Of Chicks of Arctic-breeding Shorebirds

l. The heat-transfer characteristics of young and adults of several arctic-breeding shorebirds were examined. Heated. skin-covered metal casts were used for measurements difficult to perform on live birds. 2. Heat transfer coefficients are high in small chicks, but decrease rapidly with age. Both heat transfer coefficients and body resistances to heat flow (i.e. insulation) are linearly related to the square root of wind speed. 3. Energy budget analysis indicates that chicks cannot maintain body temperature in typical environmental conditions in the breeding area until at least half grown. During this interval they require periodic brooding by the parent birds. 4. Efficiency of the brooding-activity cycle is enhanced by the thermolability of chicks.