James, Personally I would replace the whole wire rather than repair with electrical tape. A few meters of wire would be a couple of quid at the most. You can buy armoured cable that they wouldn't be able to chew through, but the cheapest option would be as other suggested, use small plastic tubes ( called conduit ). They come in various sizes and shapes, or you could use a bit of water hose pipe! Will depend on how asthethically pleasing you want it.
Conduit (plastic tube) can be painted, but must be rubbed with sandpaper (to key the surface) then an oil based paint used first. Or it will just run straignt off.
I ordered a UV light from Scarlett and this was something that concerned me from the start, however, whilst lounging in the bath I noticed the shower hose and had a eureka moment; I saw the shower hose.
So yesterday I went to the pound shop and bought a shower hose, my light arrived today, along with various other supplies, and this is the result:
an armoured cable.
Points to note:
In order to fit this you need to remove the entire light fitting, the switch is a sealed unit so cannot be removed safely.
As well as being confident in what you are doing you have to accept that you are certainly invalidating the guarantee.
Although very strong you will still need to watch the birds carefully, mine have so far shown no interest in it but do seem to enjoy their new illumination.
As the hose probably contains zinc I'm also going to place a length of split plastic pipe over the cable.
With the above provisos I think I've found a simple, safe, effective and cheap solution but if you are tempted to try it be very careful and only proceed if you have basic electrical safety knowledge.