Infra-red irradiance and set point temperatures in behaviourally thermoregulating lacertid lizards

1. 1. Set point temperatures at which Podarcis muralis and Lacerta vivipara ceased basking (T_move; upper set point) and commenced basking (T_bask; lower set point) increased incrementally with increasing i.r. irradiance; values for all set point temperatures were higher in the former species.

2. 2. Changing the i.r. irradiance during a bask resulted in a shift in the upper set point temperature to a level intermediate between the values expected at constant previous and new irradiances (experiment with L. vivipara only).

3. 3. The changes in set-point temperatures following changes in i.r. irradiance were not due to changes in light intensity.

4. 4. The ability to respond to immediate changes in i.r. irradiance is adaptive for lizards in areas in which rapid changes in amounts of sunshine are a feature of the climate.