The terrariums in the bird islands for example, whilst being pathetic for the Siberian Flying Squirrel, are totally adequate for the mice that call most of them home
The collection might change quickly, but apart from the Flying squirrel, quite some tanks kept Garden dormouse based on memory and only few had Lemming of Mice (for which it is much better suited, though still on the small side imo.)
I sometimes feel I am a bit harsh on Plzen, that may have had partly to do with my mood when visiting it and the expectations I had of it beforehand. As Plzen was basically always praised here, the bar was set higher than it could fulfil. It also didn't help that it wasn't the best weather and there was a heavy metal festival going on in the Amphitheatre next door. The day prior I spent in Nuremberg with perfect weather and no heavy metal. There is hardly a zoo that can be more contrasting to Plzen and that visit was one of my most pleasant zoo visits in years. So Plzen had a lot to lose, though Prague the following day managed to compensate quite a lot.