Bird of the Month: Which hummingbird did we spot?
|
I received the following comment in response to my February entry on hummingbirds:
Daniel Kreeger and Mom on May. 24th, 2009 at 7:31 AM: I thought it would be worth sharing my response with all readers of this column. |
|
‘Dear Daniel Kreeger and Mom!
You are a very observant pair! I do not know for certain what species of hummingbird you saw. However, I can make a good guess. First, though, I’d like to offer some background. The colors of hummingbirds are special. Much of their plumage is iridescent, meaning that as the angle of light hitting it changes, the color we see changes. This is unlike the non-iridescent reds and yellows and the blacks and browns we often see on birds such as finches and sparrows, which are caused by deposition of various kinds of pigments in the feathers. Iridescent colors, by contrast, result from the structure of the feathers. (Refraction and reflection of light off these feathers cause interference between different wavelengths of light, and thus, at different angles, only particular wavelengths of light are visible). While iridescent coloration can be very showy—and male hummingbirds make the most of their iridescent coloration in displaying to females—the angle of the light must be right for us to see the color. At some angles, iridescent feathers will appear to us black. |
|
A good example of this is the picture on the right of the head of a a male Anna’s Hummingbird. The entire cap and throat (or “gorget”) should appear to us pink, but notice how much of the head appears blackish-brown—the result of seeing it ‘at the wrong angle.’
I flipped through some field guides to hummingbirds to see if there are any black hummingbirds. There are over 300 species of hummingbirds! Most of them are restricted in range to South America, Central America and Mexico. Only a small number occur in the United States, and just a handful in the Bay Area. |
 male Anna’s Hummingbird (Calypte anna) Photo credit: Len Blumin, Mill Valley, CA |
|
There are a few hummingbirds that have extensive black coloration (or, at least, what appears to human beings to be black—because birds can sometimes see wavelengths of light that we cannot). However, none of the hummingbirds that occur in the U.S. are black. So, I find it unlikely that you saw a black hummingbird. More likely, you were lucky enough to observe one of the effects of iridescent structural coloration—you took the time to look, and you noticed that a bird that should be resplendent can appear black—pretty cool!
Now, which hummingbird did you see? |
 male Anna’s Hummingbird Photo credit: “randomtruth”  male Calliope Hummingbird Photo credit: “prayingmother”  male Black-chinned Hummingbird Photo credit: Marj Kibby, Newcastle, Australia |
The most typical hummingbird in the Bay Area—and the only one we can see year-round—is Anna’s Hummingbird (Calypte anna). Also nesting here is Allen’s Hummingbird (Selasphorus sasin), and a common migrant is the closely related (and very similar-looking) Rufus Hummingbird (Selasphorus rufus). Occasionally, we see other species of hummingbirds here. Though I have never seen it myself, the Calliope Hummingbird (Stellula calliope) occurs as a migrant in the spring, typically in inland chaparral. Going further inland—to the Sacramento delta—another species that can be found in the spring and summer is the Black-chinned Hummingbird (Archilochus alexandri). One winter, a vagrant Costa’s Hummingbird (Calypte costae) graced my neighborhood in Berkeley; and I’m sure there are many more instances of locally rare or vagrant hummingbirds that I’ve either forgotten, or haven’t heard of.
|
 male Allen’s Hummingbird Photo credit: “sgrace”  male Rufous Hummingbird Photo credit: “ianredan”  male Costa’s Hummingbird Photo credit: Christopher Fritz, San Diego, CA |
|
However, the only locally common species with a completely red head is Anna’s Hummingbird, and that is the species I think you saw.
Thank you for sharing your story. Good observation skills! Let me know if you come up with a different conclusion as to what you saw!’ |
Incidentally, blue feather coloration is also generally a structural color. In this case, the structure of the feather tissue absorbs most wavelengths of light, but scatters the shortest (blue) wavelengths. That means that we will only see the color when the light rays that reach our eyes are ones that have been reflected off the bird. Compare the two pictures of a Western Scrub-Jay below. In the one on the left, the sun is behind the bird, and we cannot see its blue color. In the other, the sun’s rays are reflecting off the bird, and the and we can see the blue in all its glory!
 Western Scrub-Jay (Aphelocoma californica) Photo credit: Sandy Harris, Central Coast, CA |
 Western Scrub-Jay (Aphelocoma californica) Photo credit: Debra Roby, Hercules, CA |
