The term birdwatching was first used in 1901; bird was introduced as a verb in 1918. The term birding was also used for the practice of fowling or hunting with firearms as in Shakespeare’s The Merry Wives of Windsor (1602): “She laments sir… her husband goes this morning a-birding.” The terms birding and birdwatching are today used by some interchangeably, although many participants prefer birding, both because it does not exclude the auditory aspects of enjoying birds, and because it does not have some associated negative connotations.

In the North America, many birders differentiate themselves from birdwatchers, and the term birder is unknown to most lay people. At the most basic level, the distinction is one of dedication or intensity. Generally, self-described birders are more versed in minutiae like identification (aural and visual), molt, distribution, migration timing, and habitat usage. Whereas these dedicated birders may often travel specifically in search of birds, birdwatchers have been described by some enthusiasts as having a more limited scope, perhaps not venturing far from their own yards or local parks to view birds.

Source: wikipedia.org