Why do bird congregate in large flocks?

Question from Doug: Every day at sun down, 100s of black birds congregate and the utility lines at Kirkwood and Westheimer. My questions are, what kind of birds are they, where are they during the day, and where do they spend the night?

Good question. People have advanced several theories as an answer, although no one knows the answer for certain. At any rate, the blackbirds congregating on power lines are usually a mixed flock of European Starlings, Red-winged Blackbirds, and Great-tailed Grackles. During the day, they forage over a large area that may include farm fields, marshes, grasslands, suburban yards, and city streets, The reason they congregate and perch at night on power lines is due to complex social behavior that 1.) helps them keep warm by huddling together, 2.) helps them avoid predators because it's easier for a group to spot predators and protect each other than it is for a lone individual, 3.) helps them find food because members of the flock can lead other members to the best feeding locations, and 4.) helps them locate food around the utility wires because the wires are usually at lighted traffic intersections with waste food from humans scattered on the ground and with insects attracted to the street lights.

The social interaction of birds that includes flocking behavior is an ongoing topic in ornithological research, and I'm sure we will learn more about the reasons for social interaction as research continues.