蜂鸟可谓鸟类家族中的杂技演员——它们每秒钟至少拍打翅膀45次,并且能够盘旋着前进、后退,甚至倒置。然而,蜂鸟的空中行动非常消耗能量,因此它们每天至少要大吃大喝一次花蜜,即便在恶劣的天气中也是如此,否则这种小鸟便会死去。
那么当一场暴风雨来临之际,在它们被重量达到自身体重35%的雨滴狠狠敲打时,这些蜂鸟究竟是如何过活的呢?根据日前在线发表于英国《皇家学会学报B》(Proceedings of the Royal Society B: Biological Sciences)上的一项研究,它们干得很出色。
科学家之前在今年夏季的早些时候也曾对蚊子进行过类似的试验。在这项研究中,美国加利福尼亚大学伯克利分校的动物学家Victor Manuel Ortega-Jimenez和Robert Dudley将5只雄性安娜蜂鸟(Calypte anna)在实验室中置于小雨、中雨和大雨的环境中,并利用高速录像机分析了它们的飞行响应。
研究人员发现,这些小鸟几乎没有受到小雨和中雨的影响,但它们在大雨中不得不采取一种完全不同的姿势以确保对飞行的控制,蜂鸟会水平地转移自己的身体和尾巴,并更迅速地拍打翅膀,同时减少翅膀运动的角度。
研究人员发现,蜂鸟位置的变化最初是似是而非的,这是因为每只蜂鸟都会更多地将它们的背部暴露在正在到来的雨水中。
然而,更进一步的研究显示,这种姿势或许减少了雨滴击中蜂鸟翅膀的总量,从而使其能够更加稳定地停留在空中。
研究人员同时发现,蜂鸟抗水的羽毛吸收了倾盆大雨带来的50%的冲击,从而帮助它们在飞行中保持轻盈,并且无论在何种天气情况下都能够掌控身体。
蜂鸟是雨燕目蜂鸟科约600种动物的统称,是世界上已知最小的鸟类。蜂鸟因拍打翅膀的嗡嗡声而得名。蜂鸟是唯一可以向后飞行的鸟。蜂鸟也可以在空中悬停以及向左和向右飞。(生物谷Bioon.com)
doi:10.1098/rspb.2012.1285
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Flying in the rain: hovering performance of Anna's hummingbirds under varied precipitation
Victor Manuel Ortega-Jimenez1,* and Robert Dudley1,2
Flight in rain represents a greater challenge for smaller animals because the relative effects of water loading and drop impact are greater at reduced scales given the increased ratios of surface area to mass. Nevertheless, it is well known that small volant taxa such as hummingbirds can continue foraging even in extreme precipitation. Here, we evaluated the effect of four rain intensities (i.e. zero, light, moderate and heavy) on the hovering performance of Anna's hummingbirds (Calypte anna) under laboratory conditions. Light-to-moderate rain had only a marginal effect on flight kinematics; wingbeat frequency of individuals in moderate rain was reduced by 7 per cent relative to control conditions. By contrast, birds hovering in heavy rain adopted more horizontal body and tail positions, and also increased wingbeat frequency substantially, while reducing stroke amplitude when compared with control conditions. The ratio between peak forces produced by single drops on a wing and on a solid surface suggests that feathers can absorb associated impact forces by up to approximately 50 per cent. Remarkably, hummingbirds hovered well even under heavy precipitation (i.e. 270 mm h?1) with no apparent loss of control, although mechanical power output assuming perfect and zero storage of elastic energy was estimated to be about 9 and 57 per cent higher, respectively, compared with normal hovering.