The Christmas Bird Count is a long-standing program of the National Audubon Society. It is an early winter bird census, where volunteers follow specified routes through a designated 15-mile (24-km) diameter circle, counting every bird they see or hear all day. It's not just a species tally-all birds are counted all day, giving an indication of the total number of birds in the circle that day. All individual CBC's are conducted in the period from 14 December to 5 January (inclusive dates) each season, and each count is conducted in one calendar day.
Big Bend National Park holds two bird counts annually in the week between Christmas and New Years day. One focuses on a circle in the Chisos Basin, the other in the Rio Grande Village area.
