The astonishing flight abilities of hummingbirds are mostly made possible thanks to their highly developed brain representing 4.2% of their weight, the highest ratio of all bird species, but also thanks to a range of anatomical adaptations. Their bones are particularly strong to withstand the mechanical stresses they are subjected to, the flexibility of their joints allows them movements of the wings vertically and horizontally, and the development of their wing-lifter muscles makes propulsion possible both when the wing is up and when it is lowering. Finally, the upper face of the wing, as well as its lower face, play a driving role since the wing can pivot around the axis of the shoulder. In addition, the hummingbird has the particularity of going into torpor during its sleep to rest its body. When awake, its heart beats about 250 times per minute at rest and 1,260 times per minute in flight and its body temperature reaches 104°F (40°C). On the other hand, when it sleeps, its heartbeat and breathing slow down and its body temperature drops to 69.8°F (21°C).