Sort your guests by favourite animal then make an exhibit for them. Make only part of the exhibit viewable as the animal's privacy level will go red if there are to many people. Put a couple of donation boxes by the exhibit and you could put a tour in as well. People will enjoy their favourite animal and will donate lots of money, especially if they have babies. I will experiment and put some more info on this topic for everyone if no one else does before me.
I am now experimenting. I have 6 results so far. Over three months in the same exhibit and with one donation box, the ES animals receive this info:
Giant Sable Antelope - 76 Don. - $4, 384.68
African Wild Dog - 91 Don. - $7, 280.00
Markhor - 129 Don. - $7, 435.97
Gray Wolf - 135 Don. - $10, 631.71
Wolverine - 121 Don. - $8, 330.17
Scimitar Horned Oryx - 129 Don. - $4, 989.37
Fennec Fox - 139 Don. - $10, 942.51
Przewalski's Wild Horse - Don. - $