Apodiformes  

Hovering in mid air: hummingbirds
 

Hummingbirds hover in flight to gather nectar thanks to several physiological mechanisms.

 
  "Hummingbirds are highly evolved, specialized nectarivores. Their feeding behavior requires the ability for hovering flight, a mode of locomotion that necessitates specific skeletal, muscular, physiological, and metabolic adaptations." (Fowler and Miller 2003:235)

"The most highly specialised of all nectar-feeding birds, however, are South American - hummingbirds...They can beat their wings so swiftly and articulate them so accurately that they can hang in the air in front of a flower." (Attenborough 1995:118)

"Hummingbirds and insects have evolved for sustained hovering flight from vastly different ancestral directions, and their distinct phylogenies underlie the differences in their aerodynamic styles. In all other birds—and, presumably, hummingbird ancestors—the downstroke provides 100% of weight support during slow flight and hovering [hummingbirds today, produce 75% of their weight support during the downstroke and only 25% during the upstroke]. Given that many birds possess the mass-specific power (using anaerobic metabolism) to hover for short periods, the selective pressure on hummingbird ancestors was probably for increased efficiency (resulting in stiff wings with greatly simplified kinematics), and an upstroke muscle (the supracoracoideus) that makes the recovery stroke rapid, while contributing enough to the hovering power requirements to allow the downstroke muscle (the pectoralis) to operate within its aerobic limits. In other words, this pseudosymmetrical wingbeat cycle is good enough, and although hummingbirds do not exhibit the elegant aerodynamic symmetry of insects, natural selection rewards 'good enough' as richly as it does our aesthetic ideals." (Warrick et al. 2005:1096)

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