Crows and Herons

Yesterday evening, looking out of the train window as I travelled home, I saw a sight I'd never seen before. Two herons were perched high up in a tree among a couple of dozen crows who were taking up positions to roost - and who seemed quite unperturbed by the presence of herons among them. Whenever in the past I've seen crows and herons in any kind of  proximity, the former have been relentlessly mobbing the latter and driving them away. Are the crows changing their ways - and if so, why? There must be something in it for them, as they're extremely smart birds who in the past few decades have developed from solitary country dwellers to gregarious, streetwise urban scavengers. Now they are so numerous wherever there's a bit of water, herons too have changed their ways, becoming almost fearless in the presence of humans (now we're not shooting at them) and taking their place among the lesser waterfowl, even competing with the ducks for thrown bread.  But if a new age of detente with the crows is dawning, we may be sure it's the crows who are controlling the situation. I wonder what is going on. Has anyone else noticed this new behaviour, or was it an aberration?