About the hanging hummingbird: Nancy Newfield, who lives in Louisana, is expert on hummingbirds. I wrote to ask her about this behavior (previous blog post). I asked the same question three years ago, too, that answer filed somewhere. Here is her answer, same as 2012:
I don't see any real 'behavior' here. These Ruby-throated Hummingbirds appear to be youngsters [both the original one and the current one, therefore not a returnee] and many recent fledglings embark upon the rigorous migration before developing their full strength. During migration, a certain percentage of them will seriously deplete their energy reserves [fat] and become weakened, at least temporarily. The only reason they do not fall to the ground or underlying substrate is that their feet automatically lock onto the perch, which may be a little slippery.
This is not a deliberate behavior; it just happens to an individual that is not ready for the task of an arduous migration. If I am not mistaken, most birds of most avian families will attack sick-looking individuals; perhaps nature's way of eliminating the infirm and less fit. Hummingbird attacks are generally not injurious though I know of a very few in which death occurred. Just because the attacker seems to be 'stabbing' the hapless individual with its bill, it seems unlikely that skin and flesh were actually punctured. Note that in the images from three years ago, there were at least two, and possibly three attackers, all appeared to be male [one adult and one or two immature males]. That is just the nature of the beasts.
Even in cases where 'the bird' left and 'returned later in the day', we cannot know if it was indeed the same individual. During the course of migration, especially southward migration, the toll of casualties is quite high. These energy-deficient youngsters are the most vulnerable. They are less able to force their way to a feeder and are much more vulnerable to predators.
I cannot think of any other reason this 'behavior' is occurring. Therefore, the only thing I can add is that they might not be migrants this early in August. As of last Saturday, 1 August, I have noted a very few at my place [where there is no breeding population] and action is not 'red hot' at a banding site north of Lake Pontchartrain as it will be toward the end of August through the third week of September. Currently, we are handling adults in heavy molt, which is typical for post-breeding adults. None has much fat.
Many thanks, Nancy.