‘… the whippering cries of golden plover.’

This seems to be a Williamson coinage to describe the cry of a bird.  I haven’t found it in the Big Fat OED, source of all (English) words.  See also ‘stitter’ and ‘chitter’.

Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 109