Data for: Flying through gaps – How does a bird deal with the problem and what costs are there?

Animals flying in the wild often show remarkable abilities to negotiate
obstacles and narrow openings in complex environments. Impressive as these
abilities are, this must result in costs in terms of impaired flight
performance. In this study, I used a budgerigar as model for studying
these costs. The bird was filmed in stereo when flying through a wide
range of gap widths from well above wingspan down to a mere 1/4 of
wingspan. 3D flight trajectories were acquired and speed, wingbeat
frequency and accelerations/decelerations were calculated. The bird used
two different wing-postures to get through the gaps and could use very
small safety margins (down to 6mm on either side) but preferred to use
larger when gap width allowed. When gaps were smaller than wingspan flight
speed was reduced with reducing gap width down to half for the smallest
and wingbeat frequency was increased. I conclude that flying through gaps
potentially comes with multiple types of cost to a bird of which the main
may be: i) reduced flight speed increases the flight duration and hence
the energy consumption to get from point A to B, ii) the underlying
U-shaped speed to power relationship means further cost from reduced
flight speed, and associated with it iii) elevated wingbeat frequency
includes a third direct cost.

野外飞行的动物往往展现出卓越的能力，可在复杂环境中规避障碍物并穿越狭窄通道。尽管这些能力令人惊叹，但其必然会带来飞行性能受损相关的代价。
本研究以虎皮鹦鹉（budgerigar）为模型，探究此类飞行代价。实验中，该鹦鹉在穿越跨度范围从远大于翼展直至仅为翼展1/4的各类间隙时，以立体摄像方式进行记录。
研究获取了其三维飞行轨迹，并计算了飞行速度、振翅频率以及加/减速度等参数。该鹦鹉可通过两种不同的翼部姿态穿越间隙，其安全裕度可低至两侧仅余6毫米，但在间隙宽度允许时更倾向于采用更大的裕度。
当间隙小于翼展时，飞行速度随间隙宽度减小而降低，最小间隙下速度可降至原速的一半，同时振翅频率升高。
本研究结论表明，穿越间隙的飞行行为会给鸟类带来多类代价，其中主要代价包括：其一，飞行速度降低会延长飞行时长，进而增加从A点抵达B点的能量消耗；其二，鸟类的速度-功率呈U型关系，飞行速度降低会进一步带来额外能耗；其三，振翅频率升高构成第三项直接代价。