Hi folks,
Several people responded with terrific observations about this bird. The consensus was that the photos are of a juvenile female Black-chinned Hummingbird.
Thank you very much to the esteemed birders who responded. I was humbled by the breadth of knowledge shown in responses!
Here are the reasons, summarized:
The dark stripe extending down from the eye over the ear coverts is a good mark, easy to see and different from the others. And the general lack of warm color below and no orange in the tail.
The six inner primaries, p6 and below, are much narrower than p7 through p10.
The buffy feather edges on each of the feathers in the crown, back and rump are a juvenile character. All NA hummingbirds will show this but it's most obvious in Black-chinned and Ruby-throated. It creates a dingy, scalloped effect visible in flight and at a distance. The buffy feather edges will wear off in older hatch year birds but we seldom see that in CO.
The fine striations or grooves running the length along the sides of the maxilla, or upper mandible. The grooves recede as the bird ages to its 2nd year when the bill will be largely smooth. Juvies are groovy, adults are smooth.
The very lightly spotted but relatively clear, or a fully clear throat and breast, and the very light buffy sides are typical female Black-chinned, BCHU. Female Broad-tailed, BTHU, will have rows of distinct spots pretty evenly distributed in the throat. Juvenile female BTHU will never have an iridescent throat spot, but ~29% of adult females will have one or more iridescent red spots. The iridescent feather count can go to 30 or more, causing some folks to confuse female Broad-tailed with female Rufous, RUHU. But of course, female Rufous don't breed in CO and are rarely seen in spring migration. Neither adult nor juvenile female BCHU ever show an iridescent throat feather. The sides of BCHU are more light buffy or dingy white in BCHU, whereas BTHU sides are more rufous.
Richard Trinkner
Boulder
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