And to close up shop on C24...
I spoke to Harry Lumsden today, who confirmed that the bird is indeed a trumpeter swan, but perhaps more interestingly, that bread is a perfectly good food for swans to eat! I shall never again let my thoughts turn murderous upon sight of a swan-feeding bread person!
Thanks again to everyone for their help. It was a true pleasure talking with Harry, by the way. Funny, engaging, and knowledgable, to say the least...
All the best,
David