Patrick van der Sande has added a photo to the pool:
House Martins, Delichon urbicum / Huiszwaluwen, have their way of saying Thank You for letting us live above your winegrapes.
I miss them when they go south and it is a joy when they return in spring.
Source : https://www.flickr.com/photos/patrickvandersande/55488012622/in/pool-912056@N21
