If you have never seen this in person, it is truly something to behold. Every evening at dusk, but more notably during certain periods of the year, all the crows in Vancouver migrate out to the southeast. To call them a murder of crows would be an understatement as it is quite literally every crow that can be found in the city: it is the crows. It takes maybe 15 minutes for them to all pass overhead, sometimes swooping to the level of my sixth story apartment, cawing dramatically as they pass. I've never known why they go (or exactly where they go) nor when and how do they get back, but by the first light the next morning they are already covering the sidewalks, cleaning up the garbage left behind the night before.
The crows have been giving us a really great show the last few nights; I'd forgotten how I missed seeing them all summer long.