Why are bird flight diverters shaped like a spiral?

Question

I was out walking and saw these strange looking spirals on some power lines.

When I got home I did some research and discovered that they are to prevent birds form hitting the power lines, mainly used in conservation areas. I found this interesting study about which types of flight diverter are the most effective at preventing bird collisions. It mentions a few other types of diverter (plate, swivel, sphere), but the spiral seems to be the preferred shape to experiment with (big vs small) and the reason for this is not explained.

I can understand that a spiral wire has a good visibility to weight ratio, but is this the only reason for the shape? Would there be any current transmitted through (or induced in) the spiral, and would this shape help in any way to prevent any negative effects this might have? Or am I just thinking that there is an electrical reason because the spirals remind me of magnetic field lines, when really that's nothing to do with it?

Jon W · Answer

Originally the spiral shaped devices were fitted to the earth wires on top of pylons as vibration dampers (the very top single wire on pylons is the earth wire). It was however noted that they also had the effect of discouraging birds from landing on the wires. Therefore the spiral bird diverters can be used as dual purpose devices. Keeping birds away and effectively managing vibration issues on lines in particularly windy areas. Although these days newer weighted vibration dampers are used on most problem lines.

They use spirals so that during periods of vibration the spiral will bounce around and hit the wire and disrupt any vibration patterns (specifically they were designed to prevent a vibration type called aeolian vibration) in the line. The weighted dampers can't do that. Generally they use the weighted dampers on thicker cables and spirals on thinner ones.

Why are bird flight diverters shaped like a spiral?

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