In general the avifauna of Britain is, of course, similar to that of Europe, consisting largely of Palaearctic species. As an island, it has fewer breeding species than continental Europe, with some species, like crested lark, breeding as close as northern France, yet unable to colonise Britain.
The mild winters mean that many species that cannot cope with harsher conditions can winter in Britain, and also that there is a large influx of wintering birds from the continent or beyond.
There are about 250 species regularly recorded in Great Britain, and another 300 that occur with varying degrees of rarity.
About 120 species occur in the UK all year round. Some of these are permanent populations of sedentary non-migrants such as tawny owl or red grouse, whereas others have their numbers augmented by winter visitors from the continent (for example common starling), or depleted by winter hard-weather movements to Ireland or southern Europe (for example European goldfinch).
About 60 species are mainly summer visitors which breed in Britain but winter further south, mainly in Africa. A large number of these are insectivores such as warblers, flycatchers and common cuckoo, as would be expected from the scarcity of insects in British winters.
In 2007, 16 million birds flew from Africa to Britain. Swifts have declined 40% between 1994 and 2007. Nightingales are down 60% since 1994, wood warblers 67% down, turtle doves 66% down, spotted flycatchers down 59%, and cuckoos down 37%.
The mild winters make Britain attractive to about 60 species which breed further north. These are mainly larger birds, such as swans, geese, ducks, gulls and thrushes, but some smaller species, such as the snow bunting and brambling also arrive in large numbers.
The numbers of some eruptive species, like Bohemian waxwing, depend on food supplies and population numbers in their breeding areas.
Some species neither regularly breed nor winter in Great Britain, but pass through on migration often in large numbers. Arctic breeding waders are a good example, with species such as little stint and curlew sandpiper usually being fairly common on passage.
The numbers of some passage birds depend on weather conditions. There will be more Mediterranean visitors like hoopoes and Alpine swifts in spring if there are winds from the south encouraging an overshoot of the breeding areas.
Perhaps also best placed in this category are a few seabirds which breed in the southern hemisphere, but "winter" in the northern hemisphere during the northern summer. These are seen off the south west of Britain in autumn. They are the great shearwater, sooty shearwater and the rare Wilson's petrel.
One of the fascinations of the British list is the number of rarities. Because of its position on the western fringes of Europe, Britain receives a number of vagrants from North America. Some American gulls, ducks and waders are regular enough to not be considered rare. These include ring-billed gull, surf scoter and pectoral sandpiper. Rare American passerines include red-eyed vireo and blackpoll warbler.
Siberian species such as yellow-browed warbler and Pechora pipit also occur much more regularly in Britain than further east in Europe. This is because migrating birds are likely to rest on the well-watched eastern coast after crossing the North Sea.
Britain's climate militates against the profusion of introduced species that can be found in warmer places like Florida, but there are populations of nine self-supporting species that have been admitted to the British list. In addition, there are feral populations of Canada goose, greylag goose and other wildfowl which would be on the British list anyway through wild breeders or vagrants.
The introduced species admitted to the British list are:
- Egyptian goose, Alopochen aegyptiacus
- Ruddy duck, Oxyura jamaicensis
- Mandarin, Aix galericulata
- Red-legged partridge, Alectoris rufa
- Golden pheasant, Chrysolophus pictus
- Lady Amherst's pheasant, Chrysolophus amherstiae
- Common pheasant, Phasianus colchicus
- Rose-ringed parakeet, Psittacula krameri
- Little owl, Athene noctua
- The Tablet, page 27, 25 April 2009, "Spring song diminuendo", a review of the bookSay Goodbye to the Cuckoo by Michael McCarthy