Friday 10 January BBC2 8.00pm
Bill explores the legendary land of Avalon - a strange otherworldly landscape that should by rights be under water. The Somerset Levels and Moors are the largest area of lowland wet grassland and grazing marsh remaining in England. It is some of the lowest, flattest land in the country that was once a great marshy sea. They are of outstanding nature conservation importance for the rich, varied mosaic of wet grasslands, reed-beds, mires and fen meadows, with 8000 km of rivers and ditches. Despite being several kilometres inland, they are below sea-level, and every winter huge areas flood. Birds, plants, insects and mammals are here in abundance and include wintering wildfowl and waders; birds of reed-bed and flood meadow; plants and insects of ditch and ancient pasture.

When to visit and what to see
Bill visited in early May, just as Spring was getting into gear. Resident herons and grebes are well into breeding but most spring migrants have only just arrived and are singing their hearts out. The dawn chorus is spectacular, a wall of warbler song featuring sedge, reed, Cetti's, grasshopper and willow warblers, chiffchaff and blackcap, plus cuckoos, robins, wrens, blackbirds and song thrushes. During the last week of April, first week in May, up to 1000 Whimbrel pause here on the peat moors for a fortnight or so, before heading north to breed. With about 200 Curlew also present it is a great chance to compare the two species.

Many of the moors remain wet through Spring into early Summer, perfect conditions for breeding waders. Redshanks, snipe, lapwing, curlew and black-tailed godwit all nest on the wet meadows, while willow beds support breeding populations of reed bunting, whinchat and yellow wagtail.

By June the richer meadows are a blaze of colour as traditional flowers reach full bloom. Pools and ditches hold large numbers of invertebrates, including 59 species of water beetles. Look out for the spectacular raft spider that has a 4 cm body and even longer legs and walks on water to catch its prey. The Levels are famous for dragonflies, the most charismatic of which is the hairy dragonfly, a beautiful blue and gold hawker which patrols flooded peat workings and ditches. Rare marsh fritillary butterflies also breed and grasshoppers and crickets abound.

In Summer kestrels hover overhead and in the long, light evenings barn owls haunt the reed-beds. Garganey, our only summer visiting duck, can be found on the pools. Recently a flock of little egrets has frequented the area - a new addition to the local birdlife.

Winter is another prime time to visit the area, as hunters such as short-eared owl, Merlin and peregrine patrol open ground. Shallow standing water and abundant soil invertebrates attract large flocks of waders and wildfowl, including wigeon, teal, Mallard and Pochard, together with gadwall, pintail, shoveler and tufted duck. The wet moors are important for wintering flocks of Bewick's, mute and whooper swans. Bittern, bearded tit and Cetti's warbler all overwinter here.

Shapwick is well worth a winter visit to see the starling roost. Six million starlings roost in the reedbeds each year and the pre-roosting flocks are the largest and most spectacular in Britain. So many birds cause extensive reed flattening and damage but the aerial display is breath-taking.

Where to go
Swell Woods Rspb Reserve (ST 360238)
Swell Woods has the largest heronry in the South West, with more than 100 pairs most years. A public hide in the wood (open at all times) allows visitors to watch the breeding birds. Heron courtship begins very early (January or February), long before the trees come into leaf, and great views are possible. In winter the RSPB provides food for small birds and the car park is a great place to get close views of tits, nuthatches and jays.

West Sedgemoor Rspb Reserve (ST 361258)
The large RSPB reserve at West Sedgemoor (adjacent to Swell Woods), is made up of small, low lying fields and meadows separated by narrow water-filled ditches. It is one of the most important spring passage sites for whimbrel in Britain, and one of the richest for breeding waders in SW England. Large numbers of wintering birds visit and feed on the moor including lapwing, snipe and Bewick's swans.

In spring huge numbers of migratory warblers arrive. 200-odd pairs of sedge warblers set up territories on the moor. Drumming snipe can be heard, and sometimes seen, on warm, drizzly mornings. Listen too, for nightingales, which breed in thick hedgerows along the south droves.

The meadows have a diverse flora including meadow rue, meadow thistle, marsh arrowgrass and marsh ragwort. Marsh marigolds and cuckoo flowers are spectacular in May. The ditches also contain a rich flora including locally rare species such as the flowering rush, frogbit and fine-leaved water dropwort. They are home to a rich invertebrate fauna including scarce water beetles, dragonflies and bugs.

Shapwick Heath English Nature Reserve(ST 465388 )
This reserve includes Westhay, Catcott and Ham Wall. Since 1993, 6000 hectares of peat workings at Shapwick have been converted back to reed bed, meadow and woodland by English Nature. Access is easy, and good viewing is possible from an old railway embankment that runs through the middle of the reserve.

Shapwick is a great place to hear the dawn chorus. The mosaic of habitats means woodland and wetland species sing together - seven or eight species of warbler at once. Reed warblers are particularly common so it is not surprising that there are lots of cuckoos in the area. In May they call all day long.

This is one of the best places to see large congregations of hawking hobbies - especially in May when up to 50 hunt together. Their prey includes the Hairy Dragonfly.

Near the entrance to the Reserve is a pool full of introduced marsh frogs which sing loudly on bright mornings. Encouraging bitterns back to breed is a major project at Shapwick. They have not obliged yet but are seen here occasionally

Pole nest-boxes occupied by barn owls are positioned along the old railway and in the evening owls are commonly seen sweeping over fields and reed-beds. Bill watched "swamp badgers" here. Some of the setts are dug very close to water and badgers are occasionally encountered on paths through the reeds.

Westhay Moor nnr (ST 457438)
An area of tall fen vegetation with scrub, marshy grassland ditches and small pools right in the heart of the peat moors. The reserve owes its existence to exhausted peat diggings that were left to flood and regenerate. The open water, reed beds and scrub attract a wide variety of wetland birds. Westhay supports a nationally rare fen community, including a wide range of breeding and wintering birds.

This is the only Somerset site where the nationally rare marsh harrier breeds. In addition, the fens support breeding populations of many other bird species, including: little grebe; Cetti's warbler; whinchat; water rail, mute swan; reed warbler, sedge warbler and teal. The area is also frequented by kingfisher, buzzard and grey heron. Harvest mice breed at Westhay and otters are regularly seen on the Heath.