Christmas Bird Count

The world's longest-running bird count, going since 1900, and a sociable one. Each count happens on a single day between December 14 and January 5, inside a circle 15 miles across; a local leader called the compiler picks the day and organizes the volunteers, first-timers are often paired with experienced counters, and you can also count at a backyard feeder inside the circle. More than a century of the same method makes for powerful comparisons. Christmas Bird Count data has revealed dramatic declines in grassland birds, documented species shifting their ranges as the climate warms, and fed more than 300 peer-reviewed papers. Sign up with your nearest circle's compiler early, because participation has to be arranged in advance.