White Hummingbird

These are the diagnostic interpretations of Susan Allerton, Durango Bird Club
Mystery hummingbird thoughts:
Yesterday, I had a chance to view the hummingbird coming to the
Pfeiffer's feeders. (The Pfeiffer's place is only about 3/4 mile
from where I live.) In addition, I carefully studied the excellent
photos that Marsha Pfeiffer and Robert Winslow took. After
consulting several references, I concluded that the bird is either a
Black-chinned Hummingbird or a Ruby-throated Hummingbird because the
inner primaries are much narrower than the outer primaries on those
two species. That seemed to hold true for the bird at the Pfeiffer's
house. That determination narrowed it down to one of those two
species, both in the genus Archilochus.
Tail differences and outer primary differences seem to be the
key field marks for separating Black-chinned Hummingbird from Ruby-
throated Hummingbird. On the Ruby-throated, the outer
primary "tapers to a narrow rounded tip". [The outer primary (p10)
is of a narrower width that the next primary (P9).] On Black-chinned
Hummingbirds, the 2 outer primaries are of similar width. The outer
primary on the Durango hummingbird seems to be a similar width to the
next primary. That would agree with an ID of Black-chinned
Hummingbird. As for the tail differences, the tail on the Black-
chinned Hummingbird is slightly shorter than the Ruby-throated
Hummingbird. The best way to distinguish the tails of the two
species would be to observe the closed tail from the back. If the
graduated lengths of the tail tips are visible, you'd be able to
count 3 or 4 tail tips on the folded tail. 3 tail tips would
indicate Black-chinned; 4 tail tips would indicate a Ruby-throated.
I believe that the 2 outer tail feathers would not visible on the
folded tail. If true, 3 tails tips would be visible, indicating
Black-chinned. All of the above information was gathered from the
following sources: Sheri Williamson's Hummingbirds of North America,
Hummingbirds of North America by Steve Howell, and Identification
Guide to North American Birds by Peter Pyle. The last reference
indicated that the shape of the 6th primary is another significant
way of separating the two. That primary feather is slightly less
attenuate & more rounded on a Black-chinned Hummingbird than a Ruby-
throated. The 6th primary shape (visible on a couple of the photos)
seems correct for Black-chinned Hummingbird. Consequently, all the
field marks seem to be pointing to Black-chinned Hummingbird for me.
However, I'd really be interested in hearing what the hummingbird
experts think.
Many thanks to Marsha and Bob Pfeiffer for reporting this
interesting bird. I also appreciate receiving all those excellent
photos from Marsha Pfeiffer and Robert Winslow. All the finer
details of the bird are much easier to study in the photographs!
Susan