Worcestershire Record No. 19 November 2005 pp. 47-54

WORCESTERSHIRE BUTTERFLY TRANSECTS 2004

John Tilt

This is a brief outline of the transect results up to 2004 for this area. Transects are our main vehicle for monitoring butterfly populations.

Analysis and interpretation of the results of such a survey should always be done with care. As we all know counts can be influenced by numerous factors. The main variables are weather, habitat change and the number of visits to the site. None of these factors remains constant so even in transects which have been repeated over a considerable time population trends should be treated with caution. E.g. The reduction of a particular species on a transect may mean that the habitat is no longer suitable or that the transect walker has been unable to record in ideal weather that year

The survey requires the transect to be recorded for 26 weeks. The ability of the Transect Walker Software to adjust values when weeks are missed is less than perfect. New software is due, which will solve these problems. As an interim measure I have used Total Count and also peak count for each species and each site which still uses data when a full number of observations have not been made.

Thanks to the many Transect Walkers who contribute to these data.

The tables below give an overview of the records in 2004 and the last 10 years. 2001 (Foot and Mouth year) is excluded.

The report makes no attempt to draw any conclusions from the data. All results are sent to BC Head Office to be analysed against habitat change and weather conditions.

Page 9 shows how, on an individual basis, conclusions can be drawn. Honeybourne is losing Grizzled Skipper due to lack of habitat management. The effect of opening up rides is shown in the increases in Meadow Browns at Grafton etc.