The hypothisis I've heard is a female testing out the male to see how agressive he can be with intruders on his territory. Males will challenge any hummers on their territory male or female. The females wait to be impressed. An example of sexual selection of agression in this bird (they're not just little sociopaths :-).

See on page 215 and 216 of this paper for a very similar description of contact and "knock down" behavior between males and females. I've not seen this though I've seen other behaviors leading up that point and the "shuttle display".

http://elibrary.unm.edu/sora/Condor/files/issues/v084n02/p0208-p0225.pdf

On Feb 5, 2011, at 2:36 PM, Mary Metz wrote:

> Yesterday peregrines, today I want help understanding Anna?s hummingbird behavior.
>
> This morning I saw a pair of Anna?s hummingbirds either battling or mating. My attention was first caught by something small plummeting from about ten feet in the air to the ground. At that point they were hidden behind a boxwood and I?m not sure what happened but they were out of sight for only a few seconds. This was followed by about two minutes of the two birds, one male and one female, face to face in flight, seemingly banging their beaks and knocking their wings against each other as they rose and fell? So it seemed like fighting but he was also spreading his tail and flashing his colors; what was it? A female tired of very aggressive courting?
>
> -Mary
> maryjmetzatyahoodotcom
>
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