Each year jackdaws set up a nest in one of our chimney pots. They did it again this year and the young fledged around end April. Since then almost every day the jackdaws return to the pot - about 4 or 5 of them. Two of them will dance around the rim of the pot quivering their tails, looking in the pot. Then one of them will jump back into the pot and out. We have not seen this in previous years. Why have they returned to the nest pot, why do they do that quivering dance?