The ecology and conservation of the heath fritillary butterfly, Mellicta athalia. III. Population dynamics and the effect of habitat management
Published source details
Warren M.S. (1987) The ecology and conservation of the heath fritillary butterfly, Mellicta athalia. III. Population dynamics and the effect of habitat management. Journal of Applied Ecology, 24, 499-513.
Published source details Warren M.S. (1987) The ecology and conservation of the heath fritillary butterfly, Mellicta athalia. III. Population dynamics and the effect of habitat management. Journal of Applied Ecology, 24, 499-513.
The heath fritillary butterfly Mellicta athalia is a rare and declining species in the UK. It is extremely sedentary butterfly with precise habitat requirements; its breeding habitats are often ephemeral and need regular management. This makes it a difficult species to maintain on nature reserves, particularly if they are small or isolated. Experience has shown however, that it is possible to maintain populations on reserves, provided they are large enough and correctly managed. This study was undertaken primarily to examine fritillary population fluctuations and the effect of incidental or deliberate habitat management, and from this, make recommendations about the practical conservation of M. athalia and identify the factors causing its decline in Britain.
Forty-three heath fritillary Mellicta athalia populations in woodland and grassland habitats was monitored in 1980-84 in Kent (where the species occurs in woodland) and in 1980-85 in S.W. England (where it is predominantly found in more open grass heaths).
Here the findings of the effect of management on Kentish populations are summarised.
Study sites: Monitoring of heath fritillaries was undertaken at the 26 Kent (south east England) colonies known in 1980.
Butterfly sampling: The relative size (the number of sightings per site or the number of sightings per hour x area during a single visit at the peak flight period) of all colonies was estimated during most years in 1980-84. Butterfly monitoring transects were also used to monitor adult numbers. This sampled butterflies throughout the season and produced an index of adult abundance, which can be used to monitor yearly fluctuations in population size. The index is therefore likely to be more accurate than relative estimates obtained from a single sample, and was used preferentially wherever possible.
Habitat management Habitat management interventions were recorded at each site in order to relate these to heath fritillary population fluctuations.
Colony size fluctuations: The size of all heath fritillary colonies varied greatly during 1980-84, with many becoming extinct while others flourished (15 of the 26 colonies known in 1980 had died out by 1984). Extinctions were partly offset by the establishment of 10 new colonies. Colony size fluctuations appeared largely independent of each other with no consistent pattern from year to year. In every year some colonies increased while others decreased and a few became extinct, regardless of habitat type e.g. vigorous coppice (i.e. well-stocked and fast growing), poor coppice (i.e. poorly stocked and/or slow growing) and coniferous plantations. Weather was not therefore considered important in determining these fluctuations.
The factor that appeared most important was length of time since the habitat was coppiced or cleared for conifer planting. Regardless of habitat type and area, trends after cutting followed the same pattern: populations peaked 2-4 years after cutting, and then numbers declined at a rate that varied according to the habitat. In vigorous coppice (rapid regrowth), numbers declined extremely rapidly after the fourth year and all the colonies had become extinct by the sixth year after cutting. Populations in poor coppice and conifer plantations (slower regrowth) declined far more slowly after their peaks and a few remained at low densities 10-11 years after cutting.
Colonization of newly cleared or coppiced areas: Colonization of newly cleared or coppiced habitats occurred mostly in the first summer after cutting, but at two sites 2 and 3 years after where butterfly numbers built up very rapidly.
Habitat creation: A number of additional potentially suitable habitats were created within the Blean Woods complex during the study period but were never colonized. These were within 600-1,000 m of the nearest known colony and interconnecting rides were sometimes present. Within the Blean Woods National Nature Reserve, however a programme of conservation management was introduced in 1979, specifically for heath fritillaries. New areas of 1-3 ha were cut every year subsequently. In 1980, the peak population was estimated at < 20 adults but, after a few years, this rose rapidly to around 600 adults in 1984, attributable to the increased management, with an estimated 1,100 adults at peak in 1985, representing a total emergence in the region of 3,000 adults.
Conclusions: In its woodland habitats in Kent, heath fritillary population size varied according to the time of coppicing or clearance. Populations usually peaked 2-3 years after cutting and then declined rapidly. All colonies in vigorous coppice regrowth became extinct by the fifth year after cutting and in conifer plantations by the ninth year. This was related to the rate of regrowth in each habitat.
The decline of the heath fritillary in Kent (and elsewhere in Britain) is attributed to the decline of coppicing as the major form of woodland management, as well as extensive habitat loss.
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