Nice shot! Ours didn't nest this year, although they have been visiting. There is a Blue Jay nearby that has been raiding the nest, which may be why it is empty.
I went to a tree the other day in a park that has always had tree swallows in it and was hoping to get tons of shots but there wasn't a single swallow around. I don't know if they had already nested and gone or what the reason was. I did get some shots of seagulls and Canadian Geese and had a great time at the Park so all was not lost.
Now you have me thinking of going to a farm down the road to try to get pics of barn swallows.