The United Kingdom is situated off the northwest coast of Europe (and the Western Palearctic biogeographical region, or ecozone) and is surrounded by the Atlantic Ocean to the west and the North Sea to the east, with the English Channel to the south (broadly speaking). Most of the United Kingdom has a temperate climate, generally cool with much year-round rainfall, though some areas (such as the very high mountains in Scotland and the westernmost areas) do have different climates (e.g. subpolar oceanic, continental subarctic, and tundra climates). The United Kingdom experiences four seasons, spring, summer, autumn, and winter.
With the prevailing wind coming from the southwest, the western side of the United Kingdom is wetter than the eastern side. Atlantic currents, warmed by the Gulf Stream, bring mild winters particularly to the west, however, the north and east of the United Kingdom can experience cold winters when weather systems open up airflow from eastern Europe and Siberia. Arctic blasts from the north and Mediterranean blasts from the south can occur in winter and spring, and during the autumn period hurricanes can hit (usually the tail end of hurricanes that have come across the Atlantic Ocean). All of these factors lead to the United Kingdom being great for birds from different areas of the world all through the year.
An increasing number of people are interested in nature and specifically in birdwatching as evidenced by the fact that the United Kingdom’s number one birdwatching charity, the Royal Society for the Protection of Birds (RSPB), has over one million members. Many towns, cities, and regions also have their own bird clubs or societies, with social birding a big hobby. Technological advances have furthered the work carried out by the British Trust for Ornithology (BTO), and eBird is increasingly widespread, furthering the value of citizen-science birdwatching. Incredibly over 620 species of bird have been recorded from the United Kingdom, the vast number of these being vagrant birds. Twitching is a very popular hobby within the realm of birdwatching, as is bird photography. “Bird news” is a very important way of birders finding out about rare birds, and websites like BirdGuides, Rare Bird Alert, and Surfbirds have all helped with the flow of bird-sighting news and undoubtedly increased the number of people interested in birds and birding. There is currently only one widely recognized endemic bird in the United Kingdom, the Scottish Crossbill, although some authorities do consider the subspecies of Willow Ptarmigan known as Red Grouse to be another endemic. About 250 species of bird occur frequently, and tours during the spring and winter periods can connect with a good percentage of these.
What is clear is that given its location, given the climate and weather conditions often experienced, given the migratory nature of a huge number of birds, and given the large number of people interested in the hobby (or sport!) of birdwatching it is no wonder that the United Kingdom is a great place to go birding year-round.