In an announcement made on the ZooMumba homepage, publishers Bigpoint have addressed some concerns of players, one of them being the wish for more space. The new feature to help address this problem is the Zoo-O-Meter.
The Zoo-O-Meter will consider the values of your Main and Hidden Zoo, allowing you to better manage the animals in both. For example, if you have an animal in your Main Zoo, you no longer need it in your Hidden Zoo anymore to achieve full popularity. That means you save space!
On top of that, the problem of having different income on both entrance buildings in ZooMumba will also be fixed. Keep your eyes open for more coming in the near future.
Source: Game homepage