First of all, thanks must go out to both
@Arek and
@Shorts, a couple of true zoo enthusiasts who I've been told have a massive amount of zoo literature between them. That would include zoo maps, guidebooks, annual reports, postcards and now a copy of
America's Top 100 Zoos & Aquariums. I am thrilled to have been a co-author of such a splendid book that was worth many years of hard work, editing and rewrites. Thanks for the kind words guys!
Also, Tim recently had a reply from the legendary Bent Jorgensen, who founded the magazine
International Zoo News way back in February 1951...when Bent was only 17 years old! In his message to Tim, Bent was incredibly kind and his words are ones that I'm going to save and treasure. He certainly knows zoos, as apart from producing the magazine for decades he was the Director of Copenhagen Zoo from 1979 to 1994.
On the subject of a book titled
Europe's Top 100 Zoos & Aquariums, at the moment there is ZERO chance of Tim and I working on such a magnum opus. Trust me, I've brought it up with him on a couple of occasions already!

Our American zoo book has been so well received that I'm convinced a European version would sell TWICE the number of copies, but for now it is not an option. I want to make that crystal clear, as I've had a lot of people suggest it to me and European zoo nerds are so far above North American zoo enthusiasts in terms of collecting zoo-themed ephemera that I believe a Brown/Richardson European zoo book would be a major hit. However, we just completed 5 years of on-again, off-again work on the American zoo book and my next big 'Snowleopard Road Trip' is tentatively set for 2022 and then we'll see after that. Tim has probably already visited 95% of all the 'best' zoos in Europe in his lifetime, but I'd need another big Euro trek to hit 50% of the best zoos on the continent and then I promised him that I'd start harassing him to write another book with me. We'll see...but for now it's a dead issue.
In terms of a European zoo book, at first I was inclined to agree with
@lintworm and the prospect of narrowing down Europe's zoos to a subjective 100 can seem intimidating. For the American zoo book we had approximately 800 'zoos' of all shapes and sizes but getting 100 for the USA book wasn't much of an issue. In Europe there are around 200 zoos just in France, another 200 in the United Kingdom, at least 100 in the Austria/Switzerland region, 500 or more in Germany, etc, etc, etc. The numbers are mind-boggling with a zoo seemingly around every corner and as ubiquitous as streetlamps.
BUT...looking at the last book from the much-maligned Anthony Sheridan, I can point to the fact that he has 115 zoo profiles in there and then 9 specialist zoos to make it 124 zoos profiled in his book. There are at least a dozen fairly obscure facilities selected by Sheridan and so narrowing down the list to 100 wouldn't be as difficult as perhaps first imagined.
Lastly, one factor with a European equivalent to
America's Top 100 Zoos & Aquariums is the scarcity of mega aquatic establishments. Tim and I came up with exactly 80 zoos and 20 aquariums for our USA book, but if someone was to write a book about Europe's collections then how many aquariums would make the final cut? There's Valencia, Lisbon, Copenhagen, maybe Moscow if we stretched things that far geographically, Genoa and Nausicaa in France. That's only 6 major aquariums, including the hard-to-get-to 'Moskvarium'. Any more really big ones that I'm missing? Loads of major European zoos have aquariums inside the grounds already and so stand-alone,
huge aquariums are a rarity.