A walk around the Heath may reveal over thirty different birds. Meadow Pipits, Skylarks and Grey Partridges nest in the open grassland, which also provides a hunting ground for Kestrels and other birds of prey. The scrub margin is ideal for Yellowhammers, Whitethroats and Thrushes. In winter hundreds of Redwings and Fieldfares feed on the Hawthorn berries. In the woodland you may see or hear Spotted Flycatchers, Tawny Owls or Woodpeckers.
Since man first came to settle in this area sheep have grazed on these slopes. Constant grazing has determined the vegetation of the open grassland, and has kept invasive species such as Hawthorn at bay. On parts of the Heath over thirty different species of plants may be found within a square metre, supporting a wide range of insects, birds and mammals.
Many plants thrive on this chalky soil, including some great rarities. To see a monthly list of species click here.
Of these the Pasque flower, Anemone pulsatilla is one of the most spectacular. Around Eastertime the best surviving concentration of this plant in Britain can be seen flowering on Church Hill. Other rare plants to look for include the Spotted Cats Ear, Bastard Toadflax, Wild Candytuft and Lesser Meadow Rue. Several species of Orchid grow on the Heath, and it also harbours many different mosses, lichen and fungi.
Keep an eye open for some of the animals which use the Heath, such as Stoat, Voles, Hare and Muntjac Deer. On a sunny bank you may see a Common Lizard; this is probably the Heath’s only reptile and is quite harmless. The Reserve also provides a refuge for a spectacular range of insects and spiders, including rare Picture-wing flies.
The Heath is designated a Local Nature Reserve and a Site of Special Scientific Interest. This is because it is one of the best remaining chalk grassland sites in the country, containing a great range of plants and animals, some of which are very rare. These species have disappeared on the surrounding land due to changes brought about by agriculture, urban development and road building. Over 80% of this sort of habitat has been lost since 1945.
On a summer’s day you may come across a dozen more species of butterfly. Some of these are quite scarce, as they require plants and conditions which only chalk grassland such as this can supply. One butterfly which is a speciality of Therfield Heath is the rare Chalkhill Blue, which emerges in late July and can only be seen for about six weeks. During this time the female lays eggs on or near the caterpillars’ food plant, Horseshoe Vetch, where they remain over winter. In later April the caterpillars emerge, feed, and from Mid-June onwards, chrysalises are formed. During its life-cycle the Chalkhill Blue maintains a curious relationship with ants. In return for protection, both caterpillars and chrysalises secrete honeydew as food for the ants. Each chrysalis even has a special sound organ which it uses to attract its guardians’ attention. When the fashion for butterfly collecting was at its height the Chalkhill Blue was almost hunted to extinction on this site. Now, thanks to careful conservation work, the future of this butterfly is more secure.
Can I pick the flowers?
Sorry, but no. It is an offence to remove or displace any soil or plant, or to disturb any animal on the Heath. So please leave the wildlife for others to enjoy.
The Conservators are grateful to Alan Beale of Royston who monitors butterfly numbers on the Heath. His notes may be seen here. More information about butterflys on the Heath can be found here at the Butterfly Monitoring Scheme