Thank you for your reply!
I wish I knew if the formerly lone swan was male or female! That would definitely help in understanding what has gone on in this situation.
Do females ever leave and go in search of another mate if breeding is not going well with their original mate? Is it common for an adult swan of either sex to leave their family once the cynets are able to fly, which seems to be what happened here.
Also, can you shed light on the two nest situation and the abandoned egg in the first nest?
Many thanks – your expertise makes me even more in awe of these beautiful creatures!