There follows a discussion on how The Zoo Guide Directory has dated the guides in its collection.
The date of a guide is, wherever possible, taken from the guide itself, often from a copyright notice and just as frequently by studying the text. Sometimes, the date is deduced by its place in a series of guides for that wildlife park or zoo, whilst other times it is the date of a visit to a collection and sometimes it's just a wild guess.
It should be noted that the frequency that a zoo publishes and republishes a guide varies. There are periods when a new guide is published each year, sometimes followed by several years without a new publication. Occasionally, more than one guide per year will be published by the zoo.
Sometimes a zoo will change the cover of its guide, but not its contents; while sometimes they retain the cover of the guide, but some of its content will be updated. Copyright notices tend to give you the earliest possible date of a guide, as the same text can be used in subsequent guides with (say) a change to the cover.
The Zoo Guide Directory has tried to restrict its collection to guidebooks issued by the zoo or at the zoo.
Inclusion in The Zoo Guide Directory is given to zoos, wildlife parks, safari parks, bird parks and aquaria that are, or if closed they were, in the United Kingdom, Isle of Man and the Channel Islands.
A comprehensive list of UK zoo guide books is maintained by The Bartlett Society.