Accidental

A species that has appeared in a given area only a few times and whose normal range is in another area.

Compare it to casual.

Examples

 * Great Frigatebird, Chinese Pond-Heron, Grey Heron, Whiskered Tern, Stygian Owl, Eurasian Hoopoe, Mugimaki Flycatcher, Eurasian Blackbird, Grey Silky-Flycatcher and many others are accidentals to the United States.
 * Double-crested Cormorant, Redhead, Bald Eagle, Mourning Dove, Savannah Sparrow, Summer Tanager and many others are accidental to the United Kingdom.