My Neighbour has over 100 cat...........Yes i did type it right over 100. Last summer the little buggers got every last chick and duckling that we hatched and also all of our quails. We doubled the height of our perimeter fence around the land and property to 2 meters high and the fence to the pen to 2 meters. Still didn´t stop them.
We spoke to the local police here as she has so many and they are not micro-chipped ( which is law here) They gave me a humane cat trap to place in the garden and then when we had a few we would call them back and they would take them to the dog and cat pound.
I caught cats i didn´t even know came in the garden. We caught on average 20 cats a day.
She was FUMING

with us. Every time she wanted them back she had to pay30€ a cat. Oh and had to have them chipped, another 36€ on top.
Funny enough after a month of this happening we didn´t see any more cats in the garden. She now keeps them ALL inside. every now and then we will see them out and we get the trap again and catch one or two and she shuts them up again.
For me this was a last resort but i have to say it was the best thing EVER. She is due to move in the next 3 months and will be taking the cats with her. The new buyers came and introduced themselves the other day and they have 8 dogs but no cats. I can put up with barking as that wont kill our spring babies. Also they are going to fence all their land. (result)
I know this doesn´t really help you much as you too have cats but i just thought i would share it with you.
For me i think this years babies will be safe. oh and just in case anyone is thinking why didn´t we put a top on there run, well its because its an area of 1000 square meters that they have with very large olive trees in. They are very lucky free range birds :yiipchick