As nature comes in an infinite variety of forms, so too did the design work inspiration. Some of the work merely reproduced flora and fauna in its natural setting, or at least as natural as the decorative piece could allow, while other work used much more of a stylised effect in order to produce an all over pattern that would appear to be optically motivated while at the same time still being based on the natural world.
Swans were a particular favourite as they were considered to be both majestic and elegant and by their very nature were also, with their long sinuous necks, a perfect example of an animal made for instant duplication and involvement within the exaggerated sensuous swirls and tendrils that were the hallmark for so much of the Art Nouveau decorative style.
There seemed to be less of an inclination to incorporate swans into all over pattern work, and much more that of placing them within an elegant border as if they were somehow aloof from the everyday design work and more attuned to the specialised areas of decorative design, as you would expect any self respecting swan to be of course.
It is perhaps misleading to see the swan as a major decorative effect within the Art Nouveau movement. There were after all many other motifs that were much more popular, such as the dragonfly, but it is still an interesting design mechanism that has been used throughout the history of decorative design work, and revealing the swan in only one of its many incarnations over the centuries is still worthy of notice.