Birds are a group of warm-blooded vertebrates constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds.
Birdwatching, or birding, is the observing of birds, either as a recreational activity or as a form of citizen science. A birdwatcher may observe by using their naked eye, by using a visual enhancement device like binoculars or a telescope, by listening for bird sounds, or by watching public webcams.
Most birdwatchers pursue this activity for recreational or social reasons, unlike ornithologists, who engage in the study of birds using formal scientific methods.
Birding as a competitive event is organized in some parts of the world. Such competitions encourage individuals or teams to accumulate large numbers of species within a specified time or area with special rules. Some birdwatchers will also compete by attempting to increase their life list, national list, state list, provincial list, county list, or year list. Such events have been criticised, especially those claimed to aid conservation when they may actually mask serious environmental issues, or where competitive birding involves large amounts of driving. The American Birding Association was originally started as a club for "listers", but it now serves a much broader audience. Still, the ABA continues to publish an official annual report of North American list standings.
Competitive birdwatching events include:
Big Day: teams have 24 hours to identify as many species as possible.
Big Year: like a big day, but contestants are individuals, and need to be prepared to invest a great deal of time and money.
Big Sit or Big Stay: birdwatchers must see birds from a circle of prescribed diameter (e.g.: 17 feet[49]). Once birds are spotted, birdwatchers can leave the circle to confirm the identity, but new birds seen may not be counted.
