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What is the Christmas Bird Count (CBC) anyway?
The National Audubon Society Christmas Bird Count (CBC)
is an early-winter survey of birds. The CBC is a 2-week period of time (around
Christmas) where birders across the country spend (at least) 8 hours in a single
day (in a specially designated area assigned to them) counting the birds and
species they encounter. How is works is that a person looks at a "group"
of birds for a couple minutes and "counts" the numbers in the species. It
is better if two (or more) people are together looking at that same group of
birds and counting so that a consensus can be reached, but one will do.
Any number of people that go out counting in a single area are considered a
"group" (from 1-100). Although counts occur in Central and South
America, most CBCs occur in North America. The sample area for a count is a
circle that is 15 miles in diameter, and varying numbers of volunteers
count all birds they see in the circle during a single day, which is within 2
weeks of 25 December. (Butcher 1990) Although
this analysis only considers the interval 1959 - 1988, the CBC was begun in
1900. The number of circles and participants has changed dramatically since the
early years. Butcher (1990) notes that 1,508 circles were surveyed in 1986-1987.
Audubon.org CBC information
History of the Christmas Bird Count |
