Very sad to hear - and I agree it is instinct - however I followed the technological line and haven't seen any pesky cats in my garden since the installation. Yes it costs abit of money, but I can safely say that all the birds in my garden are protected - and i swear that they have even learnt that the cats don't come in.
I bought these
Catwatch cat deterrent.
One to cover each side of the garden - so two. They are from the RPSB shop and don't affect the birds at all.
Hope this helps
Steve