I found this review of that well known publication, still used as a point of reference today, The Birds of the North Kent Marshes, in the RSPB magazine for Autumn 1950.
The North Kent Marshes are a very special area and worth preserving at all cost.
I've really enjoyed the Northward Hill section in Birdwatchers' Year (published by Poyser Monographs). Jim Flegg, who was involved in regular visits to the reserve and bird ringing, gives interesting month by month accounts of birds seen on the reserve with other natural history details. Unfortunately, it was published in 1973, although it is still fascinating. I often wonder whether his experiences are still representative of what can be seen today.