Birding or birdwatching is a hobby concerned with the observation and study of birds (the study proper is termed American origin; "birdwatching" is (or more correctly, was) the commonly-used word in Great Britain and Ireland and by non-birders in the United States. Since visual observation is routinely complemented with auditory observation, the term "birding" is more accurate, and is growing in usage, particularly among devotees of the hobby.
The most active times of the year for birding in the temperate zone are spring and fall migration, during which times the greatest variety of birds may be seen, as many species that do not nest in given areas may yet be observed in those areas as they make their way north or south.
Early morning is typically the busiest time of the day for birding since many birds are at their hungriest, and search most actively for food, and are thus easier to find and observe. Success in locating the more "interesting" species typically requires detailed knowledge of their appearance, sounds, behavior, and the most likely places to find them, in addition to good measures of stealth and patience.
Birding can be one of the quieter and more relaxed outdoor activities. However, some birders are keen rarity seekers and will travel long distances to see a new species to add to one of their "lists", e.g., life list, national list, state list, county list, etc. In Great Britain, these fanatical birders are commonly known by the light_hearted slang term of twitchers, from the frenzy that descends on some when they receive news of a rare bird. Some birders even compete in building the biggest species lists they can in their lives, a year, a day, etc. A North American one_day competition is called a "Big Day"; a British one, a "Bird Race". Teams trying to win such a competition or set the record for their area (such as a U.S. state) usually have to be in the field for twenty_four hours and drive many hundreds of kilometers.
Equipment commonly used for birding includes binoculars and a telescope with tripod, a notepad, and one or more field guides. Twitchers will also have a mobile phone and pager in order to keep constantly informed of rare bird sightings. Knowledge of the weather is also important, since the right winds can lead to drift migration.
Twitching is probably most highly developed in the UK, The Netherlands and Ireland because it is possible to reach any part of these small countries (including most islands) in a few hours, and their coastal locations add to the likelihood of rarities.
Prominent national organizations concerned with birding include the British Trust for Ornithology and the RSPB in the United Kingdom, and the National Audubon Society and American Birding Association in the United States. Many statewide or local "Audubon" organizations are also quite active in the US.
Birding is no longer perceived solely as a hobby, as many birders take part in censuses of bird populations and their migratory patterns, sometimes specific to individual species, sometimes counting all the birds in a given area, as in a Christmas Bird Count. This "citizen science" can assist in identifying environmental threats to the well-being of birds or, conversely, in assessing the outcomes of environmental management initiatives intended to ensure the survival of species known to be at risk or encourage the breeding of species for aesthetic or ecological reasons. This more scientific side of the hobby is an aspect of ornithology.
Increasing (seasonal) bird populations can be a good indicator of biodiversity or the quality of different habitats. Some species may be persecuted as vermin, often illegally (e.g. the Hen Harrier in Britain), under the (usually false) perception that predatory species increase in number at the expense of other species of birds, insects, or smaller mammals. In most cases, the reverse applies, that the population of predatory species is controlled by the abundance of the prey species. There are therefore scientific reasons for some bird counts in defined geographic areas.
Photography has always been a part of birding, but in the past the cost of good cameras and long lenses made this a minority, often semi-professional, interest. The advent of affordable digital cameras which can be used in conjunction with a telescope have made this a much more widespread branch of the hobby.