Known as the first and oldest Citizen Science project, at over 115 years, Audubon’s Christmas Bird Count is also one of the largest, with 70,000+ person-days of efforts and more than 64 million birds counted each year. The CBC has contributed greatly to the science of bird conservation with hundreds of publications, including many in important scientific journals. From December 14 through January 5 each year, tens of thousands of volunteers throughout the Americas take part in an adventure that has become a family tradition through the generations. Count volunteers follow specified routes within a designated 15-mile diameter circle, counting every bird they see or hear all day, and submit data to each circle compiler. 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. If observers live within a CBC circle, they may arrange in advance to count the birds at their feeders and submit those data to their compiler. All individual CBCs are conducted in the period from December 14 to January 5 (inclusive dates) each season, and each count is conducted in one calendar day (24-hour period). As featured in Chapter 2 of Citizen Science by Caren Cooper.