There is that as well and maybe it's only PR spin but I've been told more than once that they are keen to preserve the feel of the place and that kids enjoy jumping in muddy puddles. I'm not sure that the visitors wearing brand new white trainers feel as enthusiastic as the children do about mud but if you promote the zoo as a day out in the countryside, they can't complain too much.Another reason for not tarmaccing paths, is the cost of probably over £100 per square meter to do so?