Hertfordshire & Middlesex Branch

Hertfordshire & Middlesex Transects

Over 75 transects were walked in Hertfordshire and Middlesex in 2023

Transects are the main method of measuring how butterfly populations change with time. The technique is simple, involving walking the same set route every week in good weather throughout the summer months, and noting down the numbers of each species seen within about 5 metres. The method is described under BUTTERFLY TRANSECT MONITORING

The transects walked in Hertfordshire and Middlesex since 1978 are listed here - some have been walked for over 25 years which enables us to understand the long-term population changes in butterflies. Please note that some transects have not been walked continuously.

If you would like to start walking a transect, do look at this list to see whether there is one near to where you live which is no longer regularly walked first.

Case Study
In 2018 the branch gave habitat advice to the site managers of Chorleywood Common. Several changes were made to the way the site was managed which included light grazing and creating clearings in the woodland areas. A transect was set up and this report clearly shows how important transect monitoring is, and how the improvements that were made increased the butterfly numbers. Chorleywood Common 2018 - 2023

Link sections on this page . . . Transect recording information and instructions