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Rocky retreats are limited and geologically constrained resources for rock-dwelling nocturnal lizards. Such lizards should seek retreats that offer thermoregulatory benefits without the risk of overheating during the day, and that protect from predation. For cold-adapted species where air temperature is frequently lower than optimum temperature for performance, factors influencing retreat-site selection and whether future warmer conditions will force superficial rock slabs to be abandoned on hot days remain poorly known. Here, we predicted that retreats selected by a nocturnally foraging, cool-temperate gecko from southern New Zealand would be thermally heterogeneous and that future warmer temperature will force lizards to abandon daytime retreats on hot days. We sampled loose rock slabs (potential retreats) in a tussock-grassland site in all seasons. We measured seasonal rock temperature profiles and field body temperature (T b ) of captured geckos using thermography and quantified the physical characteristics of each potential retreat. We found that both physical characteristics and rock temperatures determine choice of retreats. Field T b of lizards positively correlated with retreat and air temperatures. Also, retreat temperatures, including those of the substrate below the rock slabs, showed complex heterogeneity enabling lizards to choose microsites within retreats to achieve preferred body temperatures intermittently. Observed seasonal shifts in characteristics of occupied rocks imply that lizards choose retreats to maximise warmth in spring, minimise risk of overheating (remain below voluntary thermal maximum, VT max ) in summer and avoid freezing over winter. Our study demonstrates the importance of microclimatic conditions in influencing retreat-site selection. Climate warming might lead to seasonal changes in use of rock slabs and possibly be beneficial initially, but longer-term implications need to be examined., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Understanding the interaction between upper voluntary thermal limit (VT max ) and water loss may aid in predicting responses of ectotherms to increasing temperatures within microhabitats. However, the temperature at which climate heating will force cool-climate nocturnal lizards to abandon daytime retreats remains poorly understood. Here, we developed a new laboratory protocol for determining VT max in the retreat-dwelling, viviparous Woodworthia 'Otago/Southland' gecko, based on escape behaviour (abandonment of heated retreat). We compared the body temperature ( T b ) at VT max , and duration of heating, between two source groups with different thermal histories, and among three reproductive groups. We also examined continuous changes in T b (via an attached biologger) and total evaporative water loss (EWL) during heating. In the field, we measured T b and microhabitat thermal profiles to establish whether geckos reach VT max in nature. We found that VT max and duration of heating varied between source groups (and thus potentially with prior thermal experience), but not among reproductive groups. Moreover, geckos reached a peak temperature slightly higher than VT max in hot weather implying that some retreats must be abandoned to avoid overheating. Our results suggest that cool-climate nocturnal lizards that inhabit daytime retreats may abandon retreats more frequently if climate warming persists, implying a trade-off between retention of originally occupied shelter and ongoing water loss due to overheating.max and with the duration of heating. In the field, pregnant geckos with attached biologgers reached VT max temperature, and temperatures of some separately monitored microhabitats exceeded VT max in hot weather implying that some retreats must be abandoned to avoid overheating. Our results suggest that cool-climate nocturnal lizards that inhabit daytime retreats may abandon retreats more frequently if climate warming persists, implying a trade-off between retention of originally occupied shelter and ongoing water loss due to overheating., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Studies of thermal sensitivity in ectotherms require accurate measurements of body temperature using a reliable device, including in field situations. In this study, we tested the accuracy of a compact and inexpensive mini-infrared thermometer (mini-IRT, 22.3 g) at close distance (within 5 mm) for measuring skin surface temperature of small lizards or their models (painted copper bars). First, we used copper bars to assess the effect of model width on the accuracy of the measurement. We placed the heated models on a cool background, and then surface temperatures were measured with a mini-IRT for comparison with a thermogram from an infrared camera (IRC). We also assessed the accuracy of the mini-IRT for measuring skin temperature for two species of small lizards in the laboratory and in the field, in comparison with the skin surface temperature measured with the IRC and with cloacal temperature measured with a thermocouple thermometer. Our results with inanimate models show that the accuracy of the mini-IRT at a distance within 5 mm is biologically acceptable (within ±1.0 °C of the mean value obtained using a more expensive, calibrated device) when the width is ≥ 7 mm. For live lizards, we observed highly significant relationships between skin surface temperature measured with the mini-IRT and temperatures measured with the two other devices. The mean discrepancies between the mini-IRT and other devices were acceptably small for geckos but larger for the smaller and more slender skinks. Taken together, our results suggest that skin temperature measured with the mini-IRT at a close distance is acceptable for field studies on lizards with an abdominal width ≥7 mm, serving as an inexpensive proxy for core body temperature in situations where portability and affordability of equipment and minimal animal handling are paramount. Nonetheless, calibration of mini-IRTs before use is strongly recommended., (Copyright © 2019 Elsevier Ltd. All rights reserved.)