These are Cedar Waxwings. The "Cedar" part of the name comes from their fondness for seeds from the cones of Eastern Red Cedar (which is really a Juniper, not a Cedar.) The "Waxwing" part comes from the red wax that is secreted along the shafts of the secondary wing feathers. Like other colorful birds, this red wax seems to play a role in attracting a mate.
They are known for their very social nature, and they are rarely seen alone. They are very polite to each other, taking turns and feeding in shifts when food is limited. They also tend to get intoxicated frequently, from eating fermented berries.