“Swan, (lat. cygnus, fr. cygne): this graceful bird has for various reasons been a favourite charge in armorial bearings. Swans are generally blazoned as proper, i.e. white, else they are described as argent, but they are frequently beaked and legged of other tinctures. The bird is generally borne with expanded wings, and it seems desirable that the position should be noticed, though as a fact it is only seldom so. Sometimes they are drawn swimming towards each other, and for this the word ‘respectant’ or ‘incontrant’ seems to have been used by some heraldic writers.”
“The Cygnet sometimes occur; and a cygnet royal implies a swan gorged with a ducal coronet, having a chain affixed thereunto and reflexed over its back. It should rather be blazoned a swan proper, ducally gorged and chained or, a cygnet being properly a young swan. It was one of the badges of Henry V. The term, however, may properly be used when there are two or more swans in one coat, like lioncel.”
Source: Swan in Parker’s Heraldry (1894)