if it's going for the bottom part of the window i'd guess it's territorial and he's seeing his reflection against the dark of the plant pots. it could be going for the plants, but unlikely, unless they are trees! you could try putting patterned paper or something on the pots to break up the reflection. white paper might do it too.
Crackle... it's one of the main rules of photography. the other week i didn't have my 500mm lens... great views of a woodpecker in the open, but too far away. one day i didn't unpack my camera... water vole on a bank, look up and see a woodpecker on top of a tree quite close by, into a hide and a water rail swan right past and even looked through the window at me. it's the law. mind you, herons common as muck round these parts - chick killing lumbering creatures that they are.
fnaar... i saw sand martins yesterday. i spotted at least two, there were reports of ten. they're on their way. wrens are pretty noisy themselves... sometimes birds know it's safer to build near working humans - look at the amount of cases of unusual nest locations that come up. it means there less likelihood of predators such as hawks, foxes, etc.
GC Grebelets!!!!! where, let me see them!!!! Swans do like showing off their babes, just don't get too close (unless the swan is your friend).
