Tree Swallows are one of my big frustrations. Some birds are hard to photograph because they are elusive. Not so here. At times these swallows pose nicely. But still, dark iridescence blue, black, bright white, etc.
I moved around the nest boxes and shot from every side and background. These are the best I could do.
Unless there is perfect light (and I have been luck in the past) the birds natural shadows and contrast will drive you crazy.
I still stop by the area pretty often since they are still fun to watch and I might get the perfect light again.