Each species on the British List is placed in one or more categories denoting its status on the List.

In 1997, categorisation was revised to assist protection under national wildlife legislation, especially of naturalised species. Category C was expanded to allow species with different histories of introduction and naturalisation to be distinguished; Category D (not included in the List totals) was reduced in scope, and a Category E (not included in this list) was introduced to enable local and national recorders to monitor escaped species.

Category A
Species recorded in an apparently natural state at least once since 1 January 1950.

Category A species contained in the main list here

Category B
Species recorded in an apparently natural state at least once between 1 January 1800 and 31 December 1949, but have not been recorded subsequently.

Category B species contained in the main list here

Category C
Species that derive from translocation(s) (i.e. human-mediated movement and release (IUCN/SCC 2013)) resulting in the establishment of self-sustaining populations within Britain, and vagrants from self-sustaining populations outside of Britain which have derived as a result of translocation(s) (McInerny et al. 2022).

• • C1 – Naturalized translocated species – species that have occurred only as a result of translocation(s), e.g. Red-legged Partridge Alectoris rufa
  • C2 – Naturalized established species – species with established populations resulting from translocation(s), but which also occur in an apparently natural state, e.g. Greylag Goose Anser anser
  • C3 – Naturalized re-established species – species with populations successfully re-established in areas of former occurrence following a conservation translocation(s), e.g. Red Kite Milvus milvus
  • C4 – Naturalized feral species – species which have been domesticated which now have populations established in the wild, e.g. Rock Pigeon (Dove)/Feral Pigeon Columba livia.
  • C5 – Vagrant species from populations outside of Britain which derive from translocation(s).
    • C5.1 A vagrant from a re-established population – individuals from a population established from a conservation translocation(s) in order to re-establish a species within its former range but for which there is no evidence of Britain being part of its former range. Currently, there are no species in C5.1, but Bearded Vulture Gypaetus barbatus for example may become eligible in the future, if the European population becomes self-sustaining and vagrants derived from this population appear in Britain.
    • C5.2 A vagrant from a naturalized population – individuals from established naturalized populations outside of Britain that are a result of translocation(s) and that are outside the normal range of the species, e.g. possibly some Ruddy Shelducks Tadorna ferruginea occurring in Britain originating from naturalized populations in near Europe. Currently, Egyptian Goose Alopochen aegyptiacus is the only species in C5.2.
  • C6 – Former naturalized species – species formerly placed in C1 whose naturalized populations are either no longer self-sustaining or are considered extinct, e.g. Lady Amherst’s Pheasant Chrysolophus amherstiae, currently the only species in C6.

  Category C species contained in the main list here

  Category D
  Species that would otherwise appear in Category A except that there is reasonable doubt that they have ever occurred in a natural state. Species placed in Category D only form no part of the British List, and are not included in the species totals.

  View Category D species

  Category E
  Species recorded as introductions, human-assisted transportees or escapees from captivity, and whose breeding populations (if any) are thought not to be self-sustaining. Species in Category E that have bred in the wild in Britain are designated as E*. Category E species form no part of the British List (unless already included within Categories A, B or C).

  View Category E species

  Category F (list being compiled)
  Records of bird species recorded between c. 16 000 BP (before present) to 1800.

  • F1 – Records of bird species recorded between c. 18000 BP (before present) to 1800
  • F1.1 – 1500 – 1800 – Post Medieval
  • F1.2 – 1100 – 1500 – Medieval
  • F1.3 – 400 – 1100 – Early Medieval
  • F1.4 – 0 – 400 – Roman/Iron Age (Scotland)
  • F1.5 – c. 3500 BP – 0 – Iron Age
  • F1.6 – c. 45000 – c. 3500 – BP Bronze Age
  • F1.7 – c. 6000 – c. 4500 – BP Neolithic
  • F1.8 – c. 11000 – c. 6000 – BP Mezolithic
  • F1.9 – c. 18000 – c. 11000 -BP Late Glacial
  • F2 – 16000 bp back to early Pleistocene c.2.58 MaBP
  • F3 – Uncertain species or date

  Each of the above can be further subdivided to denote (a) fossil or bone specimen and (b) documentary only records, e.g.

  F1.1a = A fossil or bone specimen record from between 16000 BP to 1800 AD

  F1.1b = A documentary only record from between 16000 BP to 1800 AD

  A species is usually placed in only one category, but some are placed in multiple categories, for example, those species occurring in Category A which now have naturalised populations (e.g. Red Kite).

  Category F is currently under construction.

  The British List comprises only those species in Categories A, B and C.

  The newly created Category C6 recognises that some previously established naturalized introductions to Britain have declined (and others may do so in the future) to a level that is no longer self-sustaining, and which will ultimately lead to extinction. Further releases of such non-native species are prohibited under Section 14 of the Wildlife & Countryside Act 1981.