Pigeons clinging to walls

[Khandro]

I have just returned from the canals of Burgundy, and one sunny morning saw on a long 5-arched stone bridge which crossed the canal and the River Yonne alongside it, a large flock of pigeons trying with mixed success to cling to the vertical stonework. They would grip the stone with their feet flapping their wings until they could get a satisfactory hold, then (those who succeeded) would remain still with wings outstretched and the side of their head against the stone. I first thought it was something to do with insects for food, but they didn't peck at all. Anyone any idea what they were doing, could it be playing, simply showing off that they could do it?