ADRIAN HAILEY*

SUMMARY

Common lizards (Lacerta vivipara) in summer basked mostly on dry grass during sunny weather, but on pieces of wood when the sunshine was interspersed with periods of cloud cover (changeable weather). In order to determine whether this switch in behaviour could be interpreted as a cost-benefit situation, the effects of different substrates on heating rates at high and low irradiance were investigated. Basking times on wood were related to a number of environmental thermal variables. Heating curves were fitted to a logistic model, which allows description of the complete curve from two basic parameters. Other parameters, such as rate of heating at any temperature, time interval for any temperature interval (or vice versa), and thermal half time, are easily derived from these.