Hi Terry try this site to get help for your injured pidge ... http://helpwildlife.co.uk/
No real helpful advice about cats though unless you try pepper spray along the fence top & water pistol every cat you see to deter safely!
2013 photos & vids here
eff37 on Flickr
Would pepper spray cause serious injuries to cats if it goes in nostrils or eyes? Not sure.
Terry it would help if you could upload a photo of your fence so we can see the surroundings. In the meantime here is some ideas. Vaseline works perfectly well as does the 'thief repellent' paint for pipes they sell at B&Q.
My Gallery
"Any glimpse into the life of an animal quickens our own and makes it so much the larger and better in every way." John Muir
More research leads me to not like the pepper on the fence theory as it can be very irritating to cats' eyes ... likewise I would question the use of coating bird seed to deter Squirrels as it could possibly irritate birds' eyes also especially if too much is used! So scrub that & keep liberally spraying the little perishers with water!
The problem is,the birds sit on the fence facing inwards to the garden and then the cat come up from behind?
Do you have any flowerbeds near the fence? I am currently growing rambling rose along a low fence to prevent cat activity. In the meantime I installed some strips of large plastic spikes, which deters cats and birds alike. Once the rose has spread sufficiently I will remove the spikes. Maybe it is worth preventing the birds from landing by installing large spikes, or if you are putting out seed, put the seed in a different location so that the birds approach from a different direction. I also did that a year or so back because the hundred or so Sparrows were leaving too many 'messages' on my neighbours side of the fence!
Unicum arbustum haud alit duos erithacos
(One bush does not shelter two Robins)
Zenodotus (3rd Century B.C.)