Paskins Keith E, Bowyer Adrian, Megill William M, Scheibe John S
Centre for Biomimetic and Natural Technologies, Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, UK.
J Exp Biol. 2007 Apr;210(Pt 8):1413-23. doi: 10.1242/jeb.02747.
Flying squirrels are well known for their ability to glide between trees at the top of a forest canopy. We present experimental performance and behavioural evidence that flight in flying squirrels may have evolved out of a need to control landing forces. Northern flying squirrels were filmed jumping from a horizontal branch to a much larger vertical pole. These were both slightly compliant (less than 1.9 mm N(-1)), and instrumented using strain gauges so that forces could be measured. Take-off and landing forces were both positively correlated with horizontal range between 0.5 and 2.5 m (r=0.355 and r=0.811, respectively, P<0.05), but not significantly different to each other at each range tested. Take-off forces ranged from 1 to 10 bodyweights, and landing forces were between 3 and 10 bodyweights. Glide angles increased rapidly with horizontal range, approaching 45 degrees at 3 m, above which they gradually decreased, suggesting that northern flying squirrels are optimised for long distance travel. We show that northern flying squirrels initiate full gliding posture at ranges of less than 1 m, without landing any higher than an equivalent ballistic projectile. However, this gliding posture enables them to pitch upwards, potentially stalling the wing, and spreads the landing reaction force over all four extended limbs. At steeper approach angles of close to 45 degrees , flying squirrels were unable to pitch up sufficiently and landed forelimbs first, consequently sustaining higher impact forces. We investigate four hypotheses to explain the origin of flight in these animals and conclude that the need to reduce landing impact forces was most likely to have stimulated the development of aerial control in flying squirrels.
鼯鼠以其在森林树冠顶部的树木之间滑翔的能力而闻名。我们提供了实验性能和行为证据，表明鼯鼠的飞行可能是出于控制着陆力的需要而进化而来的。对北方鼯鼠从水平树枝跳到一根大得多的垂直杆子上的过程进行了拍摄。这根杆子都有一定的柔韧性（小于1.9毫米/牛顿），并使用应变片进行了测量，以便能够测量力。起飞力和着陆力与0.5至2.5米之间的水平距离均呈正相关（分别为r = 0.355和r = 0.811，P < 0.05），但在每个测试距离下两者之间没有显著差异。起飞力范围为1至10倍体重，着陆力在3至10倍体重之间。滑翔角度随着水平距离迅速增加，在3米处接近45度，超过该距离后逐渐减小，这表明北方鼯鼠在长距离飞行方面具有优化特性。我们发现北方鼯鼠在距离小于1米时就开始采用完全滑翔姿势，着陆高度不会高于同等弹道抛射体。然而，这种滑翔姿势使它们能够向上倾斜，可能使翅膀失速，并将着陆反作用力分散到所有四个伸展的肢体上。在接近45度的更陡接近角度下，鼯鼠无法充分向上倾斜，前肢先着地，因此承受更高的冲击力。我们研究了四种假说来解释这些动物飞行的起源，并得出结论，减少着陆冲击力的需求最有可能刺激了鼯鼠空中控制能力的发展。
