TOWARDS DUSK at this time of year, starlings congregate in vast flocks as they prepare to roost. Small parties travel up to 20 miles to join up in assemblies. Then, for maybe half an hour, they perform violent aerobatic manoeuvres, the whole mass of birds whirling, diving and climbing in unison, to the accompaniment of continuous screeching. Finally they cascade like black hailstorms on to whatever building, or into whatever thicket, they have chosen, and carry on arguing furiously about who has precedence on the most comfortable perches. Males rule the roost, but in really cold weather the birds huddle shoulder to shoulder for mutual warmth.
The motive for this massing seems to be that there is safety in numbers. Foxes, rats and badgers lurk below the roost, confident that some birds will drop off; but in a crowd of thousands, the chances of being eaten are small. More at risk than the starlings are the buildings, trees or bushes on which they descend, for the birds' ammoniac droppings are strong enough to dissolve stone and kill vegetation.
The birds are extremely persistent: attempts to drive them off have little effect, leaving many a municipal authority with a huge annual bill for cleaning.