how can I prevent birds to come in my yard?

Put a bell on each cat so that the birds can become alert whenever a cat approach them.

Another thing, buy those fake owls that they sell at hardware stores. Put them around your yard and hopefully they will deter birds from entering your yard.

-- PA

Scarecrows (including fake owls and pinwheel/windmill toys) don't scare off birds for long. Putting a bell collar on your cat may or may not work. I had a friend who tried this and he said the birds paid the noise no mind and the bell just drove the cat crazy.

You can also try removing anything in your yard that is appealing to a bird. Stop feeding them if you do and remove any sources of water. If your cats habitually use the same cover to stalk the birds, try removing this as well.

Of course, you can always keep your cats inside, which may be the best options for all parties involved. If this is not possible, maybe you could build an outdoor cage or buy a dog kennel so your cats can still enjoy their outdoor time without harming the wildlife.

put a bell on the cat's collar to alert the birds.

scare crow