Why do thousands of birds congregate every evening in the same location?

Question

During the spring, summer, and fall thousands of birds congregate around our mall during the evening hours ( Lewisville, Texas), in the tress, on the phone line etc. Why do the do this, what are theying doing?

Answer 1

"WHY BIRDS ROOST
Communal roosting provides several advantages for birds. This phenomenon provides an opportunity for birds to find mates and to sharpen communication skills they use throughout the year. Some birds, because of their age or familiarity with the surrounding landscape, may be more efficient at finding food. Less experienced members of a roost can follow other birds to known feeding sites. Roosting flocks also provide a form of protection from predators. Birds occupying the center of the flock are less exposed to predators than those on the edges.
Several bird species roost in groups of hundreds or thousands. These roosting flocks may be composed of a single species or of several species. Birds that commonly roost in large numbers include starlings, house sparrows, crows, grackles, gulls, purple martins, red-winged blackbirds, pigeons, vultures and wading birds.


TYPES OF ROOSTS
Birds roost in a variety of natural areas and man-made structures. Natural roosting sites can include trees in urban parks and residential areas, haystacks, ivy, hedgerows, and marshy areas. Man-made structures chosen for roosting often include barns, ledges, chimneys, attics, flat roofs, airport hangers and runways."
http://edis.ifas.ufl.edu/UW087

Answer 2

I don't have an answer for you, but I notice the same thing here in GA, south of Atlanta. There are thousands of black birds that fly around and landing on wires, trees, just going back and forth for a few months. I remember they were here last year too. Maybe they flew south for the winter.