San Diego County has one of the highest counts of animal and plant species that appear on the endangered species list among counties in the United States. Because of its diversity of habitat and its position on the Pacific Flyway, San Diego County has recorded the presence of 492 bird species, more than any other region in the country. San Diego always scores very high in the number of bird species observed in the annual Christmas Bird Count, sponsored by the Audubon Society, and it is known as one of the "birdiest" areas in the United States.
Try to answer this question if possible (otherwise reply "unanswerable"): What birding event does the Audubon Society host some years?
unanswerable