A magpie raiding the sunflower seeds

I'm rather disconcerted to have found out why the sunflower feeder seems to be emptying twice as fast as usual. I sat in the cabin to have a cup of tea, listen to some music and watch with my camera. A variety of birds appeared including a goldfinch, greenfinch, bullfinches, many blue tits and a lone nuthatch.

But when this magpie landed on the patio table it rather shocked me when it flew straight onto this supposedly squirrel-proof feeder, and proceeded to dip into the feed holes. I stayed there for quite some time and ate countless seeds. The design of the feeder is such that when an animal heavier than a small bird lands on the cage it slides down the outer cage to cover over the feed holes.

The magpie has learnt that if it sticks its foot in one of the holes it can stop the sliding cage from dropping down, and can feed forever, with its long beak able to reach through even a small hole if necessary. Oh dear. I'm going to have to think up some equally clever foil to this pest. The small birds consume at least one of these tubes filled with de-shelled sunflower seeds each day, but with the magpie they could empty within an hour. We have a lot of magpies.