Field studies of reptile thermoregulation: how well do physical models predict operative temperatures?

1. Field‐based studies on reptile thermoregulation increasingly rely upon physical models to estimate operative temperatures. Some investigators use models that mimic the size, shape, colour and posture of their study species, but such details may have little influence on thermal regimes (and hence, complex models may be a waste of time and money). 2. Temperatures were measured at 10‐min intervals inside 48 hollow copper‐pipe models exposed to natural weather conditions over a 27‐day period, in a factorial design to examine the effects of model attributes on thermal profiles. 3. These data clarify the ways in which model size, colour (reflectance), orientation and degree of contact with the substrate affect (a) mean, minimum and maximum temperatures, and (b) the number of hours per day that the models exceed specified thermal thresholds. Also examined are (c) interactions between model attributes in these respects, and (d) the ways in which such effects depend upon local weather conditions. 4. Model temperatures were affected by all of the attributes tested, but with few interactions between these effects. Although statistically significant, the effects of model attributes upon operative temperature regimes were generally minor (<5% of mean values). 5. Guidelines for the use of physical models in future research are provided.