Are these migrants are White wagtails or Pied wagtails? or both are the same? or sub species?
From the Annotated Checklist, available here:
You will find:
White Wagtail Motacilla alba
- White Wagtail, M. alba alba
Very common migrant and winter visitor, mid-September to April.
- White Wagtail (Masked), M. alba personata
Uncommon migrant and winter visitor, 2 Sep to 13 Mar; regular through winter only at Wamm Farms; but withpassage noted elsewhere in early October.
Your birds are White Wagtail, M. alba alba