Sunday 23 August 2020

Effect of nest box width on wing bending

A swift's wing length is about 170mm, thus any box with a minimum dimension less than 170mm will require the swift to bend its wings in order to turn. This post is a brief analysis of just how much a wing needs to bend for a range of box widths.

A number of nest boxes on the market have a minimum dimension of 100mm, which requires a wing to bend over 180° in order for the bird to turn.

The following charts illustrate the relationship between. box width and degree of bending. These are calculated with an idealized assumption that a straight wing would bend into a circular arc. Of course, most of the bending and wear will be concentrated nearer the wing tip which might be worse than it being uniformly distributed along the wing length.

Swifts will nest in boxes 10cm wide, but the wear to their wingtips after a whole season of turning in such boxes is unknown.

Relationship between box width and bend angle
The range of shapes for different box widths. All of these lines are the same length, 170mm.

Thanks are due to Mark Smyth for these videos showing a Swift turning in a 10cm wide nest box:


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