Gregory D. Kerr

Human Disturbance and Stride Frequency in the Sleepy Lizard (Tiliqua rugosa): Implications for Behavioral Studies

Abstract We report on the influence of observer presence and handling on activity patterns (stride frequency) of the Australian sleepy lizard (Tiliqua rugosa). Over a 17–week period, we maintained continuous records of activity of 10 adult lizards using lightweight activity loggers recording lizard body temperature and stride frequency every two minutes. At all times of day and throughout the season, we recorded the effect of three levels of observer disturbance (observed only, briefly handled [< 60 sec], and held for an extended period [30–45 min]), on lizards either inactive or active at the time of interaction. Following all disturbance types, there was an increase in average stride frequency that lasted for up to an hour. This is a significant period for an animal that is generally active for only a few hours in the day. The extent of this effect was higher for active than for inactive lizards, when observed or briefly handled, and increased with the level and duration of the disturbance. Both inactive and active lizards when held for an extended period responded with a very high average level of activity. We found that shifts to behavior following brief handling (e.g., attaching a cotton spool) can be minimized or prevented by working with inactive lizards early in the morning, when ambient temperatures (and hence lizard body temperatures) are relatively low. Protocol design for field-based behavioral studies involving lizards must avoid, or if necessary compensate, for biases that result from the effect of different levels of observer disturbance on activity patterns.

Field observations of extended locomotor activity at sub‐optimal body temperatures in a diurnal heliothermic lizard (Tiliqua rugosa)

The behavioural response of the sleepy lizard Tiliqua rugosa to an extended drought was examined in spring and summer 2002. Observations of the behaviour and use of microhabitat by radio-tagged lizards for spring in 2000–2002 showed that the lizards in 2002 suffered decreased body mass and increased mortality, were less active, showed reduced mating behaviour and increased use of burrows when compared with the more normal wetter years of 2000 and 2001. The lizards lost significant mass owing to dehydration and starvation. An ‘onboard’ data logger recorded lizard stride frequency and body temperature continuously for 4 months on 11 lizards during the drought of 2002. The normally diurnal heliothermic sleepy lizards responded to rare rainfall events during the drought whenever they occurred, day or night, by emerging from burrows or other shelters for extended periods of activity with sub-optimal body temperatures as low as 8.5 °C. They moved more often, and with higher stride frequencies during periods of rain than during dry periods, both overnight and during the day. As a consequence of this extended activity under physiological stress, the lizards were able to respond to naturally occurring transient opportunities for food and water that would not have been available if they were only active at optimal body temperatures. In an area where freestanding water is rarely available, the lizards were able to access limited water by licking substrate. They also gained water and perhaps nutrition by consuming the temporarily rehydrated thalli of the free-living terrestrial cyanobacterium Nostoc commune . Such behaviour enabled lizards to regain much of the mass lost before the rainfall and probably enabled many lizards to survive until more normal food sources became available. These rare events may have a significant effect on the shaping of the sleepy lizards phenotypic capacities outside routine day-to-day activities.

Microhabitat use by the scincid lizard Tiliqua rugosa: Exploiting natural temperature gradients beneath plant canopies

Abstract Microhabitat use beneath the canopy of perennial woody plants by the heliothermic sleepy lizard (Tiliqua rugosa) was examined at a site near Mt. Mary in South Australia by testing whether the position adopted by lizards under bushes was influenced by their state of activity, time of day, or month. Thirty radio-tagged lizards were followed in 2000 during their spring period of activity (September–November). Lizard position beneath a plant canopy (one of nine sectors) and behavior were recorded for each observation (radio-tagged or random encounter). Active and inactive lizards showed nonrandom use of sectors beneath plant canopies: using mainly the center and north, northeast, and east sectors (northeast quadrant), but this changed with season. Temperature changes beneath plant canopies were measured, these resulted from diurnal and seasonal shifts in the suns position. Temperature gradients in the north-south and east-west axes of bush canopies were shown to shift with time of day and season. Sector use by lizards reflected changing thermal conditions beneath plant canopies. When ambient conditions were cooler, lizards used the warmest northeast quadrant in the morning and the northwest quadrant in the afternoon. During hotter periods of the year lizards were found most often in plant centers. Proportion of records in the center and the southwest increased from September to November, whereas those in the north and northeast decreased over that period. Microhabitat use changed with lizard activity. Active lizards were found less often than inactive lizards in the center of bushes. Inactive lizards tended to avoid southern and western facing sectors. We suggest that, during the extended daily periods of inactivity, sleepy lizards are either selecting a position that has preferred microclimatic conditions within temperature gradients of canopies, or they may have evolved a preference for north and east facing sectors because of a consistent thermal advantage over the course of the changing daily thermal regime in a heat stressed environment.

Ocular Anatomy and Retinal Photoreceptors in a Skink, the Sleepy Lizard (Tiliqua rugosa)

The Australian sleepy lizard (Tiliqua rugosa) is a large day‐active skink which occupies stable overlapping home ranges and maintains long‐term monogamous relationships. Its behavioral ecology has been extensively studied, making the sleepy lizard an ideal model for investigation of the lizard visual system and its specializations, for which relatively little is known. We examine the morphology, density, and distribution of retinal photoreceptors and describe the anatomy of the sleepy lizard eye. The sleepy lizard retina is composed solely of photoreceptors containing oil droplets, a characteristic of cones. Two groups could be distinguished; single cones and double cones, consistent with morphological descriptions of photoreceptors in other diurnal lizards. Although all photoreceptors were cone‐like in morphology, a subset of photoreceptors displayed immunoreactivity to rhodopsin—the visual pigment of rods. This finding suggests that while the morphological properties of rod photoreceptors have been lost, photopigment protein composition has been conserved during evolutionary history. Anat Rec, 2012.