The 2nd batch of bluebird eggs were due to hatch this past Friday June 8, I checked today and they haven’t hatched yet. I’m guessing they may possibly be infertile? The female has been incubating them and they had fledged 4 healthy babies from the 1st nesting so I’m a bit puzzled. Could this be another pair of bluebirds nesting in my nestbox and that are infertile?? Thanks!
Have you checked to see if the eggs are being turned or rotated? You just put a magic marked bleck dot on each egg and then check the next day to see if parents have rotated them, meaning the dot should be in different position. If she is still incubating I would do this -if she is not they probably are not good, but need to leave them alone for a while. 4 days overdue is quite a bit, but a lot could depend on the weather.