How can I make my koalas happy?

I'm trying to get the Steam achievement for all animals with 99% happiness in Wildlife Park on PC. I'm almost there, but I just can't get my Koalas happy.

I've filled their habitat with eucalyptus and climbing platforms, but they keep telling me that they "urgently" want to climb and have no opportunities. I even removed the leaf bins, to force them to get their own food from the trees (under the theory that this would force them to climb), but no luck.

I actually saw one of the koalas climb up the climbing platform once, but now they're all just shuffling about on the ground and making sad meeping noises.

How can I get my koalas happy? Other than the climbing thing, they're all set, but they're ignoring my climbing platforms. Is there some other accessory I should be using for them to climb? Should I maybe build cliffs for them to climb up?

_{(I apologize if this question is already asked somewhere. It's fantastically hard to google a game named "Wildlife Park"....)}

Solution 1:

Koalas will, for reasons unknown, ignore the climbing platforms. The only opportunities they have to climb are, therefore, a cliff.

A cliff must have clearance of two levels for it to be considered a climb target. In your koala enclosure, a single 1x1 2-block high cliff is sufficient to satisfy your koalas (for a minimum-size and one koala den; larger enclosures and more dens may require multiple cliffs.)