To what extent do hummingbird hybridize?

I spent yesterday afternoon taking a break from grading final in the
company of a handful of other birders looking at a hummingbird that fell
into the "none-of-the-above" category.

The owner of the feeder it is visiting thinks that it is a Costa's; some
previous observers have thought that it was an Anna's. The weather
(rain and clouds and thus very flat light) have not helped. Yesterday
there was patchy sun. The bird came into the feeder about every ten
minutes for the two hours we watched; it stayed 1+ minute per visit. Also
feeding were Calliopes, Black-chinned, and Rufous hummingbirds. The
feeding frenzy made the birds very tame and we could approach with a
foot of the feeders.

The bird:

DESCRIPTION:
SIZE: a large bird, the size of the Black-chinned and Rufous; it was
distinctly larger than the Calliope. For example, when the Calliope sat
on the feeder, they had to stretch their necks to reach the holes; neither
the mystery bird nor the Black-chinned or Rufous were required to do so.

HEAD: the gorget and cap were a deep purple; the flanges of the gorget
extended back beyond the shoulders and were somewhat flared away
from the body. The space between the gorget flanges and the cap was
triangular and indistinctly grayish white. There was also a small
triangular white patch immediately behind the eye.

BODY: the back, tail, and wings were green. The breast beneath the
gorget was white. A whitish strip ran down the middle of the belly to the
undertail coverts separated two greenish areas, one under each wing.

TAIL/WINGS: the wings were no longer than the tail. The tail appeared
to be rounded.

ACTIONS: when the bird came into the feeder, it would sit on the perch
and feed. It did not flick its tail as Costa's are reported to do. It
was silent.

DISCUSSION:
SIZE: the size of the bird was what was immediately troubling about the
possible identification as a Costa's since a Costa's should be about the
size of the Calliope and distinctly smaller than either the Black-chinned
or Rufous. The Calliope is the smallest and the Costa's the second
smallest hummingbird found in the U.S.

HEAD: the coloration of the gorget and cap eliminated the Anna's which
is a rose color. The purple of the mystery bird's gorget, however, was
deeper and richer than any of the photographs of a Costa's gorget. The
triangular patch formed by the gorget, cap, and back/shoulder was much
less well-defined and much greyer than the photographs of Costa's.

BODY: the breast/belly area was very different than the grayish, mottled
coloration of an Anna's; it was similar to the Costa's and Black-chinned.

TAIL/WINGS: on the Costa's the wings extend beyond the tail. On the
mystery bird, the wings were no longer than -- and perhaps shorter than --
the tail when resting.

My personal conclusion was that the bird was a Costa's x Black-chinned -
- hence the question at the beginning of the post.

The bird is at a private residence and the homeowner has requested that
the address not be posted.

dale goble
moscow