Measurements of adult brooding behavior
We videotaped nests for about 6 hours starting at 8:50 and ending at 15:00 to collect information on the rate of parental brooding during the heating experiment. Video cameras (Sony Corporation, Tokyo, Japan) were concealed in a corner of the aviary about 3 m away from the nest and were left unattended. Brooding effort was calculated as percentage of time spent by at least one of the parents inside the nest box after excluding the first 10 minutes of recordings to allow adults to resume their normal activity after the initial disturbance caused by positioning the camera. Video recordings were made during the ectothermic phase of growth on day four or five of the nestling stage because brooding behavior is higher during the early nestling stage and often ceases as young get older and approach endothermy.