attendance, species count, number of rare species, conservation efforts, and adding new innovative and well made exhibits
Starting from this thread:
European zoo attendance the 5 biggest zoos attendance-wise would be Berlin, Moscow, Lyon, Munich and Pairi Daiza.
I think it's fair to say that Lyon is disqualified because it's really fairly small. Moscow on the other hand gets disqualified because its husbandry standards are quite clearly below those of Europe (as well as only marginally being part of Europe). Munich, whilst having a large attendance and good enclosures, loses out because it lacks the species count, rare species, and innovative exhibits.
That would then make my somewhat-but-not-really objective big 5: Berlin, Pairi Daiza, Vienna, Chester and Leipzig. I think that's not a bad list - all are world-class zoos with comprehensive collections and a decent amount of rarities. Conservation efforts vary, but as far as I know Vienna, Chester and Leipzig make significant contributions, and I suppose both Berlin and PD also contribute a fair bit.
However, personally, I don't like PD very much. I'd much rather replace it with a zoo that has everything PD has, but has more innovative exhibits and a higher husbandry standard. I suggest looking a bit lower on the list, at either Zurich or Burgers. These two are more deserving of PD's spot, I think. Between those two, Zurich takes the cake with a larger and more comprehensive collection, and a larger attendance (and also a larger contribution to conservation?).
So my final objective-but-not-really Big 5 list would be:
- Zoo Berlin
- Tiergarten Schönbrunn (Vienna)
- Chester Zoo
- Zoo Leipzig
- Zoo Zürich