Is It A Bird?

This morning me and Phil both heard birdsong coming from the kitchen. It continued this evening. We've looked outside and can't here or see any birds and there is no bird trapped in any cupboard. There is a tiny vent but surely one can't have flown in there (being as wide as my little finger). We've called the "bird" Ruud because it is a rude bird always interrupting our conversation and we'd just played as Holland on PES6. More updates if the chirping continues!