Tree Swallows gather in large flocks before migrating south to sites in the southern United States, Mexico, the Caribbean, and Central America. Along the New England coast, they can often be seen eating the waxy fruit of Bayberry (Myrica pensylvanica).
It's hard to show the scale of these Tree Swallow flocks — many hundreds of birds swirling overhead. At one point, with their white bellies glowing against the blue October sky, they looked like a blizzard of white snowflakes!
Who wants to count the number of birds in the last photo (above)? :)