In confirmation of the comment by Ian about House Martins I too had noticed the marked absence of birds -- that was up until today when a large flock - 50+- were in a feeding frenzy over our fields, nr Bow Street late this afternoon.
Another notable sighting today was of a Kingfisher on the lower Ystwyth nr Llanfarian. Numbers had dropped considerably after the hard winters of 2011, 12, 13.