House building?

Last year a pair of House Martins partially built this nest, but didn’t use it. We thought perhaps they were practising.
 
Anyway the same, or another, pair have returned and appear to be taking it on. We hope so.  We have been watching two of them flying around and occasionally alighting. Whether they are doing any more than staking a claim at this point we don’t know.
 
A Martin’s nest is made up of around 1,000 beak-sized mud pellets, so obviously they are dependent on a suitable supply of mud nearby. Usually this is no problem at all round here, but at the moment everywhere is unusually dry. The few dribbles of rain we have had this afternoon are not going to make much difference either.

Martins often do return to a previous nest, but of course this could happen . . . !
  
Thank you for all the comments etc. on my bluebell blip yesterday. It is such a wonderful place and we had a very special day, so it was great to be able to share it.