Progress on the orange-throated hummingbird mystery

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Thanks to Sheri Williamson (author of the Peterson Field Guide to Hummingbirds) and her recent post titled Orange-throated hummingbirds – not so mysterious after all, we have a solid contribution towards understanding the orange throats of some Ruby-throated Hummingbirds, although I contend that mysteries still remain.

There is still no full explanation for the color difference shown by these summer and winter hummingbirds. Adult male Ruby-throated Hummingbirds - three in breeding plumage (left) collected in April in Florida, and three in nonbreeding plumage (right) collected in Oct-Nov in Mexico. Specimen use granted by Museum of Comparative Zoology, Harvard University ©President and Fellows of Harvard College.

She explains the details of iridescent color on hummingbirds, and a plausible mechanism for color shifts with wear. She also includes two photos that seem to show pretty conclusively a color shift on worn feathers. Given this I stand corrected and I retract the suggestion in my previous post that color shifts with wear are unlikely. Apparently they do occur, and I am glad that Sheri has taken the time to explain it.

That still doesn’t solve all of the mysteries, although it does point to some interesting possibilities for answers.

Since wear is part of the equation, it’s likely that all Ruby-throated Hummingbirds become slightly more orange-throated over the course of the summer (and there must be some individual variation in the amount of orange shift). And since throat color is mainly being judged subjectively by birders and banders comparing one bird to any adjacent birds, a slight orange shift in all birds would not be noticed, and the throat would have to get really orange before it stands out from its peers.

Wear alone could explain the very drab orange throat color shown by all of the winter specimens at MCZ (see my first post on this subject), but only if there is no late summer molt. In other words, if throat feathers were molted only once in late winter they would be fresh in spring, becoming slightly more orange by late summer and very orange by midwinter. But the late summer molt is well-documented by Dittmann and Cardiff and is confirmed by hummingbird banders.

Donna Dittmann, Cathie Hutcheson, and Scott Weidensaul have all told me that they see no difference in throat color in late summer between the old feathers being dropped and the new feathers coming in. Although Sheri Williamson has posted a photo showing a Ruby-throated Hummingbird acquiring new feathers that are more red than the old ones. I wonder which is the norm? Do the incoming feathers usually look a little more red than the old ones, or do they look the same color?

If new feathers look the same color that would imply that the new feathers being acquired in the late summer are not as red as the feathers that were acquired in late winter. In that case the continued effects of wear during winter could lead to even drabber orange feathers by mid-winter. If the feathers acquired in late summer were also somehow weaker and more susceptible to wear that would lead to even more wear and even drabber feathers.

Interestingly, this hypothesis actually comes back around to my original idea, that the orange-throated specimens at MCZ are in a drab, “nonbreeding” plumage, one that becomes drabber and more obvious as the winter progresses. Contrary to my original post (and as corrected in my second post) the orange-throated males seen in late summer are not the same as the orange-throated winter specimens. Birds in worn summer plumage sometimes become obviously orange, and based on the MCZ specimens birds in worn winter plumage are always orange.

25 thoughts on “Progress on the orange-throated hummingbird mystery”

  1. David,

    Thanks for sharing your evolving theories on this. It is interesting seeing the thought process for something like this as more people chime in. I helped band RTHU in central Pennsylvania over the weekend and kept an eye out for any orange-throated males. We caught about 15 and my impression was that they were less red than they are in spring. None were really orange, but most that I looked at in good light seemed to have a range of orange tones in with the red.

    1. Hi Drew, It’s been a fascinating study, if a bit humbling at times as I have to keep retracting or revising my previous speculations. I’m glad you’re enjoying watching the process, and excited that we might be getting closer to really figuring it all out.

  2. Here in the area around San Antonio, TX in central Texas in previous years I have seen orange-throated ruby-throated hummingbirds at my feeder and have photos of orange-throated birds at a local nature center during the August migration peroid. I came across this discussion while viewing a orange-throated bird posted on August 15, last week, on flickr by another birder in my area of San Antonio. Someone posted a comment that the bird looked like the birds being discussed here.

    I wonder how many others in Texas have seen the orange-throated birds.

    David, thanks for looking into this mystery!!

    1. Lee, I live in Kerrville, northwest of San Antonio and have observed the same species here over the past few weeks!

      1. I live in the Shenandoah Valley, Virginia, and my room mate said he saw a small hummingbird this morning with a gold throat. He thought it was a baby. I don’t think this would be a molt issue. The weather is cloudy and raining as well. Strange.

  3. I live close to Fort Worth Texas and have never until this year had the pleasure of seeing this neon orange-throated bird.
    The answers for this have been fading of the red, but I find this hard to believe since it is so bright.
    Whatever the reasons are I am happy to have them.

    1. Tanna, iridescent colors don’t fade like pigment-based colors do. What’s happening is a change in the refractive index of the feather structures that changes the wavelengths of light emitted from the feather. Exactly how the aging process causes that change is still unknown, but a grad student who’s studying feather iridescence has offered to help us figure it out. Stay tuned!

      1. Hi Sheri, I’ve just put up a new post about how these iridescent colors are created. The basics of iridescence in hummingbirds
        A change in refractive index is one thing that could slightly alter the reflected color, but there are many other factors that could lead to similar changes in color. We just don’t know yet what causes the orange throats of some Ruby-throated Hummingbirds, and there may be more than one cause.

  4. I had an orange throated male in my garden all day today, a bronzey copper colour in very strong sunlight, much more orange in bright shade.
    three photos on my blog, taken a different times of the day

    1. Thanks for your comment Joann. Your web link doesn’t show up to the public so I’m adding it here.
      http://jmcda.blogspot.com/2011/08/orange-throated-ruby-throated.html
      This looks like a great example of an orange-throated bird. Presumably it’s a male that hasn’t started molting yet and has worn throat feathers, but many birds have finished molt by this date so it’s possible that it is in an orange “non-breeding” plumage. If it stayed around it would be very interesting to see more photos from a week or two later.

  5. Two year in a row (’09 & ’10) I had a knock-your-socks-off orange throated ruby throat at my Cardinalflowers in mid-August in southeastern Pa. The throat was brillant orange (not even close to the typical ruby color) and (at least superficially) uniform. Based on the rarity of these sightings, it strongly suggests that it was the same individual, which might indicate a genetic basis for the orange throat. This is not to say that it is not associated with wear, since there could be a genetic origin of a unique wear sequence. I also find it fascinating that most records of brillant birds appear to be in August and duller birds in late fall and winter. Could these birds have a genetic link between an early molt (pre-August) and the orange color that wears to the duller, mottled winter birds? And does the orange color ever occur in spring and the breeding season? Maybe there is a small birderless area in southern Canada – maybe north of Lake Huron – where an early molting, orange-throated gene results in a few individuals that might migrate southeast to eastern Pa. or southwest to Texas and Mexico. Why don’t we see them in the spring migration? Maybe they don’t stick around long enough.
    David, great job. Keep it up.

  6. Bruce in Vermont

    I just saw an orange throated humming bird yesterday, 8/7/12, in Island Pond, VT, which is in the northeast corner of Vermont, about 20 miles from Canada. It was a very bright orange.

  7. I just saw an orange throated hummingbird that just blows my mind here in central Missouri (9/9/12). Aside from the orange throat it looked like the Ruby Throated. The color was so brilliant and flashed like diamonds. Have never seen anything like it.

  8. I have 7 hummingbird feeders out from early spring until October. Needless to say, we have seen many hummers in the years we have lived in Palestine, Texas. Last week, we had an orange throated hummingbird at the feeders for one day. We are amazed, as we have never seen one and didn’t know what to think about this. I found your website and have now been enlightened. I will keep checking back for updates.

  9. Mary Sullivan

    I was curious of your mentioning of the orange-throated variety of the Ruby. I started photographing my hummingbirds last summer and fall and noticed that one of mine had a green throat, I’ve got an excellent photo of it. Have you had any more reports? We had a terrible drought last summer. Perhaps malnutrition?

    1. Hi Mary, A Ruby-throated Hummingbird with a green throat is a much rarer anomaly! There are a couple of records that I am aware of – one from Alabama with photos here http://www.pbase.com/fdietrich/green, and one from Louisiana with photos here http://www.flickr.com/photos/8246174@N02/

      If you could send me your photo, or a link to it, it would be great to see. The throat color is probably not related to the drought, although poor health of the bird can lead to drabber throat feathers, the photos linked above are full and bright colored birds that have grown the feathers a little “off” so they reflect bright green rather than red. It’s a difference of a few nanometers in the thickness of air bubbles in the surface of the feather, and what’s amazing is that this kind of anomaly doesn’t happen more often.

  10. I always assumed the orange was just the angle of the light & bird, but while researching Ruby-throated Hummingbirds in molt I came across this very interesting string of articles. Thanks so much!

  11. Newton Wallen

    I know this thread is a little old, but hope this helps. I photographed one yesterday (3/31/2015) that had a gold throat that tapered to ruby along the edges. I live in NE Florida.

  12. We live in northwestern CT, and yesterday, May 16, I observed that one of our hummingbirds has an orange/gold throat. We only confirmed the presence of the first males of the season here on May 9. We did see and orange-throated one last year as well, though I do not recall seeing him/that plummage early in the season.

  13. We have a orange throated hummingbird this year.this is the frist time.live up by Haward wi. Do they live this far north.

  14. We are located in Northwest Arkansas and have been watching a very territorial hummingbird. He (?) only has one dot of iridescent plumage (smaller than a pencil eraser) right on his (?) throat. He sits on top of the shepherd’s crook that holds the feeder. He has been protecting his “domain” all morning. The oddest thing is the “dot” is only visible in a certain position. It looks like he has a laser pointer directed at his throat with the pointer being orange in color! Is this a molting male?

  15. I live in the northeastern part of Georgia and for the first time, I have seen one of these beautiful creatures in my front yard. I was watching the hummingbirds at the feeders, and I noticed on some of them was a glowing feature in the throat of a gold color. I have never noticed this in years past. They are beautiful as all creatures are.

    1. I am in Southeast Missouri Every year for the last four years I have had an Orange Throated Hummingbird that stays in my yard from the start of summer to the end of summer . He is the first one to arrive every year and the last one to leave. His throat is defiantly bright orange. I have never seen it dull from molting, he seems to stay bright the hole time he is here. I have named him Tuby because he is very territorial and gets good and plump when he is here. Shortly after he arrives the same female shows up too. I named her Tubiet. She also stays here the hole duration of the summer with him. Other hummingbirds come and go, but he is here to stay every summer. He is beautiful.

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