Thank you for that; it is the first time I have a seen a 'multiplier' actually explained. Here we have a simpler formula - because an annual pass costs three times the day entry fee, we count each purchase as three visits because that is what it is worth, financially. In reality most such purchasers use their tickets more than three times, so our actual footfall is higher than that recorded.
In a few months, this thread will be 4 years old and a lot has occurred in those years! It would be interesting for @lintworm to analyze the data at this point in time, now that everywhere is back to full capacity and airports are bursting at the seams. Unfortunately, after 60 years of operation, the International Zoo Yearbook is now an extinct publication and that was once a valuable source of information. I'm sure that the list of 41 zoos with a minimum of 1 million annual visitors won't have changed a great deal, but it would still be intriguing to see the little shuffles here and there. One major change would be that of Beauval Zoo, which is apparently going to hit 2 million visitors this year and then has one of Europe's largest aviaries opening in 2023 that will boost numbers even higher. Beauval and Pairi Daiza seem destined to be #1 and #2 in the future, locked in a battle for popularity. (It's interesting to note that in the United States there is a total of approximately 55 zoos and aquariums with a minimum of 1 million annual visitors. Around 20 of those receive 2 million annual visitors or more.)
Wait till year 2022 is closed and most large zoos announce their figures, patience. However, stated advantage in attendance of the US zoos compared to Europe is interesting and hopefully we will catch up a little bit this time.
I think that the attendance advantage of American zoos has a lot to do with geography. Most major zoos are either located in metropolises with more than 1 million inhabitants (over 50 and even 35 with a metro population of over 2 million) or in popular holiday destinations. So each of the major zoos either has a huge base population for which it is the closest (and often only nearby) major zoo or plenty of holiday folk or a combination. For example Nashville has a metro area of 2.2 million people and the nearest large zoo that is not Nashville would be a very significant drive. Looking to Europe there are often multiple good zoos within short driving distance. A more "American" situation is visible in S Germany where all four major zoos easily pass the 1 million visitor mark yearly. Partly because outside the 4 major metropolitan areas (Munich, Nuremberg, Stuttgart and Karlsruhe) there are very few major zoos and cities and population densities on the countryside are low. Apart from these 4, it is only Heidelberg and Augsburg that have a reasonably well established zoo. (Heidelberg is an interesting case, being in the Mannheim-Heidelberg-Ludwigshafen metropolitan area, which has a high population density, but is relatively close to Karlsruhe, Stuttgart and Frankfurt, so might not have the power for a major zoo on its own). What some US zoos do better than Europe is that they in themselves have become a holiday destination like Animal Kingdom, San Diego Zoo and to a lesser degree also Omaha. The Sea Worlds and Disney's also profit from the theme park - zoo combination, which is also a clear indicator for higher attendance in Europe.
