The female goldcrest incubates alone and is not regularly fed by her mate. Incubation starts gradually already during the egg-laying period and may be fully developed before the clutch is completed. From that time onward the hourly mean egg temperature remains remarkably constant, largely independent of time of day and weather conditions. The overall mean egg temperature, recorded during the continuous incubation period, was 36.54.degree. C. The female regulated the temperature of the eggs by adjusting her attentive time. This achieved by varying the duration of the periods-off, which were inversely correlated with air temperature, and varying the duration of the periods-on, which was less influenced by the weather conditions, but was significantly correlated with the time of day (light intensity), on average being shortest during the midday hours.