Watanuki Yutaka, Wanless Sarah, Harris Mike, Lovvorn James R, Miyazaki Masamine, Tanaka Hideji, Sato Katsufumi
Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho 3-1-1, Hakodate, 041-8611, Japan.
J Exp Biol. 2006 Apr;209(Pt 7):1217-30. doi: 10.1242/jeb.02128.
In diving birds, the volume and resulting buoyancy of air spaces changes with dive depth, and hydrodynamic drag varies with swim speed. These factors are important in the dive patterns and locomotion of alcids that use their wings both for aerial flight and underwater swimming and of penguins that use their wings only for swimming. Using small data-loggers on free-ranging birds diving to 20-30 m depth, we measured depth at 1 Hz and surge and heave accelerations at 32-64 Hz of four species of alcids (0.6-1.0 kg mass) and the smallest penguin species (1.2 kg). Low- and high-frequency components of the fluctuation of acceleration yielded estimates of body angles and stroke frequencies, respectively. Swim speed was estimated from body angle and rate of depth change. Brünnich's (Uria lomvia) and common (Uria aalge) guillemots descended almost vertically, whereas descent of razorbills (Alca torda), rhinoceros auklets (Cerorhinca monocerata) and little penguins (Eudyptula minor) was more oblique. For all species, swim speed during descent was within a relatively narrow range. Above depths of 20-30 m, where they were all positively buoyant, all species ascended without wing stroking. During descent, little penguins made forward accelerations on both the upstroke and downstroke regardless of dive depth. By contrast, descending alcids produced forward accelerations on both upstroke and downstroke at depths of <10 m but mainly on the downstroke at greater depths; this change seemed to correspond to the decrease of buoyancy with increasing depth. The magnitude of surge (forward) acceleration during downstrokes was smaller, and that during upstrokes greater, in little penguins than in alcids. This pattern presumably reflected the proportionally greater mass of upstroke muscles in penguins compared with alcids and may allow little penguins to swim at less variable instantaneous speeds.
在潜水鸟类中，气腔的体积及由此产生的浮力会随潜水深度而变化，流体动力阻力则随游泳速度而变化。这些因素对于海雀和企鹅的潜水模式及运动方式很重要，海雀既能用翅膀进行空中飞行，也能在水下游泳，而企鹅仅用翅膀游泳。我们在自由放养、潜入20至30米深度的鸟类身上使用小型数据记录器，测量了四种海雀（体重0.6至1.0千克）和最小的企鹅物种（体重1.2千克）的深度（1赫兹）以及纵荡和垂荡加速度（32至64赫兹）。加速度波动的低频和高频分量分别得出了身体角度和划水频率的估计值。游泳速度是根据身体角度和深度变化率估算出来的。厚嘴海鸦（乌燕鸥）和普通海鸦（海鸦）几乎垂直下降，而刀嘴海雀（刀嘴海雀）、角嘴海雀（角嘴海雀）和小企鹅（小企鹅）的下降则更为倾斜。对于所有物种而言，下降过程中的游泳速度都在相对较窄的范围内。在20至30米以上的深度，它们都具有正浮力，所有物种都无需划动翅膀就能上升。在下降过程中，无论潜水深度如何。小企鹅在向上划水和向下划水时都会产生向前加速度。相比之下，下降的海雀在深度小于10米时向上划水和向下划水时都会产生向前加速度，但在更深的深度主要是在向下划水时产生；这种变化似乎与随着深度增加浮力减小相对应。小企鹅向下划水时纵荡（向前）加速度的幅度比海雀小，向上划水时则比海雀大。这种模式可能反映了与海雀相比，企鹅向上划水肌肉的质量比例更大，并且可能使小企鹅能够以更稳定的瞬时速度游泳。
