Bird In A Cage

Fed up with the rooks and jackdaws pilfering all the bird food that I put out each day I've bought some small bird friendly feeding devices. The fat ball container is rather on the large size. It works well though, but I'm a little worried that if they eat too much the sparrows may not be able to get out again!

As I write this a rook is swinging on top of the cage. I guess it may just be a matter of time before they work out how to break in!