According to Russell,S.M. 1996. Anna's Hummingbird (_Calypte anna_)
_In_ The Birds of North America, No. 226 (A.Poole and F. Gill eds.)
The Academy of Natural Sciences, Philadelphia, and the AOU,
Washington, DC.

"Onset of winter rains starts nesting. In California chaparral,
male moves into breeding territories... in Nov or Dec."

and

"... very early and very nestings may reflect a shift in the breeding
seasons in the peripheral, newly occupied portions of the range
where exotic flowering plants largely replace native species."

Nesting in Oregon has been documented in January and February as far
north as Newberg (south of Portland).

Eugene Hunn wrote:
>
> Tweets,
>
> I've got two male Anna's hanging around my feeders and just now the one with
> the full gorget was perched above the feeders singing while the other male,
> with a still partial gorget was engaged in his full display flight, towering
> up about 30 feet then careening straight down, the wings making a loud
> "cheep" at the bottom. What's going on? The singing male seemed to ignore
> the display. Also, is there any evidence that Anna's might breed twice in a
> year? Once in late fall-early winter, then again in early spring? In any
> case, they seem to sing most of the year (with a notable absence or scarcity
> in late spring-summer.
>
> Gene.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

A child who becomes acquainted with the birds about him
hears every sound and puzzles out its meaning with a cleverness
that amazes those with ears who hear not.

-Neltje Blanchan

http://www.pacifier.com/~mpatters/bird/bird.html