“Swan” is an older translation of the name of a bird listed among those unsuitable for food. The Hebrew term is more probably understood as a horned owl, water-hen, ibis, or another water bird rather than an actual swan.
The bird is mentioned in the lists of unclean birds in Leviticus and Deuteronomy.
Ancient versions identified the term variously as a purple water-hen or ibis. The Revised Version changed the identification to the horned owl. Swans do occur seasonally on the waters of the Holy Land, but their aquatic feeding habits do not fit the reason for placing a bird among abominations.