Abstract
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 a 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. Three-dimensional 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 6 mm 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.
Highlights
Flying animals have an astonishing ability to negotiate obstacles and narrow openings when flying in complex environments such as forest habitats
When flying in an open habitat, impaired by having to fly in a complex and cluttered one? Previous work 2 on birds flying past obstacles and through narrow openings have focused on several different aspects including the visual processing of obstacles along the flight path [1,2], the ability of the bird to assess the width of the gap in relation to its own wingspan [3,4], the bird’s ability to make split-second decision which gap to use if presented with two different widths [5] or what route to choose through an obstacle course [6]
We see that as long as the gap is wider than the wingspan, the bird flies with the same flight speed, but when the gap width is lower than the span, horizontal speed is reduced with reducing gap width while a small upward vertical speed results in a slight gain in altitude before the gap
Summary
Flying animals have an astonishing ability to negotiate obstacles and narrow openings when flying in complex environments such as forest habitats. Previous work 2 on birds flying past obstacles and through narrow openings have focused on several different aspects including the visual processing of obstacles along the flight path [1,2], the ability of the bird to assess the width of the gap in relation to its own wingspan [3,4], the bird’s ability to make split-second decision which gap to use if presented with two different widths [5] or what route to choose through an obstacle course [6] These studies have revealed a lot about how the birds are capable of flying through complex environments
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