Butterflies are mobile and often highly visible species. Some species exhibit a metapopulation structure, with colonies in discrete areas of suitable habitat. Colonies may become extinct, and the areas are then recolonised. Failing to find a species on a site in one or more years can therefore not be taken as proof of absence; negative results from several years would be needed to confirm this.

Presence–absence of adults is the simplest method for monitoring butterfly populations and will usually be used to establish baseline data at sites that have not previously been surveyed. More detailed survey and monitoring of larval or egg numbers can be made by using timed counts or quadrats and transects once presence has been established. For species of conservation importance, some sites will have already been identified and monitoring schemes will normally already be in place. However, surveys of other sites are obviously required, since it is unlikely that all breeding areas have been identified, and you will need to look for range expansions out of known sites.

ATTRIBUTES FOR ASSESSING CONDITION

Population range

Area of occupancy is an important attribute to survey and monitor and can be best assessed by mapping presence–absence in areas of suitable habitat. Repeat surveys will illustrate expansions or contractions of range. Monitoring habitat extent with occasional confirmation of presence may be the most practical approach in some cases.

Colony numbers

Butterflies often live in breeding areas defined by areas of suitable habitat.