Transect Monitoring - Herts & Middx Butterfly Conservation

Transect Monitoring

Transect recording in Hertfordshire & Middlesex

Over 75 transects were walked in 2023 in Hertfordshire and Middlesex.

The transects walked in Hertfordshire and Middlesex since 1978 are listed here - click on link for more details

This is the most formal method of recording and should only be carried out by experienced observers who can recognise virtually all butterfly species on the wing and who can commit to walking a set route for all or most weeks from the start of April to the end of September.

A route should take about 30 minutes to walk when there are no butterflies, as this will expand to more than an hour at the height of summer. A good length is between 1-3 kilometres (up to about 2 miles). The route is divided into sections that correspond to particular habitats and there can be up to 15 sections.

This method gives information on the variation in butterfly numbers within the season, and from year to year and can also be invaluable in helping to guide and review management for butterflies on a particular site..

The route must be walked in set weather conditions:

  • Temperature of 13C or greater with at least 60% sunshine over the route. If the temperature is 17C or greater the the amount of sunshine does not matter
  • Wind speed no greater than 5 on the Beaufort scale (i.e no more than a strong breeze)
  • Note the numbers of each species of butterfly seen within a set distance from the observer, usually 5 metres.
  • Between 1045 and 1545, once a week with weeks beginning on April 1 and ending on September 29, so in 2024 for instance each week begins on a Monday.

There are some weeks, particularly early in the season, when these meteorological conditions cannot be met. Again it is better to walk the transect when it is a bit too cold or too cloudy rather than not to walk it at all, but a careful note of conditions should always be kept.

Records are ideally submitted each week onto the Transect Walker online at the UKBMS website. Registration is needed to use this site and to register a transect if it is a new one.

Andrew Wood (details on Committee page) the local UKBMS coordinator has access to all the records entered and checks the data input and will query any unusual records.