1) I can't help you in this particular situation, but maybe the link below can assist you in field/photo identification of certain swallow species in the future. The text also mentions calls of swallows/martins, and I also think they are very useful to know, at least in Europe.
2) Do you regularly use binoculars while looking at birds, or do you typically observe them with the naked eye (there are different preferences among birdwatchers)?