A typical "Plateau" stage is present in the rate of oxygen consumption of the semi-altricial griffon vulture embryos

A "plateau" stage in the rate of embryonic oxygen consumption (MO₂) has been described in some altricial avian species. More recently, it has been suggested that the difference in the shape of the curve describing MO₂ vs. incubation length (I) between altricial and precocial birds is only due to the duration of the "plateau" in altricials, it is relatively shorter and unnoticeable in comparison to precocials. In this study, we measured the MO₂ of the developing embryos of the griffon vulture (Gyps fulvus), whose chicks are classified as semi-altricial, where the chick hatches with open eyes, is covered with down, but is unable to stand or leave the nest. Therefore, the question of the presence or absence of a "plateau" in the MO₂ curve vs. I was examined. It was found that in eggs of the griffon vulture, there is a 6-7 days plateau from about day 47 until day 54, just prior to the external pipping. The relatively large mass of the egg (239.8 g ± 23.76 SD, n = 9) and the relatively long I (57 d) enabled enough measurements to detect a typical plateau of MO₂ in vulture eggs. A plateau stage, whose length is proportional to I, should now be considered to be present in all bird embryos.