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When Black is Green: Iridescence on Common Loons
In a recent post to Oregon's statewide birding listserv, veteran observer Wayne Hoffman shared that on two different days during the second week of April 2010, he had seen alternate-plumaged Common Loons (Gavia immer) at Newport, Lincoln County, Oregon that showed green iridescence on their lower neck collars. This observer went on to note that he had not ever seen a Common Loon showing bright green on the lower neck collar. His subsequent search of field guides and other references found very little mention of green iridescence in connection with this species.
Wayne's post reminded me of a similarly plumaged loon that I photographed at the same location in April 2009. The alternate-plumaged bird that I observed (see images below) showed the same green sheen he was describing on both its head and on its lower neck collar, with the lower collar being particularly colorful. I can remember being a bit taken aback by how green it looked at the time and how I was completely unaware that a Common Loon might show such coloration. Then it occurred to me that I'd never before been so close to an alternate-plumaged loon in crisp sunlight.
In just the right light, the green iridescence on an alternate-plumaged Common Loon can be quite striking, as was the case with this bird photographed at Newport, Lincoln County, Oregon on 26 April 2009. (Photo by Dave Irons)
A quick check of the most popular North American field guides revealed that nearly all of them illustrate alternate-plumaged Common Loons with a black head and black lower neck collar that are separated by an incomplete upper collar that is mostly white with narrow, dark vertical lines. The accompanying text in these volumes generally describe the head as black, which is how we perceive it in most light conditions.
Here's another shot of the same bird at Newport, Oregon on 26 April 2009. (Photo by Dave Irons)
Of the guides that I own, the 4th edition of National Geographic's Field Guide to the Birds of North America seems to best depict this green-headed appearance, but offers no description of the summer plumage in the text. The next best illustration that I found was in my 3rd edition of Peterson's Western Guide (1990). I don't own the most recent editions in the Peterson series, but I was a little surprised to see that the Common Loon in the 5th edition of Peterson's Eastern Guide (2002) showed a more purplish-blue gloss to the head and none of the green tones that are apparent in the earlier Western Guide. Maybe this was just a matter of printing, or perhaps the result of an editorial decision to show this species as we most often see it. In the Sibley Guides, which to my eye offer the best overall set of illustrations, alternate-plumaged Common Loons are shown to have black heads, which is pointed out with arrows and labeling. Perhaps, like others, Sibley made the editorial choice to show his Common Loons with black heads because that is how they appear to us most of the time.
After reading this piece, USFWS biologist Roy Lowe passed along this photo of a Common Loon that he saw on Yaquina Bay at Newport, Lincoln County, Oregon on 10 April, 2010, the day of Wayne Hoffman's original observation. It shows the green iridescence on the head and neck collar more clearly than the two photos above. (Photo by Roy Lowe).
One point that is important to remember, iridescent colors are not produced by feather pigmentation. Instead, the glossy blue, green, and purple hues that we perceive are the result of light refracting off of the intricate structural characteristics of the feather. That being the case, whether we actually see these colors and how intense they appear is highly dependent on lighting conditions. Generally speaking, the brighter the sunlight, the brighter the apparent coloration.
At the very least, we hope this discussion inspires you to take a closer look the next time you see an alternate-plumaged Common Loon and to better understand how lighting affects the colors our brains are telling us we are seeing.
Thank you so much for your explanation of colors on feathers. We are doing our Spring Nature Study – Spring Birds today and this answered our exact question. :)
Thanks for following up on this. One point I tried to make in my OBOL post is that the iridescence probably varies a lot within the population. I doubt that palmer’s description of purple on the lower neck was wrong, just a different bird. Common Loons vary a lot in size geographically, but in a cline. If I remember correctly, the ones in the south-center of the breeding range (i.e. Minnesota and adjacent Canada) are smallest, and they get bigger to east, west, and north. Most winter on the coasts, and likely Atlantic winterers and Pacific winterers overlap in breeding distribution. I wonder if differences in iridescence are geographic or just individual. A question for people lucky enough to study them in breeding lakes.
Wayne
Thanks for this Blog!
Tonight I looked at the Common Loon account in The Birds of No. America Online (see citation below). It discusses that not all
aspects of age-related molting to Definitive Alternate Plumage
(breeding plumage) are known, especially for 2-4 year old loons.
Below is an excerpt relating to head and neck color in the Appearance, Molts and Plumage section for adult Common Loons; note that they suggest that even the “upperparts” can have a slight green or greenish blue sheen:
Definitive Alternate Plumage
…
Sexes alike. Head and neck velvety black; chin, throat, foreneck, and
part of side of neck glossed with green; and hindneck glossed with
purple; sharp line of demarcation between black neck and white breast;
a transverse line of small, white spots (6–12) laterally, and very
short vertical stripes medially high on foreneck below head; an oblong
patch of vertical, parallel, white stripes (these sometimes forked and
may change with head and neck movements), on each side of neck; each patch widens toward rear, tapering front and back, patches not quite joining in front or back on either side of neck. Upperparts black with slight green to green blue sheen. …
Recommended Citation
Mcintyre, Judith W. and Jack F. Barr. 1997. Common Loon (Gavia immer), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/313
hi,
am looking for help. driving home this evening, found a bird (waterfowl)on the side of the road. it was sitting on it’s chest and could not get up on its legs. it is zero degrees here and the chances of anyone else coming by and finding him were nil. we picked him up and wrapped him in a towel and brought him back to town to odfw. no one there. thanksgiving holiday. phone message we got recommended we go to sheriff office. we went and were informed that they didnt want it. told us odfw would just knock it in the head. like i said, no one was at odfw, so we brought it home and put it in a large box. we guess it is a female loon. loons are described as having red eyes, but this one has black eyes. a cursory exam led us to believe that one of her legs doesnt work. she is fairly plucky. is still defending herself and is sitting up on her chest. we don’t know what to feed her and would like to see if we could rehab her. any suggestions? help. thanks.
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