Measuring body temperatures in small lacertids: Infrared vs. contact thermometers

Infrared thermometers (IRT) are gaining popularity in herpetological thermal ecology due to their several advantages compared to contact thermometers (CT). To evaluate their accuracy in small lacertids, lab parallel measurements using IRT and CT are compared for a set of 52 adult lizards belonging to four different Podarcis forms, including males, pregnant and non-pregnant females, exposed to a photothermal gradient. Skin temperature was measured with an IRT and cloacal temperature with a CT at 10 time intervals, completing 520 paired measurements. Models of the relations were constructed using standardised major axis (SMA) regression. As expected, IRT and CT measurements were significantly correlated but determination coefficients were only moderate, IRT values being systematically higher. Moreover, the SMA regression lines deviated from slope 1 and intercept 0 in all cases, revealing a nonisometric bias; IRT tended to give progressively higher readings than CT for higher temperatures. Results provide methodological insights for further studies on thermal ecology of lacertids.