Quick comment:
How about something like this? Assign an Individual ID to the bird that build the nest which would be an Occurrence (documentary evidence of the bird that built it). Assign an Individual ID to the brood-parasitic bird that laid the egg in the nest which would also be an Occurrence. Use the DwC Resource Relationship terms (http://rs.tdwg.org/dwc/terms/index.htm#ResourceRelationship) to define the parasitism relationship between the two Occurrences. This would be a good opportunity for John to demonstrate how one does this - I've never been clear exactly how it is supposed to work.
I had originally assumed that the objects of interest were the eggs from two different species of birds, aggregated into a single nest. If that's the case, then I think how I described it is appropriate. But I also think what Steve describes above is appropriate, if that's a better context for how the record should be represented.
Aloha, Rich