Swallow Wall

Generally the swallows and housemartins congregate  on the telephone wires but today the housemartins particularly kept flying off and clinging to the rendered wall of the old school. They didn't seem to be doing anything else - not eating spiders or chipping off grit, just clinging on and flying off.
I couldn't find anything about such behaviour but discovered a jocund visual pun instead. As a figure in heraldry the marten is depicted as having no feet, and is used on the coat of arms of a fourth born son. Thus, the bird not being able to land describes the land-less state of the younger son. Ho ho!