There is a huge sycamore tree close to my apartment which is on the sixth floor. Early one morning in December, 2017, it was still somewhat dark, I pulled back my curtains and the tree was full of crows! Hundreds! They all seemed to be facing north. And if that wasn't enough, a full moon was behind the tree, one of the most beautiful things I have ever seen.
I think the crows selected this spot mainly because of warmth, the tree is located at the corner of a section of the building. There is a creek nearby so easy access to water. Food, other than what people drop on the sidewalks I can't think of any sources in the immediate area.
Location, 200 block of Geneva St. Ithaca, NY
To help slow the spread of West Nile Virus, eliminate mosquito breeding habitats; containers left outside neglected that collect water. I don't own a pond but I think there are things that can be added to the water to discourage mosquito breeding, don't know how safe these things are. Also creating a dragonfly habitat, dragonflies eat mosquitoes like I go through popcorn!