I have two semi-feral outside cats. I feed them, and they thank me by keeping other cats and those having kittens out of my yard. They also catch mice, voles, moles, and shrews. And occasionally birds.
Today I finished blocking the area around one of my bird feeder stations as Alice has been using it as a buffet.
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The feeder area is now completely enclosed with fencing. Most is about 36" high, but the fencing I used to finish is about 16" high. Technically the cats can leap over it, but it should spoil the element of surprise, and give the birds a better chance.
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I also placed a bent section of wire fence outside the barrier, making another difficulty for the cats to overcome.