Are you serious? I think 3 of the biggest zoos of the world are in Europe. Have you a better list to representative which animals lifes in captivity?
Tom, not really my intention to derailed this thread any further, or to try lecturing you about your statement. I have been involved with the zoo world for decades now, visited over 400 zoos worldwide, had lengthily discussions with actual authorities in this matter and lived for years in Europe as well as the U.S working in zoo planning and design projects in both continents. When one refers to the biggest zoos in the world, then that is an extremely subjective discussion, since we can be taking into consideration, the number of species within the collection, attendance and popularity of the institutions, their progressive and innovative approach when it comes to conservation, breeding etc, the quality of the exhibits and the money that has been spent to create groundbreaking thematic areas. Someone could also be simply referring to the actual land size of the zoo, even though It is my believe this is not what you meant.
Now let us backtrack for a minute, your statement reads
"Are you serious? I think 3 of the biggest zoos of the world are in Europe. Have you a better list to representative which animals lifes in captivity?"
If you take all of the categories listed above as a point of reference (it is not a matter of you taking them or not, it is just the only factual way we can measure their standing) Europe actually does not rank as high as you might otherwise think, in fact with the exception of a couple of categories, they really do not rank high at all. When it comes to the greatest number of species being displayed in a zoo, Zoo Berlin still carries the torch, as their collection together with the Tierpark Berlin, are still some of the largest in the Planet. However since Zoo Berlin has gradually being reducing their collection to make way for higher quality exhibitions, even this category will go away. A much similar situation to the San Diego Zoo, and how they have been reducing their extensive collection for years now. Let us also take into account, that the large number of species within the Berlin Zoo is in great numbers aided by their large aquarium on zoo grounds. When we look at attendance, popularity and revenue being brought in, then it gets really interesting because this ranges significantly depending on what zoos data you are inspecting, the general consensus is that when you look at a general picture the U.S ranks ahead. As far as progressive, innovative and groundbreaking approaches when it comes to conservation and so on, there is no question that the U.S also has a significant lead here. Now comes the biggest differentiation between zoos in Europe and U.S zoological institutions, quality of the exhibits, and zoos overall. Being involved in some of the biggest and most expensive zoological projects in Europe, I can tell you first hand, that this is a no contest, not even close, the U.S spends more in zoo exhibits than all other countries combined, and that is a fact.
I will tell you this, there is a large contender that has been steadily cementing its position as the premier zoological destination in the world and that is the Mandai Park complex in Singapore, with the addition of the nature reserve and new bird park annexed to the already existing Zoo, night safari and river safari, it would be hard not to place this destination at the very top of the list. So if someone makes the statement, Europe has the biggest zoo in the world by way of species count (Berlin Zoo) then you would be correct, if we took all the insects and small fish species away, then it would be the Henry Doorly Zoo with 963 species. As an FYI the most expensive and ground breaking zoological exhibits in our planets history are located at the Bronx Zoo in NYC, until recently when San Diego Zoo opened their African Rocks exhibit at a cost of 68 million dollars, as a point of reference Paris built their entire Zoological Park of Paris at a cost of 181 million. The most expensive, innovative and groundbreaking zoo in the world at this moment is still Disney's Animal Kingdom.
I must add, that this is not a poor reflection of Europe's outstanding zoological institutions, as the majority of them combined with their long lasting history are exceptional. Some of my favorites zoos in the world are in Europe, since I appreciate their legacies, and character found within their historical grounds. Many Zoos in Europe are also progressive, and have state of the art Zoo exhibits, the Masoala Rainforest at the Zurich Zoo and Gondwanaland at Zoo Leipzig come to mind. One of the projects that I have been most proud of working on during my entire career was Valencia Bioparc in Spain, during my time with Rainforest, as well as Fuengirola Bioparc a much smaller thematic and fully immersive zoo that was planned and built from the ground up over a vastly outdated institution.