Karen

Here in Vanvouver British Columbia the crows choose one of the busiest intersections in this urban area to congregate on winter evenings.  As the rushhour traffic streams below them, thousands of crows stream from every direction to occupy tree branches, telephone wires and roofs.  I wonder what impels them to travel so far to congregate with others of their kind?  Does each bird have its own designated perching site?  Who decides who sits where?  Do they have to purchase tickets?