We have a Bluetit nest in a box on one of our garden sheds and two adults have been very busy feeding some noisy chicks for a couple of weeks now. Alternating between taking in fat from fat balls on one of our feeders and going further afield to bring back what looks like small green caterpillars from the park. About 3 days ago, a 3rd Bluetit has appeared and is also taking food into the nest box. It looks fully grown, but when waiting to go in, it flutters its wings like a young bird does when wanting fed. The other two birds seem quite at ease with this one, but is this normal, or is it an earlier fledgling helping out?