Contents of Nicholson's large files of bird lists and notes which he had organised on a geographical basis and inscribed accordingly. This arrangement is reproduced in the descriptions that follow. Some files were titled 'Bird Lists', others 'Bird Notes', but in respect of the material they contained, this distinction appears to have no signifcance. The files all contained envelopes relating to more specific geographical areas. These envelopes have been listed in the order in which they were found in the files. No chronological ordering of the papers was found in any of the enevelopes and no re-arrangement has been attempted.

Correspondence, very small pocket notebooks, and draft material for publications are occasionally found.

The organisation is as follows: England and Wales; Europe, excluding UK; and Non-European countries.