Without a camera inside NB1 its hard to tell if there is birds nesting inside, the only way we have found out is that theirs a tiny hole in the bottom on the nest box and you can see nesting material.

Recently i had a walk around where the nest box is located and i heard some birds chirping it was not until i got around 4 meters away that i could tell it was coming from the nest box.

I quickly grabbed my phone and started voice recording the nest box getting close but not to close where i was disturbing them. 

We are still unsure what bird could be nesting yet, we are working to try and get a camera inside NB1 for next year.