The British subspecies of the large copper Lycaena dispar dispar formerly occurred in a few localities in the East Anglian fens; the last individual was reported in 1851. The Dutch race (L.d.batava; closest in appearance and ecology to L.d.dispar) was introduced to Woodwalton Fen (Cambridgeshire, eastern England) in 1927 and survived until 1969; an exceptional flood in 1968 submerged the larval food plants (great water dock Rumex hydrolapathum). Only one male and four females emerged in 1969, but no pairing occurred. Here the re-introduction of the butterfly in 1970 from captive stock, population growth in the following three years and results of a cattle-grazing experiment, are summarised.
Captive-bred releases: In late summer 1970, larvae and pupae (from two captive populations of Woodwalton stock) were placed in muslin cages distributed in eight (approx. 2 to 4 ha) compartments on the Fen, from these 517 male and 551 female butterflies were released. Further releases were made: 1971 – 208 males, 344 females; 1972 – 294 males, 430 females; 1973 – 446 males, 554 females. Egg counts, larval emergence and estimates of eggs laid per female, were made each year.
Cattle-grazing: Grazing has previously been shown to make areas more attractive to ovipositing females by exposing dock plants through reducing density and height of other vegetation. In the summers of 1972 and 1973, compartment 53 (4.16 ha) was grazed by six bullocks (i.e. at low intensity) from 31 May to 2 August 1972. The similar, adjacent compartment 57 (3.33 ha) was not grazed (as a control). Compartment 52 (2.33 ha) was also monitored, being comparatively open due to more recent and numerous experimental peat excavations than in 53 and 57. Egg counts were made on all dock plants in the first week of August 1972 and 1973.
Numbers of emerging larvae, eggs counted and eggs per female increased each year:
1970 – larvae 0, eggs 2,672, eggs/female 4.9;
1971 – larvae 111, eggs 6,509, eggs/female 31.1;
1972 – larvae 427, eggs 21,089, eggs/female 71.7;
1973 – larvae 1,344, eggs approx. 40-45,000, 2,672, eggs/female 89-100.
Effect of cattle-grazing on vegetation: Grazing and associated trampling created a mosaic of short and taller vegetation (average height 0.6-1 m, with patches of Phragmites communis reed and other plants up to 2 m) and exposed a large number of dock plants. The catte did not graze great water dock but a few were damaged by trampling. Trampling exposed some patches of bare peat, serving as a potential germination bed for water dock seed.
In compartment 57, most vegetation at the beginning of August was between 1.7-2 m in height. In compartment 52 the average height was 1.2 m except along some margins where the reed reached 2 m.
Egg counts: In 1971 (before grazing was initiated) compartment 53 had 0.11 eggs/plant. In 1972, it had 3.1 eggs/plant, higher than in compartments 52 (1.7) and 57 (0.1). In 1973 the trend was similar: compartment 53 (2.1 eggs), 52 (0.4) and 57 (0.3).
No further systematic egg counts were made in these compartments but in summer 1976 the warden reported compartment 53 (where grazing was continued) as still one of the best copper breeding sites. Although the results suggest that egg production improves when the vegetation is lightly cattle-grazed, the author highlights that this is not proof of success as it was not possible to replicate the treatments.
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