My apologies for the egregious lack of polar bears in this game. I actually coded a polar bear but by some astonishing blunder I haven't included one in any of the levels. It can walk safely on ice like the penguin, but is "strong" so it can push multiple crates.
I hope you've enjoyed the game all the same, despite its outrageous dearth of arctic ursine predators. No promises, but I'd like to do a level pack update for Zookoban at some point, which would definitely address this defect.