Question Author
Thank you all for your observations. We are upset about this current stand-off because 'our' pair of swans have been almost like members of our family for years.
The male comes up to our back door on a regular basis, knocks on the glass with his beak and, if we don't answer to feed him, he then walks around to our patio window and knocks on that in an attempt to raise us. His mate is more timid but she also spends a great deal of her time in our garden.
When their cygnets hatch (their nest is in a garden a few houses away) they bring the new brood to show them off to us. When one of their 2009 brood of four was injured in November, we called the RSPCA and the bird was taken away to a sanctuary in Essex for treatment & care.
I don't know how long swans live but you can understand how protective we feel about Gregory & Ziggy.