4.1   Extent

• Number of discrete colonies
• Population overall, numbers
• Distribution of population

4.2   Quality

• Distance between colonies
• Density of ants nests in sites

4.3   Objective statement

Maintain and expand the population of Silver-Studded Blue Butterfly in a favourable condition, WHERE:

4.4   Extent

Number of discrete colonies remain at current levels, or increases.

• Currently there are ten discrete colonies
• Target level: None set.
• Upper limit: None set
• Lower Limit: 10

Population, overall number of adults remains at current levels or increases

• 250,000 adults occur at the peak of the flight period
• Target level: None set.
• Upper limit: None set
• Lower Limit: current levels

Distribution of population remains at current levels or increases

• The ten populations occupy patches between 0.1 and 8 ha;

  • just one site is larger than 8 ha.

• Target level: None set.

• Upper limit: None set

• Lower Limit: current levels

Monitor/survey:

• larval web transects
• Standardised recording walk or 'transect' at flight times.
• Calcicolous populations usually emerge in June. Heath populations mid-July to August. The flight period lasts 4-5 weeks.

AND WHERE,

4.5   Quality

Distance between colonies patches is sufficiently close. Most adults do not disperse to lay eggs further than 50 m.

• Target level: None set.
• Upper limit: None set
• Lower Limit: 60 m for half the colonies
• Density of ants nests in sites > 30.ha

Silver-Blue butterflies do not occur where ant nest density falls below 30 nests/ha.

• Target level: None set.
• Upper limit: None set
• Lower Limit: 30 nests/ha
• Monitor/survey:
• distance between colonies
• Density of ant nests on sites colony sites

5.1   Ants

Females respond to the presence of ants when selecting sites to lay eggs. Mixed grazing regimes and old grasslands favour ants.

Monitoring and Projects:

• Monitor areas and density of ant nests.
• Monitor effects of mixed grazing trails upon populations of ants.

5.2   Bracken

Bracken can have extra-floral nectaries attended by ants. Sometimes the Silver-blue butterfly eggs are laid high on grasses or in clusters under the fronds of sparse Bracken Pteridium aquilinum at heights in excess of 30 cm.

Possible Conflict:

• With timing of bracken control measures.

Monitoring and Projects:

• Determine butterfly's dependency upon bracken
• Set aside area of bracken to be cut (ie. cut in bi- annual rotation)

5.3   Heathland

Ants are largely absent (<10 nests/ha) from dense or mature stands of heather. The exact conditions required by ant and butterfly are satisfied by heath vegetation in early successional stages of regrowth (2-5 years), usually <7 cm above the ground. The preferred conditions produce warm microclimates at ground level for the larvae.

A mosaic of heathland of different stages and a continual presence of early successional vegetation will be produced. Rabbit grazing and digging will prolong conditions on heathland (Thomas 1985).

Monitoring and Projects:

• Manage rabbit population, and provide feeding cover.
• Maintain continual presence of early successional stages of heath.

5.4   Calcicolous grassland

Females lay eggs on low vegetation <3 cm above the ground on calcicolous grassland in N. Wales. Moderate grazing by sheep will maintain suitable conditions on calcicolous habitats indefinitely.

Operational Limits:

• Target 1: Maintain sufficient patches of grass height within 3 cm limit.

Monitoring and Projects:

• Monitor grazing levels.
• Survey grassland sward height, to identify area of sward < 3 cm at least monthly.
• Target grazing to maintain sufficient areas of low sward.

5.5   Disturbed ground

Where topsoil is disturbed by grazers, or where burning of heath occurs, or firebreak is prepared, suitable conditions are produced.

Monitoring and Projects:

• Monitor bare ground on heathland (refer to Feature: Heathland).
• Monitor bare ground on grasslands

5.6   Dispersal and Isolation of habitat

Habitat patches shift. New patches of suitable habitat can be colonised by local dispersal of adult butterflies, but most individuals move less than 50 m over their life-span. Within heathland colonies, extinctions are confined to colonies of <0.9 ha. On limestone habitats, extinctions and re-colonisations most often occur on smaller patches <0.2 ha, where suitable conditions persist for shorter periods..

Monitoring and Projects:

• Monitor isolation of suitable and known sites, on heath and grassland.
• Monitor creation of suitable habitat, according to grazing variations.

5.7   Trampling

Sites and potential sites will not be permitted disturbance from trampling by visitors. Path detours will be resisted.

Grazing larger stock requires lower numbers to maintain sward conditions with less trampling, and to produce ideal structural conditions, with poached soil. Stock grazing will be carried out at time when trampling has minimal effects.

Monitoring and Projects:

• Safeguard areas from visitor disturbance.
• Determine optimum season for pony/cattle grazing according to butterflies' ecology.
• Introduce seasonal grazing with cattle and ponies on heathland.

Note: Implementation of this action plan could benefit other species of lowland heathland and grasslands, including the silky wave moth Idaea dilutaria.