Hey leheng and welcome to Berlin! It would be great to increase the level of detail of the Tierpark here. So I'm absolutely in favour of adding the animal areas. According to the wiki (https://wiki.openstreetmap.org/wiki/Tag:attraction%3Danimal) and as seen on many other places with animals, we should use "name" for indicating which animals are there (we should use the german names, but I or other mappers can add them later).

Are you just visiting Berlin or living here now? Because if you are here for longer, we can give you many tips for using a lot of background layers and aerial imagery that are provided on a yearly base and in a OSM conform license from the Berlin government and can therefor be used for mapping (for example to map the animal enclosures as areas in there exact extend :)

Best, Alex