This volume was produced as a supplement which concentrated entirely on natural history. The whole of Volume 20 has been digitised as a single pdf; the file size is 4.1 MB. Volume 20 was issued as a ‘Special Supplement’ which concentrated on ‘Natural History, 1957’; it was published in 1959.
The contents are listed below:
| Title | Page No. |
| Birds in Hampshire, 1957: Forward | 1 |
| List of Observers | 2 |
| Bird Records, 1957 | 4 |
| Addenda to 1956 Report | 56 |
| Corrections to 1956 Report | 56 |
| Report on New Forest Dipthera | 56 |