Nocturnal Bird Call

• These birds call from sunset to sunrise right through and have been calling (it seems) to one another from trees in farmland in Northern Ireland. This is in Summer (July). In the twilight I have seen one flying and it seems a rather large bird with a light underside. 

I am so curious to know what they are

3404.Bird Call.m4a

7206.Bird Call 2 .m4a