We've had House Sparrows returning to nest for past couple of years, in a small hole in a building just under the gutter. However this year Starlings came and tried to take over the nest. A little while later, what looks like a piece of loose brick has wedged into the entry of the nest. The House Sparrows set up a new nest close by, as did the Starlings, but now the Starlings (with fledged chicks) have returned and are trying to get into the blocked nest, along with a male House Sparrow (the same male that is entering the new Sparrow nest). Yesterday the male House Sparrow did manage to get into the blocked nest, but it was tight, he was then outside pecking at the stone/brick. Why are they all trying to enter this old nest? Any information would be a great help, thank you in advance!