House Sparrows - Passer domesticus - are known for communal nesting, these three are part of the colony inhabiting an old corn crib in the backyard. Also known as English Sparrows, they were introduced into Brooklyn in the late 1800s to reduce insect damage to crops. This must have been a government program because it turns out they are primarily vegetarian and not very useful for insect control. They have, however, proven to be very effective at displacing native bird species over a wide swath of North America.