David:

I would say behavior is most certainly density-influenced. In the South and mid-west (and even at Tom Lamb's in Liberty) migrating hummers seemingly "give up" territoriality and "swarm" feeders placed in close proximity. Anecdotal experimentation, once again in the South (west), has shown that if feeders are spaced further apart within the same area, "alpha" hummers will attempt to defend them. Of course, birds in migration have other factors influencing bahavior as well.

During the seven years we have been observing hummers in our yard, we have seen territories (formerly the entire yard defended by a single bird) shrink to the point now where they will regularly perch within 5 feet, but not visible to each other, both stretched out in the squeaky gate vocalization.

chuck reinsch, magnolia