Pied wagtail  (Motacilla alba )

Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

1. National Biodiversity Network Species Dictionary (January2004):
   http://www.nhm.ac.uk/nbn
   
2. Mullarney, K., Svensson, L., Zetterström, D. & Grant, P.J. (1999) Collins Bird Guide. HarperCollins Publishers Ltd, London.
   
3. RSPB A-Z of Birds: Pied wagtail (February 2004):
   http://www.rspb.org.uk/birds/guide/p/piedwagtail/index.asp
   
4. British Trust for Ornithology/ JNCC- breeding birds in the wider countryside: pied wagtail (February 2004):
   http://www.bto.org/birdtrends
   
5. Lack. P. (1986) The Atlas of wintering birds in Britain and Ireland. T & A D Poyser Ltd, London.
   
6. Holden, P. & Sharrock, J.T.R. (2002) The RSPB Guide to British Birds. Pan Macmillan, London.