What are Transects?

There are several ways of counting butterflies:

Specific habitat surveys:- for example, visiting all the local chalk downlands.
Saturation surveys:- like our Stubhampton Bottom count when we comb the area for most of the Pearl-Bordered Fritillaries we can find.
Spot sightings:- noting what you see and where (if you do this, please send your records to Dorset Environmental Records Centre (DERC).
Transect walking.

This is written to take the mystique out of Transect walking.

All that is meant by a Transect walk is a regular weekly count of butterflies along a particular route. There are some rules, but anybody can take part, whether they are beginners or experts; indeed, it is an excellent way for the beginner to learn butterfly identification.

Some years ago when many areas of Dorset began to become Nature Reserves those of us interested in butterflies wanted to make sure that they were being looked after properly. Many reserves had no full time wardens to look after them and this made action of some kind even more important: reserves have to be managed or they simply become overgrown and lose the species which they were designed to protect. But how could busy, amateur committees ensure that the Reserves' programmes of scrub clearance, grazing and cutting were not harming the butterflies?

In the 1970's Dr Pollard and other researchers at the Institute of Terrestial Ecology (ITE) at Monk's Wood devised a method for recording the fluctuations in the abundance of butterflies. A Reserve was divided into Sections (also called Sectors or Transects). For example, Section 1 might be through woodland, Section 2 through scrub and Section 3 through open grassland. A walk was then planned to pass through all the Transects, and the same route was followed by the butterfly walker at least once a week. As the walker proceeded, a count of the numbers of butterflies from each species was kept and totalled up for each separate Section of the walk. It was important that certain walking rules were constantly obeyed from week to week and from year to year to ensure consistency.

The whole point of the walk is not to produce an accurate count of all the butterflies on the reserve but to measure any fluctuations from week to week and from year to year. Failure to keep to the rules, listed in this booklet, would mean that any comparisons made between, say, the numbers seen in one year and another would not be valid. It can easily be seen that this idea of the Transect walk was just what was needed to monitor the changes on nature reserves. If the management decided to cut the scrub or change the grazing density then the records from the appropriate part of the walk would show whether this had a harmful or beneficial effect on butterfly numbers. The ITE at Furzebrook in Dorset set up a walk at Ballard Down near Swanage in 1976, which is still being operated today.

When the Conservation Officer for the Dorset Wildlife Trust suggested that it would be useful to monitor the butterflies on Fontmell Down, the idea of a team Transect walk was devised. In March 1980 four amateur entomologists met to plan out which weeks they could walk and devise a route at Fontmell Down which would cover the main types of habitat and the known areas used by the different species of butterflies. From this "Dad's Army" approach to the monitoring of butterflies sprang the present network of walks which now totals forty-four.

From the table of walks it can be seen that there are many types of walk: some are long and have many different sectors or Transects, whilst others are short and have only one sector. There are walks in woods, heathland, downland and coastland. The walkers (over 100 of them now), are as varied as the walks and habitats. Since 1980 Fontmell Down has been walked by schoolteachers, nuns, nurses, dentists, engineers, clergymen, housewives, retired ladies and gentlemen, the self-employed and unemployed. The last three categories are in much demand with walk organisers as they can walk in mid-week when everyone knows the weather is much finer! During the winter or early spring the volunteers meet to decide the walks and in which weeks they will be able to operate. During the summer months they can be observed with clipboards or tape recorders following the routes marked out on their maps or sometimes on marker posts. In October, with the walking season over, the records are collated, put onto computer and the results interpreted, to be conveyed to the various reserve management committees, to DERC, and, at meetings, to the walkers.

One major problem remains to be solved. If, say, Common Blues on one reserve decline, how are the management committees to know whether this is due to the management of the reserve or because of external factors like the weather? Reserves which are monitored by professional wardens participate in a central scheme run by Monk's Wood. Reports are collated from all over the country and reserves can work out whether their butterflies have behaved in the same way as everybody else's or done something different. This central report has also been made available for the Dorset walkers to examine. As well as this, the Dorset Branch are planning to collate official weather records from all over Dorset which, when interpreted against the Transect walk data, will help us to eliminate fluctuations in butterflies caused by the weather conditions.

More walkers are always needed. It is hoped that if you do not already walk, this might inspire you to try it out and join one of your local walk teams! Do not be put off walking because you think you cannot identify butterflies: joining a walk makes this relatively simple. Make sure you have a good book on butterfly identification and that your walk leader gives you last year's results. Once you have decided which weeks you are going to do the walk, look up what was seen the previous year and study your book carefully before you go out. In addition to this, we run many field meetings which are designed to help: all are welcome and they are free - ask for our Events list.

If you are interested in becoming involved in Transect Walking, please contact Bill Shreeves.

Click here for a checklist for Transect Walkers.