I have asked this question before but no one deemed to answer me so I thought I would try again.
My father has had swallows nesting in his shed for over 40 years and wonders if they are from the same family or just swallows passing through who spot his shed and decide to build a nest. They have to duck through a low doorway to get up to the rafters so it is not an easily accessed spot to build a nest. I am pretty sure they often use the nests that are there too.
Any insight into swallow behavior would be nice.