Qualitative course of embryonic O2 consumption in altricial and precocial birds

The course of embryonic VO2 was examined in 24 altricial and 27 precocial bird species to test differences in its phenology. Some authors suggest that altricial species lack a plateau in VO2-development found in precocial species. Based on the recently available data we find the following: All species (except members of the family Megapodiidae) exhibit a plateau. Their VO2-development follows an identical basic course which can be described by an exponential increase interrupted by the plateau. There seems to be no fundamental difference between altricials and precocials with respect to the general presence of a plateau. In small altricials the plateau lasts only a few hours. It can be overlooked easily when the measurement is not continuous or when many individual measurements are averaged. However, the plateau-VO2 is lower (about 35%) and shorter (12.4% of incubation time; 16.9% in precocials) in the altricials. Total energy consumption during incubation is 1.9 kJ/g in altricial and 2.2 kJ/g in precocial species.