I was intrigued to see yellow pollen arriving at the hive doors and a short walk gave the answer. Some 500 yds away round the tree line were some 20+ willow trees, some in pollen and others going over and yet others about to open up so a first class source. I have included a picture of my home made mouse excludeers which guard the nucleus hives from vermin. Cheap and cheerful made from 9mm marine ply they work well. If I get two or three years out of them then they are well worth the small effort to make them.