The Observer's Book of British Birds (1937)

The first Observer's Book was The Observer's Book of British Birds by S. Vere Benson, published by Frederick Warne in 1937. It became The Observer's Book of Birds in later editions, so a copy titled simply Birds is not the 1937 first.

What to check:

• Title: The Observer's Book of British Birds.
• Binding: brown cloth lettered in black on the spine and front board.
• Jacket: early jackets are plain, with a pattern of squiggly lines at the top. A first edition should be in a jacket from 1937, not a later one.

Warne kept the book in print for decades, revising the text several times, and dealers sometimes sell later impressions of the 1937 text as first editions. Warne printed a code in its books that records when each printing was made, so a later code means a later printing even if the title page looks the same.

Jackets are the most important part of the value. The series went through many jacket variants, and later jackets carry higher prices, so the price on the flap is a quick check. A copy without its jacket is worth very little.

The early books did not carry their series number. No. 1 is the number collectors and Warne's later lists give it.

Sources: Wikipedia, collectingbooksandmagazines.com and dealer listings.