Since modern Berlin comes from the merger of two cities of different states, namely, the capital of the GDR and the administrative subject of Germany, there are two central zoos in it. This one is from the East, from the GDR. It's not as well advertised, but it occupies a large area. You feel more free in it, like on an exotic walk, rather than in a museum (it seems that pets too), however, its visit depends more on the weather.
Some pets, like peacocks or mandarin ducks, can often be seen outside the zoo.