A few years back, I put a nestbox on the apex of my garage. I placed it so that I could watch the comings and goings from my kitchen window. It took a year or two before the birds showed and interest in it, but one spring a pair of blue tits nested in it. I was fortunate to watch them coming back and forth with food for the young ones.
I was fortunate enough to see the adults coming to the nestbox with caterpillars and other grubs. The above image is one such occasion. The adults always looked round as if they were checking to see if there was anything that could see them going into the nest. This gave me the opportunity to capture an image with them looking straight into my lens.