All of the mechanical power estimates used in these calculations of flight muscle efficiency were calculated using aerodynamic models ( Chai et al., 1998 Chai and Dudley, 1995 Norberg et al., 1993 Ward et al., 2001). Flight muscle efficiency ranges from 13% to 23% in the European starling, from 11% (during hovering) to 15% (during forward flapping flight) in a nectar-feeding bat and from 10% to 13% in the ruby-throated hummingbird ( Archilochus colubris) during hovering ( Chai et al., 1998 Chai and Dudley, 1995). Variation in both the postural cost of flight and muscle efficiency with flight speed would result in a non-linear relationship between mechanical and metabolic power.Ĭomparisons have been made between mechanical and metabolic power requirements of flight across a range of flight speeds, assuming that the postural costs consist of 10% of the metabolic cost, in order to examine flight muscle efficiency ( Chai et al., 1998 Chai and Dudley, 1995 Norberg et al., 1993 Ward et al., 2001). ( Ward et al., 2001) found that flight muscle efficiency ranges from 13% to 23% with flight speed, and flight muscle efficiency may also increase with bird body size ( Ward et al., 2001) as has been shown in flying insects ( Casey and Ellington, 1989). However, this may not be an accurate assumption (in particular given that the energy expenditure of physiological systems other than the heart and respiratory system, and muscles other than the pectoralis muscles have not been considered) and may vary with bird size and flight speed. Others have assumed that the additional energy expenditure includes basal metabolism and an additional 10% of the metabolic cost of flight, based on estimates of the energy consumed by the heart and respiratory system in flight ( Pennycuick, 1975 Pennycuick, 1989 Tucker, 1973 Ward et al., 2001). The actual postural cost of flight is unknown. Thus, the relationship between the mechanical and metabolic power requirements of flight may vary with flight speed because of changes in the postural costs of flight and changes in muscle efficiency. The ‘postural costs’ of flight encompass the energy expenditure above basal metabolism of all non-muscular physiological systems and muscles other than the pectoralis muscles. The mechanical power requirements of flight give us insight into the demands of flight in relation to flight speed however, the generation of mechanical power by the pectoralis muscles does not represent the sole use of metabolic energy during flight. Consequently many aspects of a bird's physiology, ecology and behaviour are affected by the demands of flight. However, it is probable that previous estimates of the postural costs of flight have been too low and that the pectoralis muscle efficiency is higher.įlight is one of the most energetically demanding forms of locomotion ( Schmidt-Nielsen, 1972), consuming energy at high rates. The pectoralis muscle efficiency (estimated from mechanical and metabolic power, basal metabolism and an assumed value for the ‘postural costs’ of flight) increased with flight speed and ranged from 6.9% to 11.2%. Although the mechanical and metabolic power–speed relationships had similar minimum power speeds, the metabolic power requirements are not a simple multiple of the mechanical power requirements across a range of flight speeds. Similar to measurements of the mechanical power–speed relationship, the metabolic power–speed relationship had a U-shape, with a minimum at 10 m s −1. In order to estimate in vivo flight muscle efficiency, we measured the metabolic cost of flight across a range of flight speeds (6–13 m s −1) using masked respirometry in the cockatiel ( Nymphicus hollandicus) and compared it with measurements of mechanical power determined in the same wind tunnel. Animal flight provides a unique model for determining muscle efficiency because only one muscle, the pectoralis muscle, produces nearly all of the mechanical power required for flight. One of the main problems with determining in vivo muscle efficiency is the large number of muscles generally used to produce mechanical power. Little is known about how in vivo muscle efficiency, that is the ratio of mechanical and metabolic power, is affected by changes in locomotory tasks.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |