Long-term butterfly monitoring scheme in Britain.

The Scheme was set up in 1976, after 3 years of preliminary trials, and is
a joint project between ITE and the Joint Nature Conservation Committee.

The scheme was set up with 2 aims:

1) to provide information on the fluctuations of butterfly numbers from
year to year, so that underlying trends can be assessed.
2) to detect changes from the overall trend at individual sites, that are
caused by local factors, such as management.

In addition to the initial aims, the scheme also provides information on
aspects of the population ecology and phenology of butterfly species, both in
relation to the effects of changes in climate and as a contribution to basic
knowledge.

It is the only long-term monitoring scheme of its kind in Britain.

The methods used are described by Pollard (1977) and instructions for
recorders are available as a separate booklet.

Briefly, at each site the recorder makes a series of counts, walking a
fixed route once a week from April to September, noting any butterflies seen
within 5 metres.

To provide standardisation, walks are carried out only between 10.45 and
15.45 BST, and then only if the weather meets specified criteria.

Transect routes are divided into sections, usually according to changes in
habitat, so the scheme provides information on habitat preferences of
different species, and gives a means of objectively assessing the effects
of management on species.

Over 100 sites from the whole of Britain and Northern Ireland now
contribute to the Scheme each year. Results are analysed in several
different ways.

At each site, the mean weekly count of each species is totalled to
provide an annual index of abundance. The index of abundance is not a
population estimate, but has been shown to be related to propulation size
(Pollard, 1977).

The annual indexes of abundance from all sites are then collated to
give either an "all sites" or regional index (Moss and Pollard, 1993).

The fluctuations of the regional or "all sites" trends, can be used
as a baseline for comparison with specific sites to assess the effects of
local management (Pollard and Yates, 1993).