The San Diego Wild Animalpark is indeed a good zoo, because the animal welfare is pretty good-hoofstock in big herds in big encloures and they never put into small stalls like in europe--they don't know what a barn is...european zoos have to learn so much how to keep antelopes,rhinos, giraffes, and zebras, and most rhinos in germany have never seen a mud hole in their life, and elephants is only allowed taking a bath at a special time, so visitors can watch it...
San Diego Zoo is indeed on of the worlds zoo with a large "collection", but luckily, they reduce it to give the other animals more space.