Linda, I have my doubts about this pair breeding this season. The optimal time for laying eggs and successfully raising a family has passed. The female seems not to act "broody" at all. Normally, based upon our observations over the years, we would expect her, once she is carrying a fertilized egg, to spend much time in and on the nest for several days before the egg is laid.
The timing of the breeding season must be embedded in their genes. They must get their young flying out and about before the worst heat of the summer, as fish are harder to catch the warmer the water gets. Then the young must be old enough to migrate north for cooler water before the end of June.
Young and inexperienced birds of many species are know to have difficulty with their first clutch of eggs.
They are now two months behind schedule. I could be wrong, of course, as there is the potential for variability in all natural creatures.