Adur Valley Wildlife
MILL HILL Local Nature Reserve
Old Shoreham, West Sussex
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Plan of Mill Hill and the adjacent areas

Mill Hill and the surrounding DownsSouthern end of Mill Hill Nature ReserveMill Hill CopseSpecial area for butterflies and wild flowers near the reservoirShoreham BankWoodland since 1971Old Erringham FarmMixed long and short sward Hawthorn scrub with ThistlesField grazed by sheep and cattle, with buttercups (Pasture)Field of ThistlesCattle grazed field with RagwortSheep grazed pastureMeadow with sheep grazing at timesIntermittent horse grazing and neglected land
Horseshoe Vetch on Mill Hill (Photograph by Ray Hamblett)

Lower Slopes of the Downs near Mill Hill
The yellow is Horseshoe Vetch

Scrub, in transition to secondary woodland, with Dogwood, Hawthorn, with cleared glades.
Area of scrub, copse with glades and clearings: 9.4 acres
Copse planted with Corsican Pines, Norway Maple, Italian Alder and Beech, replacing an older planted copse of more unusual trees planted in honour of Canadian war dead. 
Mixed grassland with long swards, and short sward in the more exposed places. Forage harvested in late autumn.
8.6 acres
Famous "Chalkhill Blue" lower steep slopes covered with authentic original short sward chalkhill herbland, dominated by Horseshoe Vetch, and providing habitat for thousands of butterflies
6.4 acres
Elderberry and Hawthorn scrub with a variety of grasses and wild flowers. Not forage harvested. 
Overgrown and overnutrified approaches on the Mill Hill Nature Reserve, reminiscent of neglected pasture land. Forage harvested in late autumn. Dug up for the Waterworks in the past. 
2.7 acres
In 1960, this woodland of Sycamore, Ash and Hawthorn, with Holly, Elderberry etc. was open bare downland in 1960. 
6.2 acres
Arable land
Traditional grazing land. 
Land grazed heavily by cattle and sheep, eroded.
A: Meadow: harvested for hay
B: Pasture: rotational grazing only
Land grazed by horses with a small patch of neglected land. Wild Roe Deer.
Former arable land that is grazed by cattle.
Former arable land that is grazed by horses with Bird's Foot Trefoil.
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and key to the symbols
6 = Mill Hill


Mill Hill
Southern Car Park


Shoreham Bank (Mill Hill)
Shoreham Bank (Mill Hill) is the most nationally famous of the Sussex butterfly sites.

Photograph by Andy Horton
Chalkhill Blue (Photograph by Andy Horton)
Adonis Blue
Chalkhill Blue

This fame was created by the huge numbers and aberrations of the Chalkhill Blue Butterflies. The fame started from about 1820 when butterfly collecting became the vogue. During the heyday of butterfly collecting between the two World Wars, the site was kept a secret by commercial collectors. In 1938 the area of Mill Hill and other downland was presented to the people of Shoreham, some 724 acres, although less than 28* acres remain as public open land. It was rediscovered in 1955. (*may be 30 acres)

Despite the large number of collectors, they did not cause the decline of butterflies on Mill Hill but the demise of the rabbit through myxomatosis and the invasion of scrub through the absence of the rabbit. This disease arrived in 1954, but in the cold winter of 1963, the hill was still almost devoid of scrub. The main invasion of woodland and scrub occurred from the mid-1960s. 

In the 1950s (before my time) the area was fenced off and the upper slopes were grazed with cattle. The area was grazed right down and only Ragwort remained (like the fields adjoining nowadays). This seemed to have encouraged Hawthorn scrub, Dogwood and Creeping Thistles which remain today. The reports from butterfly collectors said that all the Horseshoe Vetch and wild flowers had been lost from the upper slopes. This remains the case in 2003, although there are now large swathes of longer grass and Scabious, Greater Knapweed, etc. The lower steeper slopes were fenced off and this is still a continuous mat of Horseshoe Vetch with incursions of Wild Privet. Chalkhill Blue Butterfly femaleThere is a report of a recovery after the cattle were removed and by 1960 there is an authentic report of 6000 Chalkhill Blue Butterflies seen on one day. In 1967 grazing was banned and this resulted by 1971 in a sudden growth of the long grasses, which are now forage harvested in late autumn. Volunteers than helped with scrub clearance but no lasting impression was made on the problem. In the late seventies, I still observed hundreds of Chalkhill Blue butterflies that had descended to the Waterworks Road where the grass was mown, but this area has been neglected and is now covered in nettles. 

In 1990, cattle were again introduced to the upper slopes for a short period. The area looks very much like a lowland cattle pasture ten years later. Although the upper slopes now support large populations of many hundreds of Common Blues and Marbled Whites in the longer grasses, this seems to be at the expense of Chalkhill Blues. Erosion has been caused by hang-gliders and other human activities, but it appears that is not as great as the damage caused by cattle.

In 2003, my summer survey revealed that Horseshoe Vetch was still abundant on the lower slopes covering only about five acres, but that the same species on the middle and upper slopes is very small in area and does not support Chalkhill Blue Butterflies. Scrub incursions are very serious and a woodland has developed where there used to be bare hill. However, in the main breeding area on the lower slopes is still maintained although the scrub is making serious incursions, led by Wild Privet. The numbers of Chalkhill Blues seen on one day was 3000*, which roughly corresponded to previous years, but this represents about one half of the number for 1960. The only major management change in this time has been cattle grazing. 

Altogether at least 30 species of butterflies have been positively been identified by myself in the last three years, and I expect this total to increase. In season the Chalkhill Blue still remains the most prevalent butterfly, with small population of Adonis Blues and Dingy Skippers, mostly on the lower short ward (20 mm to 35 mm) herbland. Large numbers of Common Blues and Marbled Whites are to be found on the upper slopes and these will most likely to be seen by casual visitors, although the dispersals of Chalkhill Blues will venture over the whole area in the search for nectar plants.

Mill Hill is now managed by the South Downs Conservation Board, who have taken over from the West Sussex County Council. 

Chalkhill and Common Blue Butterflies (Photograph by Andy Horton)Major reference:

A Revised History of the Butterflies and Moths of Sussex 

Colin R Pratt
Booth Museum of Natural History 
CD-ROM  1999 

Link: Chronological History

The meadow to the west of Mill Hill is now 15 acres.
Local Nature Reserve Designation

A Nature Reserve is defined in Section 15 of the National Parks and Access to the Countryside Act 1949, as land managed for the purpose:
(a) of providing, under suitable conditions and control, special opportunities for the study of, and research into, matters relating to the flora and fauna of Great Britain and the physical conditions in which they live, and for the study of geological and physiographical features of special interest in the area; or
(b) of preserving flora, fauna, or geological or physiographical features of special interest in the area; or for both these purposes.
Article in the Shoreham Society Newsletter

Past & Present
Link to the Adur Nature Notes 2008 web pages
Link to the Adur Butterflies web page
Adur Nature Notes 2016
Hippocrepis comosa (Horseshoe Vetch)
Magic Map of Mill Hill NR
View over the River Adur (by Ray Hamblett)Beech (Fagus sylvatica)Italian Alder (Alnus cordata)Norway Maple (Acer platanoides)