator visit in the time interval between
 <em>tjakura </em>activity and predator
 activity<em> </em>or the number of
 <em>tjakura</em> active bouts. Time data
 were log-transformed prior to analyses. Daily activity patterns
 of <em>tjakura</em>
 To investigate patterns
 in daily activity we plotted the time <em>tjakura</em> spent outside the burrow against the average activity of <em>tjakura</em> in the early and late active seasons. The early active season was considered as the time between <em>tjakura</em> first emerging during spring until end of December and the late active season as roughly January to March.  We then split the data into dawn, day, dusk and night. Dawn and dusk were defined as an hour-long period during which sunrise and sunset occurred. In late 2014 dawn fell approximately between 0500 and 0600 (sunrise range 5:47am – 5:49am) and in early 2015 dawn fell between 0600 and 0700 (sunrise range: 6:15am – 6:58am), and dusk in both years was approximately between 1900 and 2000 (sunset Nov/Dec range: 7:19pm – 7:32pm, Jan/Feb: 7:39pm – 7:31pm) (Australian Government Bureau of Meteorology, http://www.bom.gov.au, accessed July 2021). We used a 3-factor repeated measures ANOVA with time (dawn/day/dusk/night) and vegetation (low/high) as the fixed factors and burrow site as a random factor nested within vegetation and Tukey’s post hoc test was used for pair-wise comparisons. To do this, we converted number of images to images per hour to account for the different lengths of each period.  <em>Tjakura</em> activity at multiple entrances within a burrow system Two additional burrows were selected from the remaining eight of the 20 active burrows; one (Burrow A) with four entrances and one (Burrow B) with seven entrances. Reconyx cameras were set up at every burrow entrance in the same way as described previously.  Width, height, opening, diameter, and height (cm) of the mound, as well as percentage cover of vegetation in a 1m<sup>2</sup> quadrat centred over each entrance were measured and the main entrance was identified, according to previous protocols.  Activity at burrow entrances was recorded at all entrances simultaneously for 4 days in early February 2015. Cameras were set to time-lapse taking 1 picture per minute. One camera (at Burrow A, Entrance 1) malfunctioned, and that entrance was excluded from all analyses. We used correlations to test whether the level of activity at burrow entrances was associated with burrow size, minimum number of individuals using the system, overall activity, and vegetation cover at each entrance.
description: All data files are in CSV format.