The Christmas Bird Count is the longest running community science project in the nation. Birders, from beginners to advanced, have participated in this once-a-year count effort within established 15-mile diameter circles (see maps). Compilers and participants work together to ensure that important bird habitats are covered, and there is always room to add yard and local patch observations, so long as the number of people observing and the time spent observing are recorded, along with a full list and numbers of all species observed. Los Angeles Audubon Society sponsors three counts, led by experienced compilers.