I have a pair of mute swans on my pond. They are about 20 years old, and for the first 16 years or so they produced offspring. Recently though their eggs don't hatch. They are sitting on several obviously lifeless eggs right now. They've been doing this for at least twice as long as a successful episode would require.

Is there something I should do to get them to abandon the nest? I removed the eggs last year after it was obvious none would hatch, but they laid more eggs! I assume nature will dictate when they should "move on", but I'm worried that they aren't eating enough and getting enough exercise, being on the nest for so long. The female, in particular, looks very scrawny now.

Any wisdom would be greatly appreciated.