Most birds spotted in one year (individual)

The most bird species observed in the field by an individual in one calendar year is 6,852 by Arjan Dwarshuis (Netherlands) in 2016. This tally represented about two-thirds of all known bird species at the time. During his "Big Year", Dwarshuis raised funds for BirdLife International.

Owing to ever-changing taxonomic developments, the total has now risen to 6,910 species (as of December 2021) but 6,852 was the number as it stood in 2016, so that is the given record.

In the same vein as "Big Days" (a birdwatching challenge to identify the most bird species within a 24-hour period), a “Big Year” is a personal effort, usually by individual birders, to identify as many bird species as possible during a single calendar year. Many birders restrict their Big Year efforts to a certain geographic area, such as a country or continent, but in Dwarshuis' case he visited 40 countries across six continents (all bar Antarctica).

As with most aspects of birding, accumulating a list of species seen or heard fundamentally depends on an honour system. Whether birding only casually for an hour or two, or participating in officially sanctioned birding competitions, experienced birders recognize that it is vital to tally only those species that they identify positively and without doubt. To encourage adherence to the honour system, and to standardize practices that ensure comparability among birding practices of different teams, the American Birding Association, among others, have developed official rules by which an officially registered Big Day Count must be conducted.

While the notion of "Big Day" bird counts date back to the late 19th century, one of the pioneers of logging species over a year was American businessman Guy Emerson. In 1939, he observed 497 species during his travels around North America; this record lasted until 1952 when Bob Smart raised the bar to 510 species; this only stood for one year, though, as in 1953 American ornithologist Roger Tory Peterson documented 572 species.

Dwarshuis used the IOC World Bird List as his checklist, which does recognize more species compared to the more traditional Clements Checklist; nevertheless even taking this difference into account, he still achieved a higher count than the previous record.

This bettered the mark of 6,042 (or 6,153 species based on the IOC World Bird List) set only a year earlier by Noah Stryker (USA), who in turn surpassed a 2008 record of 4,341 set by British birders Ruth Miller and Alan Davies.