Meeting Abstract
38.3 Jan. 5 Ventilation is metabolically expensive in resting and running guinea fowl MARKLEY, J.S.*; CARRIER, D.R.; University of Utah; University of Utah markley@biology.utah.edu
Avian ventilation may be metabolically costly because the mechanical work required to overcome the inertial and gravitational resistance to movement of the mass of the sternum, associated flight muscles, and viscera is expected to be high. A novel method was used to measure the cost of ventilation (COV) in resting and running guinea fowl (Numida meleagris). Birds� caudal air sacs were cannulated and air was pumped through the lungs and out the nares and mouth (unidirectional artificial ventilation: UAV) until the flow rate was sufficient to decrease ventilatory drive and stop ventilatory movements. The difference in oxygen consumed with and without ventilation was assumed to be COV. The COV of guinea fowl was found to be considerably higher (23% of resting metabolism, 32% of running metabolism) than estimates in mammals and reptiles (1-6% of resting metabolism, up to 15% in running mammals). The high COV measured appears not to be due to UAV inducing metabolic suppression, because expired PCO2 did not decrease drastically during UAV. Additionally, the COV per unit ventilated was the same in resting and running birds (20.3 ml O2 l-1 ventilated), although higher volumes of air were moved in running than resting birds (at rest: minute ventilation 0.31 l min-1 kg-1, tidal volume 16 ml kg-1; during running: minute ventilation 1.5 l min-1 kg-1, tidal volume 25 ml kg-1). These data raise the question of why the ancestors of birds shifted from the primitive mechanism of breathing, which is very economical, to one that consumes more energy.
