Embedded nodes and views
I would advise node References and Entity Views Attachment 


Create 2 content types: 1) Zoo - 2) Animals
Animals has a "Node reference" to a Zoo
Create 2 views: 1) Zoo - 2) Animals -  Attach entity contents by relating them and contextual filters on nid


This way you can create Zoo pages [node] with all the animals in the zoo
On the animal pages [node], you can show which zoo(s) the animal belongs

You can also create pretty overview [views] pages