tundra swan; Bewick's swan; whistling swan
Refers to the species Cygnus columbianus, a migratory swan seen in Japan in winter. The name コハクチョウ is the standard Japanese common name.
In winter, tundra swans migrate to Japan.
I saw a flock of tundra swans at that lake.
Hiragana spelling is also used, though katakana is more common for species names.
Kanji form exists but is rarely used; the word is almost always written in kana.
Compound of 小 (ko, 'small') + 白鳥 (hakuchō, 'swan'), literally 'small swan', referring to its smaller size compared to the whooper swan.