The chalk cliffs are mainly sheer with little vegetation, but the…

The chalk cliffs are mainly sheer with little vegetation, but the sandstone cliffs are more tumbled with an undercliff structure, and in places of sufficient stability to have allowed vegetation to form.
All these cliffs erode rapidly and retreating at a rate of up to 1.86 metres per year.
Large single falls are less common on the sandstone cliffs than on the chalk and the former tending to slump and yet recede the fastest.
The birds regularly recorded nesting on these cliffs are the Kestrel, Herring Gull, Jackdaw, Rock Pipit, Starling, House Sparrow and Stock Dove.
Lesser Black-backed Gulls nest on the cliffs periodically, as do Black Redstarts. Fulmars have bred and have been present since at least the early 1950s. House Martins have been recorded nesting on the cliffs occasionally.
Cormorants no longer breed, and the Raven has not nested since 1895, apart from a pair, one bird at least of which was an escaped pet, which nested between 1938 and 1945.
The Peregrine Falcon has not bred since 1957, although the chalk cliffs once held one of the highest densities of breeding pairs in Britain.
The cliff-nesting Kestrel population had probably declined by the late 1940s, and certainly did so after 1951.
A reduction in suitable nest sites has been suggested as a possible cause, and a breeding survey of cliff-nesting Herring Gulls and Rock Pipits conducted in 1965 tends to confirm this idea.
This survey showed three pairs of Rock Pipits nesting in the cliffs east of Hastings, and 42 pairs on the chalk cliffs.
Although no Herring Gulls were reported nesting on the Hastings cliffs up to 1935, a total of 371 pairs did so in 1965 compared with 395 pairs on the chalk cliffs.
However, Walpole-Bond in 1938 recorded “perhaps as many as 2,000 couples” of Herring Gulls between Seaford and Beachy Head alone and and since it is doubtful whether there are suitable sites for this number at present, a change in cliff structure along the chalk is very likely. Probably some of these birds moved east to the sandstone cliffs. Tidal Basins and Mudflats, Estuaries and Saltings
Tidal mudflats occur at the mouths of nearly all Sussex rivers, along the coast principally at Pevensey Bay and from Pett to Rye Bay, and most notably in the tidal basins of Pagham and Chichester Harbours.
Chichester Harbour straddles the county boundary with Hampshire and the harbours of Langstone and Portsmouth (also Hampshire) are a part of the same ecological and physical unit.
Chichester Harbour alone has some 1,298 hectares of mudflats, 164 hectares of sand, 611 hectares of Spartina marsh, and 42 hectares of saltmarsh.
For reasons of simplicity (and ornithological necessity) the whole of Chichester Harbour is considered as being within Sussex for the purpose of wildfowl and wader counts.
Breeding bird species of these largely intertidal habitats are, not surprisingly, few, although some, particularly Redshank and Meadow Pipit, nest on the drier parts of the saltings with a few Lapwings.sizeable gull and tern colony exists on islands in Chichester Harbour.
The most important species nesting in close association with tidal areas is the Shelduck which nests around Chichester and Pagham Harbours, near the Cuckmere River, at Pett Level and in the Rye area.
No full census of the breeding numbers of this species has been carried out recently, but there are probably some 100 to 150 pairs.