The avifauna of Bermuda include 408 species, according to the Bermuda Audubon Society (BAS), with some additions from Clements taxonomy, as of July 2022. The 387 species is a remarkable number considering that the island is a mere 53.3 square kilometres. (Additional species known only from the fossil record or speculatively from the time of early exploration are not included.) Ten species were introduced by humans; the mallard also occurs naturally as a non-breeding migrant. Of the 408, 104 are uncommon, 61 are rare, and 152 are very rare, all as defined below. Audubon's shearwater formerly bred in Bermuda but is now only a vagrant; All endemic species are considered extinct. Audubon's shearwater formerly bred in Bermuda but is now only a vagrant; Eskimo curlew is considered extinct.