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Not sure
According to Wikipedia, adult Scintillant Hummingbird in its entire range has a brilliant red throat separated from the cinnamon underparts by a white neck band. Volcano Hummingbird in the Talamanca range, has a grey-purple throat, the rest of the underparts being white. By throat description, this bird would be a Volcano Hummingbird but the underparts point to a Scintillant Hummingbird.

Changed Taxon
Media was moved from ID Request. Ted's comment made me have another look at the Stiles/Skutch book. Plate 25 #3a states that the Talamanca males have a "purplish-gray or purplish green" gorget. The Scintillants are orange-red. So I think it's OK to move it.

Wait
Sorry Mike, the more I check the more confused I am so I edited my comments as you were entering yours. I need to do more research.

Details
I'm now rereading the full species descriptions, so I'll see if I can learn anything new.

Volcano Hummingbird
I found a great image of Volcano Hummingbird on Fickr, the comparison is very good. If that image was taken just a bit more downwards and more from the rear the white underparts would not be as visible. I believe that if the photo here was taken more from the front and more from under side then underparts would show a lot more white. I hope this makes sense.