Hi,
Thanks, we did manage to take a peek last Friday when no one was home, and it was empty, just nesting material. I have built it so that I can open the roof for cleaning, etc. We did see both a male and female cowbird around that evening but we kept them away from the house. We were away for a few days this week so not sure what's been going on in our absence, but I went to check today and someone was home...
We've also got some robins nesting in a Blue Spruce near the house and looks like their eggs have hatched already as they have been busy feeding them. I guess Black Cap's lay their eggs later.
Cheers,
Mar