Most of the hides look out over the estuary, so what you see depends on the tide. It's not the most bird-packed part of the Mersey, but good numbers of gulls are present and smaller numbers of waders. I see peregrine there quite regularly too. the feeding stations attract a typical range of woodland birds, but its also a good area for bullfinches.
If you walk right to the end of Wigg ther's a Tower Hide overlooking Astmoor Lagoon and the adjacent saltmarsh. There's also a feeding station behind the Tower which has supported willow tits all winter. A scope is pretty much essential for viewing the lagoon, but its the best area at Wigg. A good variety of widlfowl are usually present in the spring, and there there water rails, grasshopper warblers and sometimes Cetti's warbler there too. Little egrets are pretty regular and I've seen hobby, garganey and greenshank there. I've always thought it an underwatched place, but the difficulty of viewing the best areas probably puts people off. The saltmarsh turns up regular merlin and short-eared owl, but of course is best in the winter for these. In the summer there are breeding lapwing and sometimes redshank.
Hope that helps.