Abstract

We studied the impact of restrictions by the thermal environments on body temperatures (T_bs) and microhabitat use of the lacertid lizards Podarcis melisellensis and Podarcis muralis in a Mediterranean area (Croatia) during autumn. The thermal conditions at available microhabitats were assessed with copper models that measured the operative temperatures (T_e) at different sites. We estimated the thermal suitability of microhabitats by quantifying the extent of similarity between the T_es and the range of selected temperatures (i.e., the T_bs that lizards maintain in zero-cost conditions in a laboratory thermogradient; T_sel). Both species maintained, throughout most of day, T_bs that were on average 2–4 C below both T_sel and the T_bs recorded in the field during summer. Nevertheless, the T_bs measured during autumn were in the upper range of available T_es and were much closer to the T_sel than were the T_es. In addition, lizards were most often observed in the warmest microhabitats and were often seen basking. These results indicate that lizards were actively thermoregulating. The T_e measurements show that lizards encounter suitable thermal conditions (i.e., where T_es is within T_sel) in only a restricted subset of the available microhabitats and during only a relatively short period of the day. Thus, lizards are constrained to maintain relatively low T_bs during autumn by the generally low available T_es. Although lizards were clearly thermoregulating, they appeared to accept lower T_bs during activity in autumn than in summer. A possible reason for this seasonal shift in activity T_bs is that achievement of higher T_bs during autumn is only feasible by confining activities to some specific microhabitats, which may severely constrain other behaviors, such as foraging.