Maybe they roosted somewhere nearby and were feeding up this morning before heading south?

we have had House Martins breeding in our cul de sac for the last 15 years , apart for the last two years when we have had a no show due to falling numbers , woke this moring to have 50+ buzzing around the area , surely its to late to breed ? They is a lot of activity , also noticed good numbers yesterday on Deane Rd at work .Any ideas