Abstract
Many reptiles, commonly labelled as ‘nocturnal’, have higher selected body temperatures on a laboratory thermal gradient than are available during their night-time activity period. These purportedly ‘nocturnal’ reptiles experience similar day-time body temperatures (Tb) to diurnal reptiles, suggesting that nocturnal reptiles are capable of thermoregulating during the day. By basking for intermittent periods, utilizing postural adjustments and/or by selecting retreat types for specific thermal qualities, nocturnal reptiles may achieve elevated day-time Tb. To date, no studies have directly examined the diurnal behaviour of a nocturnal reptile in a cool-temperate climate. In this thesis, the diurnal behaviour of the viviparous (live-bearing), nocturnal Otago-Southland gecko (Woodworthia “Otago/Southland”) at Macraes Flat, Eastern Otago, was monitored using time-lapse photography. Time-lapse cameras were set up at deep crevice and superficial rock retreats over two seasons: spring-summer and autumn. Three aspects of behaviour were examined to infer whether the Otago-Southland gecko thermoregulates during the day: 1) basking behaviour, 2) postural adjustments and 3) retreat type selection. Operative temperature (Te) was recorded throughout the study using temperature loggers inserted into copper models. Copper models were used to simulate the Te available to geckos in two basking positions (flat and ‘on-toes’) and in two retreat types (in a deep crevice and under a superficial rock). I discovered that Otago-Southland geckos exhibit a complex array of diurnal behaviours. Both females and males basked and exhibited postural adjustments, yet females had a higher incidence of basking, including the ‘on-toes’ basking behaviour, compared to males. However, there were no differences in the incidence of basking between reproductive and non-reproductive females. Furthermore, no clear differences between basking duration and retreat type were found. In spring-summer basking duration of three out of the four basking behaviours was longer overall for geckos at deep crevice retreats compared to those at superficial rock retreats. However, no differences in basking duration between geckos from different retreat types were evident in autumn. The thermal profiles of copper models indicate that models in basking and in-retreat positions exhibit two distinct profiles. The models in basking positions showed lower temperatures in the early morning and consistently reached higher temperatures in the afternoon, compared to models in retreats. The models in ‘on-toes’ and flat basking positions showed similar heating profiles and reached similar temperatures. Collectively, these findings confirm that the Otago-Southland gecko uses a range of diurnal behaviours, including overt basking, postural adjustments and probably retreat type selection to thermoregulate during the day. The findings of my thesis suggest that more attention should be directed towards the diurnal behaviour of supposedly nocturnal reptiles. In chapter 3, I review the challenges associated with categorising the activity pattern of reptiles. I describe some of the approaches that can be used to study reptile activity patterns and conclude the review with some recommendations for future research on the activity patterns of reptiles.