The river Teign near us is home to sand martins, they are usually the first to arrive, before the swallows. It grieves me (but probably not the birds!) that sections of the bank give way each winter, destroying nesting holes.
I imagine them almost in sight of "home", wings aching with tiredness, saying to each other..nearly there dear, I'll get the kettle on.... and arriving to find their home gone. They soon set to though and make another!