Peters Susan E, Dobbins Charles S
Department of Biology, The University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA.
J Morphol. 2012 Mar;273(3):312-23. doi: 10.1002/jmor.11024. Epub 2011 Oct 24.
A comparison of the isometric forces and levers of the pectoralis muscle in red-tailed hawks (Buteo jamaicensis) and barred owls (Strix varia) was done to identify differences that may correlate with their different flight styles. The pectoralis consists of two heads, the anterior m. sternobrachialis (SB) and the posterior m. thoracobrachialis (TB). These are joined at an intramuscular tendon and are supplied by separate primary nerve branches. As in other birds, the two heads have distinct fiber orientations in red-tailed hawks and barred owls. SB's fiber orientation (posterolateral and mediolateral from origin to insertion) provides pronation and protraction of the humerus during adduction. Electromyographic studies in pigeons show that it is active in early downstroke and during level flight. TB is more active during take-off and landing in pigeons. The anterolateral orientation (from origin to insertion) of its fibers provides a retractive component to humeral adduction used to control the wing during landing. In our study, the maximum isometric force produced by the combined pectoralis heads did not differ significantly between the hawk and owl, however, the forces were distributed differently between the two muscle heads. In the owl, SB and TB were capable of producing equal amounts of force, but in the hawk, SB produced significantly less force than did TB. This may reflect the need for a large TB to control landing in both birds during prey-strike, with the owl maintaining both protractive (using SB) and retractive (using TB) abilities. Pronation and protraction may be less important in the flight behavior of the hawk, but its prey-strike behavior may require the maintenance of a substantial TB for braking and controlled stalling, as it initiates strike behavior.
对红尾鹰（Buteo jamaicensis）和横斑林鸮（Strix varia）胸肌的等长力和杠杆进行了比较，以确定可能与其不同飞行方式相关的差异。胸肌由两个头组成，即前侧的胸肱肌（SB）和后侧的胸臂肌（TB）。它们在肌内腱处相连，并由独立的主要神经分支供应。与其他鸟类一样，红尾鹰和横斑林鸮的两个头具有不同的纤维方向。SB的纤维方向（从起点到止点为后外侧和中外侧）在内收过程中提供肱骨的内旋和前伸。对鸽子的肌电图研究表明，它在早期下扑和水平飞行时活跃。TB在鸽子起飞和着陆时更活跃。其纤维的前外侧方向（从起点到止点）为肱骨内收提供了一个回缩成分，用于在着陆时控制翅膀。在我们的研究中，鹰和鸮的胸肌头组合产生的最大等长力没有显著差异，然而，力在两个肌肉头之间的分布不同。在鸮中，SB和TB能够产生等量的力，但在鹰中，SB产生的力明显小于TB。这可能反映了在捕食攻击时，两种鸟类都需要一个大的TB来控制着陆，鸮同时保持前伸（使用SB）和回缩（使用TB）能力。内旋和前伸在鹰的飞行行为中可能不太重要，但其捕食攻击行为可能需要维持一个较大的TB来进行制动和控制失速，因为它启动攻击行为。
