This species is a rare, nearly annual spring migrant with most birds arriving during the second half of May. As with all waterfowl, swans will occasionally linger for long periods (up to five months in one case) with all but one of the summer and early fall (pre-October) records being accounted for by lingering birds from the spring. As a late fall migrant, this species is unlikely to be encountered arriving before late September or October with all known arrivals during the month of October. Both winter records are simply early spring arrivals from April, though it is certainly possible for individuals to arrive earlier in late winter or to linger late into the fall and winter in years when open water allows.
Nearly all records pertain to the American subspecies columbianus, but the Asian subspecies bewickii (Bewick’s Swan) has been recorded in the Pribilofs very rarely. It can be identified from the American subspecies by the more extensive yellow at the base of the bill, which is rounded or squared off; this distinguishes it from the Whooper Swan, which has even more extensive yellow that ends in a point.
