|[Note Guidelines] Photographer's Note|
|Throughout most of it's range the Swallowtail shows itself to be highly adaptable, utilising a wide variety of habitats including sub-arctic tundra in Canada, prairies, woodlands and arid canyons in the south of the USA; hay meadows, roadside verges, river banks and sub-alpine pastures in Europe; high montane habitats in the Atlas mountains of north Africa, and semi-cultivated habitats in the Mediterranean area.|
It's adaptability extends also to it's choice of foodplants - in North America the caterpillars usually feed on Compositae ( Artimesia, Petasites ), while in Europe Rutaceae ( Ruta, Haplophyllum ) and Umbelliferae ( Foeniculum, Peucidanum etc ) are used instead. In Britain however the butterfly is restricted to a single foodplant - milk parsley, and breeds only at a very small number of wet fenland habitats in north-east Norfolk. Individual specimens have been tagged and found to fly over quite a large area, often reaching adjacent fens, but the butterflies do not stray beyond the general area of the broads.
Several centuries ago the species almost certainly occurred as a resident species over a much wider area of southern and eastern England, but later contracted it's range to the Great Fen - a vast area of wetlands covering Cambridgeshire, Lincolnshire and Norfolk. Following the drainage of this area, and it's conversion to agriculture, the butterfly was forced to contract it's range even further - to the Norfolk Broads. In such isolation the genetic diversity would have diminished, causing the so-called "sub-species" machaon brittanicus to become far less adaptable, and to acquire minor differences in appearance from the ancestral stock.
In the last 100 years the average wingspan of Swallowtails, and the average width of the thorax, have reduced in size, an indicator of further genetic impoverishment, which is likely to result in further contraction and eventual extinction. Expansion of the gene pool can only be accomplished by the introduction of genetically richer livestock from Europe, a policy which hopefully will eventually be adopted by conservation groups.
Although the butterfly only breeds in the wet fenlands and broads of Norfolk, migrants from France are periodically observed at coastal sites in Dorset, Hampshire, the Isle of Wight, Sussex and Kent. On 1st Sept 2003 for example I watched an immigrant Swallowtail flying across a main road at Milford-on-Sea in Hampshire. In most years less than half a dozen are recorded, usually in August or September. Individuals very occasionally penetrate further inland, and are reputed to sometimes breed on chalk grasslands, reportedly feeding as larvae on wild carrot Daucus carota, although I know of no recent records.
It is planned that by the end of the 21st century the Great Fens which formerly occupied much of eastern England will be partially restored, leading to a sizeable increase in suitable habitat. Whether such a project is feasible in the face of population expansion however remains to be seen.
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