Lung Ventilation and Temperature Regulation in the European Coot Fulica atra

Consumption of O₂ (V̇o2), production of CO₂ (V̇co2), respiratory frequency (f), tidal volume (VT), total inspired ventilation (V̇I), body temperature (Tb), and expired air temperature (Te) have been measured simultaneously in the coot, Fulica atra (mean body weight 0.398 kg), at ambient air temperatures (Ta) ranging from -25 C to 35 C. Below the lower critical temperature (20 C),V̇o2 increased according to the equation V̇o2 (ml O₂ kg⁻¹ min ⁻¹) = 37.52 − 0.97 Ta. At Ta of −25 Ca ventilation increase of 60% was markedly disproportional to the three- to fivefold increase in V̇o2. This implies a reduced air convection requirement (V̇I/V̇o2) of 48%. At Ta of 35 C, f doubled while VT remained nearly unchanged. A nearly unchanged V̇o2 associated with the increased V̇I at 35 C implies a functional bypass of the parabronchial segments of the lung. Expired air temperature shows a decline nearly parallel to an isothermal line between Te and Ta. At Ta of −10 C or lower, Te was within 2 C of zero. The respiratory responses to changes in Ta are discussed in terms of heat economy, showing that actual respiratory heat loss is only 9.6% of the theoretical maximum at −25 C. While 79.7% (at −25 C) can be ascribed to cooling of expired air, 10.7% is due to reduction in V̇I/V̇o2.