This local survey is complete.
Rookeries have been surveyed in Hertfordshire for many years. In 2021 the Bird Club received records of 5,531 nests from 277 rookeries. See how this compares to previous Herts Rookery surveys below.
A new interactive map was produced to show the sites and nest counts, as well as known sites not checked, and sites previously used but found to be abandoned.
| Year of Survey | Total Number of nest counted | Total Number of rookeries counted | Mean Rookery size (number of nests) |
| 1960-61 | 15,739 | 521 | 30 |
| 1971 | 10,708 | 402 | 27 |
| 1975 | 8,685 | 375 | 23 |
| 1993 | 5,435 | 220 | 25 |
| 2015 | 3,343* | 192 | 17 |
| 2021 | 5,531 | 277 | 20 |
*survey coverage not complete
A full write-up of the survey can be found in the Hertfordshire Bird Report 2021