Table 2.

Mean values of respiratory frequency, tidal volume, minute ventilation volume, oxygen extraction, and rate of oxygen uptake. Values in parentheses indicate the factorial increase of the variable above the resting value. f_resp, respiratory frequency (min⁻¹); V_T, tidal volume (ml); , minute ventilation volume (l min⁻¹ BTPS, except for fish crow, where it is l min⁻¹ STPD); O_2ext, oxygen extraction; , rate of oxygen uptake (ml O₂ min⁻¹ STPD) during rest and while hovering in two species of hummingbirds, and while flying in a wind tunnel for five other species of birds. The values for during flight in a wind tunnel are the minima that have been recorded. BTPS, body temperature and pressure, saturated; STPD, standard temperature and pressure, dry [1].

	mass (kg)	rest					flight
		fresp	VT		O2ext		fresp	VT		O2ext
hummingbird (>20°C) (Amazilia fimbriata fluviatilis)	0.006	—	—	—	—	—	280	0.63	0.18	0.13	4.1
hummingbird (36°C) (Colibri coruscans)	0.008	—	—	—	—	—	330	0.38	0.12	0.24	5.0
budgerigar (18–20°C) (Melopsittacus undulatus)	0.035	—	—	0.047	0.27	2.62	199	1.15	0.232 (×4.9)	0.26	10.9 (×4.2)
starling (10–14°C) (Sturnus vulgaris)	0.073	92	0.67	0.061	0.28	3.16	180	2.8	0.504 (×8.3)	0.31	28.1 (×8.9)
black-billed magpie (Pica pica)	0.165	52.4	2.95	0.154	—	—	162	6.1	0.953 (×6.2)	—	—
fish crow (12–22°C) (Corvus ossifragus)	0.275	27.3	8.2	0.223	0.19	8.5	120	14.9	1.79 (×8.0)	0.19	68.0 (×8.0)
white-necked raven (14–22°C) (Corvus cryptoleucus)	0.48	32.5	10.5	0.34	0.24	17.0	140	10.7	1.40 (×4.1)	0.29	84.9 (×5.0)