Just remembered - I started cutting the mesh off years ago. I found a group of jackdaws watching for when the balls had become small enough they could pull them out of the feeder. One'd grab the mesh and hang on, beating its' wings until it pulled the fat ball through a gap! They'd all set about it and then start on another.
I think magpies fly off with them as well - I've seen one pecking at something on a neighbour's ridge tile and then the mesh falling into his gutter.
The mesh nets are just too dangerous.