Body temperatures (Tb) of young white pelicans (Pelecanus erythrorhynchos) were measured in a breeding colony and in the laboratory. The newly hatched naked young were essentially poikilothermic, but an average air temperature (Ta) of over 31 °C was maintained in the colony by parental brooding which usually kept the nest temperature at 26–28 °C. A marked increased in thermogenesis, shivering, and natal down growth occurred by about 13–14 days of age. By 16–18 days, Tb measured after 2 h at 10, 20, and 30 °C in the laboratory ranged from 35 to 40 °C, and was similar to older downy young monitored in the colony. Young were able to gular flutter on the day of hatching, but this was not seen in the colony until 11 ± 2 days of age. Gular fluttering was more common in young exposed to full sun than under cloud. In the sun, gular fluttering began at about 19.5 °C, and increased in frequency with air temperature. Onset occurred at Tb of about 39–40 °C. The onset of functional temperature regulation by about 15–18 days of age correlates with the time that both parents begin to forage overnight, leaving their young unattended.
