That is amazing - it is like a communal construction effort - five pairs all chipping in to enlarge and line a hollow suitable for nesting - If only humans could be so collectively minded we might solve our housing crisis
Isn't it interesting? I'll post another sighting now, just to show interest in the hollow - I think it's not just pairs of gang-gangs that visit and chip away. And yes, how much could we, as humans, take away from our feathered counterparts?