User:TheLazyWaffle/Rufous hummingbird

Physiology
The fast-wing beats of the Rufous Hummingbird (Selasphorus rufus) are operated by its two main muscles in the breast region that dictate the up and down stroke of its wings. The pectoralis is the chest muscle which dictates contraction for down-strokes. The supracoracoideus muscle is a muscle above the pectoralis and controls up-strokes for flight. The amount of work done by the immense speed of these contracting muscles require high levels of energy provided by mitochondria. To make up for this, mitochondria occupy an area two hundred times larger than capillaries; in terms of volume, this is almost a third of muscle fibers. Oxygen to the muscle is supplied via a high capillary to fiber ratio. Each muscle fiber has a large number of tiny blood vessels that directly diffuse oxygen to the muscle. The true maximum volume of oxygen intake ( $$VO_2max $$) for Selasphorus rufus has yet to be identified as laboratory experiments do not reflect the true potential of the species. A hypothesis that shedding of the feathers, or molting, places less weight on the bird and therefore maximizes its oxygen intake is one of the reasons. While these systems are unique to the species, other mechanisms such as respiration rate, protein content, and citrate synthase in comparison to mammals are not significantly different.