Home The Butterflies of Gloucestershire Species Habitats Conservation

Conservation

The main conservation issues affecting butterflies include:

Other relevant issues are:

Other wildlife interest

The habitat for uncommon or scarce butterfly species supports a very wide variety of other forms of wildlife. Some is still reasonably common and widespread in the countryside, some is confined to a particular type of habitat.

Some rarities are found in just one or a few sites in the area. Examples include numerous plants (e.g. some orchids), and many species of invertebrate (other types of insect, spiders, snails etc).

Good butterfly habitat supports our local biodiversity, and conservation measures need to take other wildlife interest into account.

Habitat destruction

 Much of the unimproved grassland which remains in the Cotswolds is on steep slopes. Most of the more level areas have already been ploughed up or treated with fertilisers and pesticides, with the result that most of their natural history interest has been lost. Even the steeper sites are at risk of destruction: small remaining areas of steep unimproved grassland are sometimes planted with trees. Species which have lost colonies for this reason include Duke of Burgundy and Chalk-hill Blue

Other changes in land use can also destroy butterfly habitat, but indirect destruction through lack of management is probably a greater threat.

Lack of management - grassland
Conversion of surrounding fields from pasture to arable crops has removed the grazing from some of the remaining grassland sites. Formerly short turf supporting several scarce butterfly species is soon replaced by long turf supporting less diversity. Hawthorn or gorse scrub gradually spreads over the site, and eventually the open grassland is completely lost.

The spread of scrub is illustrated by these two photographs, where both sides of a small valley used to be grazed in the 1970s and the grassland was rich in flowers and butterflies. At some point the grazing of one side was stopped or very much reduced, and the later photograph shows the increased extent of scrub cover as a result. The upper photograph was taken in 1976, the lower one in 1994.

This hawthorn thicket has covered an area of grassland which used to support a Duke of Burgundy colony. The colony had survived for many years in a small clearing with plenty of cowslips, but eventually it died out.

Lack of management - woodland

Most woodland butterflies need open areas along tracks, in clearings and in scrubby areas. In woodland which is actively managed as commercial forestry there are plenty of such open areas. In woodland which is allowed to mature to dense stands of tall trees with no regular felling, open areas soon become shaded out and the wood becomes unsuitable for some butterfly species.

The Pearl-bordered Fritillary used to occur in many Cotswold woodlands. It has now gone from most of them, and whether or not lack of management was the original reason for this, many former sites are no longer suitable for the species.

Too much grazing

 Moderate levels of grazing, usually by sheep or cattle, can maintain unimproved grassland in ideal conditions for butterflies, flowers and other forms of wildlife. Long periods of heavy grazing make a site much less suitable for butterflies, by removing either the larval habitat or the nectar sources for adults. Adult butterflies also need some tall grass or other vegetation on which to rest overnight.

One strong Small Blue colony was centred on part of a grassland field, and its eggs could be found on several much smaller patches of kidney vetch in the surrounding area, including two roadside embankments. Most of the field was ploughed up and although the main area of kidney vetch remained, it was then grazed much more heavily than in the past. The main Small Blue colony seems to have died out, and it has also not been recorded on most of the smaller sites since then.

One large area of unimproved grassland is managed mainly for its botanical interest, and grazed heavily. It does have quite a good range of grassland butterfly species, but populations are much lower than on smaller lightly-grazed sites. It too has lost its former colony of Small Blue.

Heavy grazing in woodland can have a similar effect, and parts of the Forest of Dean are not as good for butterflies as one might expect.

Colony isolation

 For some scarce species, loss of habitat has left many of their colonies isolated on small areas of good habitat in an otherwise unsuitable landscape. Such colonies are very vulnerable to local extinction from a range of causes, and their isolation makes natural recolonisation very unlikely. Several colonies of Duke of Burgundy and Grizzled Skipper seem to have been lost in this way, even though the sites now appear to remain suitable.

Disease and parasites

 Habitat changes or weather conditions often appear to be the cause of population declines, but sometimes there is no obvious cause and disease or parasitism seem more likely.

It is known that as the Holly Blue population builds up to a peak over several years, so too does the population of a parasite which eventually causes a crash in the populations of both. The cycle then repeats.

Environmental changes

 Global warming is thought to be the reason why the distribution of some species is expanding in Britain. In our area the Essex Skipper is spreading across the Cotswolds and into the Severn Vale.

Particularly wet or cold summers can reduce breeding success, leading to population declines and local extinctions.

Particularly dry summers can also be very damaging, with larval foodplants withering and nectar sources drying up quickly. What was perhaps the best Duke of Burgundy colony in the area became just another small colony after a drought, although the introduction of grazing to the site probably also made its cowslip foodplants more vulnerable to drying out during the summer.