Doing a little research, I think I have discovered a way to save money on visiting these places if there are two (maybe more) people going.

Purchased online in advance, entrance to the zoo or the wild animal park is $74 each, or $148 for 2. If you want to go to each place on a different day, two two=visit passes would cost $252.

But a "wldlife protector premium" membership costs $169 (and $152.10 for seniors);. It gets the member unlimited admissions to both parks and free parking at the Wild Animal park. Plus you get a free one-day entry for a guest, and two additional 50% off coupons for guests. Thus it's pretty much a wash or small savings on a one day visit for two people but a nice on two two-day visits. And the member also gets free tram tours, bus tours, and 10% off at all shops, plus a few other privileges. Additionally, the card is good for a year.

A lot of places have interesting tradeoffs between admission and membership, but this deal seems to be one of the few that is breakeven on just a single day visit for two people and then gets way better fast after that.