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

1. Field-based studies on reptile thermoregulation increasingly rely upon p hysical models to estimate operative temperatures. Some investigators use m odels that mimic the size, shape, colour and posture of their study species , but such details may have little influence an thermal regimes land hence, complex models may be a waste of time and money). 2. Temperatures were measured at 10-min intervals inside 48 hollow copper-p ipe models exposed to natural weather conditions over a 27-day period, in a factorial design to examine the effects of model attributes on thermal pro files. 3. These data clarify the ways in which model size, colour (reflectance), o rientation and degree of contact with the substrate affect (a) mean, minimu m and maximum temperatures, and (b) the number of hours per day that the mo dels exceed specified thermal thresholds. Also examined are (c) interaction s between model attributes in these respects, and (d) the ways in which suc h effects depend upon local weather conditions. 4. Model temperatures were affected by all of the attributes tested, but wi th few interactions between these effects. Although statistically significa nt, 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 provide d.