Nest-building!

I sat by this puddle, foot resting and waited 30 minutes for this blip of a Swallow that will not stop hardly ever ;-) it scooped up a bit of dried grass and covered it's beek in mud! on closer inspection I realised that it must be collecting this to build a nest? You will need to look large to see the detail.
Thank you for all of your lovely comments on my yellow and green field yesterday ;-)