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Development of Brain Temperature Regulation in the Hatchling Mallard Duck Anas platyrhynchos

Development of brain temperature regulation in mallard ducklings was studied from hatching to 20 days of age to see whether newly hatched ducklings, like adults, maintain brain temperature lower than body temperature. The ducklings were homeothermic at hatching, sustaining a stable body temperature throughout growth at ambient temperatures of 23 and 35 C. The mallard duckling regulated its brain temperature at thermoneutrality as well as during heat exposure immediately after hatching. A significant decrease of brain temperature with increasing body mass (approximately 0.007 C/g) at both ambient temperatures resulted in a significant increase of bodyto-brain temperature difference, indicating that the effectiveness of brain cooling increased with growth. It is suggested that the increased effectiveness of brain cooling with age and body mass is related to the development of the rete ophthalmicum-the avian extracranial vascular heat exchanger responsible for brain cooling in adult birds.