Altshuler, D.L.*; Chai, Peng: Hovering performance of hummingbirds in hyperoxic gas mixtures

We present a test of the hypothesis that inspiration of hyperoxic air increases hummingbird hovering performance when birds are challenged aerodynamically. We measured the maximum duration of hovering flight and the simultaneous oxygen consumption of ruby-throated hummingbirds (Archilochus colubris) in low density heliox that was either normoxic (21% O₂) or hyperoxic (35% O₂). As density decreased, hummingbirds in hyperoxia significantly increased hovering duration, down to the density at which birds could no longer sustain hovering flight. At this final density, skeletal muscle activity appears to be anaerobic and independent of oxygen concentration. Hummingbirds in hyperoxia showed no significant increase in oxygen consumption at lower densities. Additionally, we tested the birds ability to discriminate between artificial flowers infused with either normoxic or hyperoxic gases. Even after a full day of training birds failed to associate oxygen concentration with a particular flower, independent of air density. Supplemental oxygen thus yields increased hovering duration but the minimum density at which birds can fly is limited exclusively by aerodynamic considerations.