11.30 a.m.: In the woodland glade of the Menagerie at Nostell one nuthatch is chasing another. 
There’s an exchange of ‘tickety-tick’ type calls followed by a high-pitched repeated ‘Chuieee’ call.
What I take to be the male bird is posturing, following the female from tree-trunk to the bough of the neighbouring tree.
In subdued winter plumage, the yellow on the breast of a grey wagtail is a good match for the buff colour-wash on the buildings of the stable block that overlook the walled garden.
The bank behind is steep and covered with brambles and there are no midstream rocks to perch on so their technique involves at lot of hovering over the water surface.