Orange-throated hummingbirds: Not so mysterious after all

The gorget of a male Ruby-throated Hummingbird in mid-September.

The gorget of a male Ruby-throated Hummingbird in mid-September consists mainly of older orange feathers with a few fresh red ones.

Note 1: This post is about orange throats in normally red-throated male Ruby-throated Hummingbirds. If you’re trying to identify a hummingbird with an orange throat, start with Rufous Hummingbird. For additional hummingbird ID help, please refer to A Field Guide to Hummingbirds of North America in the Peterson Field Guide Series.

Note 2: This is a blog post, not a peer-reviewed article, and I’m personally acquainted with the people mentioned. Therefore, I’m dispensing with the artificial formality of referring to them by their last names.

The late-season color shift in hummingbird gorgets, a phenomenon familiar to hummingbird banders, has caught the attention of David Sibley. Unfortunately, a red herring had David barking up the wrong tree (it was an arboreal herring).

The source of the misdirection is an article in the September 2009 issue of Birding, “The Alternate Plumage of the Ruby-throated Hummingbird,” in which Donna Dittman and Steve Cardiff documented late summer/early fall molt (another phenomenon well known among hummingbird banders, though apparently none were consulted for the article). Extrapolating from Donna and Steve’s contention that Ruby-throated Hummingbirds undergo a more-or-less complete fall molt into “alternate” plumage (only to molt again in late winter—a dubious scenario), David hypothesized that the orange gorget color observed in some male Ruby-throateds in fall and winter is acquired by molt and constitutes a dull winter plumage. Comments from hummingbird banders Cathie Hutcheson and Scott Weidensaul encouraged him to reconsider, but I’d like to take this opportunity to review what we do and do not know about seasonal color changes in hummingbirds.

Though they don’t fade in the way pigment-produced colors do, the iridescent colors of hummingbirds do change over time. The exact mechanism by which this happens has yet to be documented (at least in published form), but the short answer is that it involves wear and/or bleaching rather than an additional complete molt.

To get to the long answer, it helps to know a bit of the science behind the colors. Iridescence is produced by thin layers of substances of different refractive indices, such as a film of oil on water. The refractive index is the speed at which light passes through a substance; it’s responsible for the bent appearance of a pencil in a glass of water. Refractive index values are based on the speed of light through a vacuum, which is assigned a value of 1. The higher the number, the slower the speed. The refractive index of air is 1.000293, water’s is 1.3330, and that of ordinary glass ranges from 1.523 to 1.925.

In the feathers of hummingbirds, layers of microscopic bubble-filled discs of melanin, known as platelets, are the primary source of the refractive and interference effects that create the birds’ brilliant colors. According to Crawford Greenewalt (1960), the refractive indices of the melanin and the bubbles are 2.2 and 1.0, respectively. Different colors are produced by variations in the relative thicknesses of the melanin matrix and the bubbles (the average refractive index). Thicker melanin (higher average refractive index) pushes the iridescent color toward the red end of the spectrum; larger bubbles (lower average refractive index) push it toward the violet end. Using a spectrophotometer, Greenewalt found an average refractive index of 1.85 for hummingbird feathers that iridesce red and 1.5 for those that appear blue. Following the order of colors in the spectrum, a green feather’s average refractive index would fall between 1.5 and 1.85, while the value for a violet feather would fall below 1.5.

Anna's Hummingbird gorget showing wear

Anna’s Hummingbird gorget showing shift to coppery orange on exposed distal portions of the feathers and retention of fresh hot pink color on basal portions protected by overlying feathers.

In his follow-up post, David points out that a change in wavelength from red to orange would require a change in the thickness of the platelets. He imagines this as a collapse, but physical abrasion and/or degradation by exposure to sunlight seem like far more plausible explanations. This is supported by detailed examination of individual feathers, which show a color shift on more exposed parts and the original color on more protected parts (illustrated in the photo at right).

The change in refractive index may result from thinning of the feather’s outer layer of transparent keratin (refractive index = 1.56; Osorio and Ham 2002), complete removal of the keratin layer and abrasion of the melanin matrix of the top layer of platelets, or changes in porosity that alter the refractive index of the keratin and/or melanin. Any of these would lower the average refractive index of the iridescent structures and push the color toward the violet end of the spectrum. Over time, a feather that started out bright red would be expected to shift to orange, yellow, and perhaps even green as more of the higher refractive index material (melanin and/or keratin) is removed or degraded, and that’s what we see in nature (even in the less intense green iridescence of the back feathers, which tend to be more golden green in spring and more emerald in fall).

There’s little doubt among hummingbird banders that the shift from longer to shorter wavelengths is the result of wear and aging rather than molt, but only electron microscopy of fresh and worn feathers can reveal the mechanism responsible. I don’t personally have the resources to pay for specimen preparation and EM imaging, but if someone with deeper pockets and/or university connections can provide the microscopy services I’m sure I can round up some feathers.

Addendum 1: Another photo of a male Anna’s showing the color contrast between extremely worn and new crown feathers.

Anna’s Hummingbird crown in early fall, during replacement of gorget and crown feathers.

Addendum 2: A macro photo of a male Anna’s gorget at the beginning of gorget molt. The purple/fuchsia feathers at the bottom edge are new. The color shift on the older feathers is most dramatic on the barbs, which are more exposed than the barbules.

Anna's gorget molt and wear

Click on the image to view at full resolution. ©2015 Sheri L. Williamson.

References:

Dittmann, D. L. and S. W. Cardiff. 2009. The Alternate Plumage of the Ruby-throated Hummingbird. Birding 41: 32–35. Part 1 Part 2

Greenewalt, Crawford. 1960. Hummingbirds. (Dover reprint, 1990.)

Osorio, D. and A. D. Ham. 2002. Spectral reflectance and directional properties of structural coloration in bird plumage. Journal of Experimental Biology 205, 2017–2027. link

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Out the Window preview: July/August 2011

Here’s your bimonthly teaser for my “Out the Window” column in WildBird magazine:

It was a cool but sunny morning during fall migration, and the yard was bustling with bird activity. Hordes of ravenous Lesser Goldfinches swarmed the thistle sock, a dozen Gambel’s Quail queued up to drink at the water feature, a handful of White-crowned Sparrows scrounged seeds dropped by the resident Pyrrhuloxias and Curve-billed Thrashers, and four descendents of Red Junglefowl—our pet hens Joni, Bonnie, Grace and Pearl—chased grasshoppers, scratched in the dirt, and basked in the autumn sun.

Chickens in a birding magazine?!? Equal-opportunity bird lovers who are not yet subscribers to WildBird can use this link to Amazon.com to get six colorful, information-packed issues (a full year) and benefit the conservation and education programs of the Southeastern Arizona Bird Observatory (SABO). Single copies of Wildbird are also available at newsstands and bookstores.

You’ll find subscriptions to WildBird and other birding magazines plus field guides, feeders and accessories, seeds for hummingbird-friendly plants, and more at SABO’s online shop, The Trogon’s Nest, powered by Amazon.com. Father’s Day is June 19shop now for that bird-loving dad or granddad!

Birds + clay + Arizona = FUN!

I recently connected with a kindred spirit in master polymer clay artist Carol Simmons. Carol also shares my passion for nature in general and birds in particular, so it didn’t take much wheedling and prodding on my part to convince her to team up for a clay + birds workshop in southeastern Arizona next April May!

Carol will share her techniques for creating and using her exquisite intricate cane veneers, and I’ll lead optional low-key, beginner-friendly bird walks and field trips. Casa de San Pedro Bed & Breakfast has been tapped to host the workshop, and early April mid-May birding along the San Pedro River is a colorful and inspiring experience (so are the breakfasts!).

For more information as the workshop develops, please bookmark Carol’s class and workshop schedule.

UPDATE: The workshop is scheduled for May 13-19, 2012 at Casa de San Pedro Bed & Breakfast. Fees and registration information to follow.

Ash Canyon Bed & Breakfast: an endangered hummingbird hot spot

A female Lucifer Hummingbird, one of Ash Canyon B&B's star attractions

Hummingbird enthusiasts and other bird lovers around the world have been following the complex and contentious controversy over access to Ash Canyon Bed & Breakfast in southeastern Arizona.

Resentments that had apparently been festering for years erupted after the Cochise County Planning & Zoning Commission granted owner Mary Jo Ballator a special-use permit to formalize the day-visitation portion of her operation. Owners of several neighboring properties responded by filing an appeal to have the permit revoked.

Yesterday, the county commissioners held a hearing to consider this issue. The neighbors were allowed to air their objections, including irrelevant complaints about trespass by hunters and hikers and transparently self-serving claims that 1) feeding is harmful to birds(!), 2) the Plain-capped Starthroat that summered with Mary Jo in 2002 and 2003 was a random, one-time thing(!!), and 3) Lucifer Hummingbirds can be seen in many locations(!!!).

I wasn’t the only member of the audience flabbergasted when one complainant took the stand with a copy of A Field Guide to Hummingbirds in hand, sticky notes marking passages he hoped would support these claims. When my turn came to testify, I spent most of my precious three minutes refuting disinformation and defending my book’s integrity instead of praising Mary Jo’s exemplary hospitality to both birds and people.

Despite expert testimony and passionate testimonials from many members of the birding community (including over 350 letters of support), the issues of traffic, noise, privacy, trespassing, and easement interpretations remained, and the commissioners voted 2-1 to revoke the permit. There’s still hope that a compromise can be worked out to allow Mary Jo to continue welcoming visitors while reducing their impact on neighbors. Otherwise, the easement issue may end up being decided in court.

For the time being, Mary Jo will continue to welcome her friends in the birding community on a limited basis. She now has only 6 parking spaces and can no longer accommodate RVs or buses. With this change in operations comes a reduction in income, so Mary Jo needs our support more than ever. If you’re lucky enough to visit her yard this spring or summer, please make a generous contribution to the feeder fund.

Though I doubt she’ll ever see this post, I’d like to thank (again) Bisbee’s representative on the Cochise County Board of Supervisors, Vice-Chair Ann English, for casting the sole vote in support of Mary Jo and against the appeal.

A lily-trotter by any other name

A Northern Jaçana in Belize

Pedantry loves company, so I was glad to see Julie Zickefoose setting the record straight on how to pronounce “jacana.” In the world of bird-naming mistakes, this one seems relatively minor, but it’s a headache for those of us lucky enough to travel in the Neotropics.

At issue is something that’s missing from the “c” in most renderings of the name: a cedilla, which in the Portuguese transcription of the bird’s Tupi name (jaçanã) indicates that the letter is pronounced as “s,” not “k.” When Linnaeus transcribed the name into Latin, he should have changed the “ç” to an “s.” He didn’t. Neither did anyone who came after him, so now we’ve got English speakers pronouncing it as “jah-KAH-nah,”  “juh-CAN-uh,” or “juh-KAY-nuh,” Spanish speakers and bilinguals pronouncing it as “ha-KAH-nah,” and rare pedants such as Julie and me sticking to our guns with variants on “zhah-suh-NAH.”

Having to explain yourself every time you use the original pronunciation is the pits, so I resolved for last month’s Belize tour that I would finally give up trying to pronounce it correctly. It would be “ja-KAH-nah” for my group, “ha-KAH-nah” for Spanish-speaking acquaintances.

It didn’t work out that way. The Brazilian pronunciation kept slipping out, and I sounded like a complete idiot trying to change it in mid-word to the Anglicized or Spanglicized versions (“Look, there’s another Zha… Ha… Jah…”). It’s not like Northern Jaçanas are rare in Belize, either. They’re thick around slow-moving fresh water, especially as the dry season shrinks the lagoons. After a couple of days around Crooked Tree Sanctuary, I was dying to get into the forested uplands just to get away from having to pronounce that name. No luck there, either. A living room-sized puddle along the road out of our upland lodge had a resident juvenile, so we saw at least one almost every day for the first week of the trip.

There’s an alternative that I wish would catch on: lily-trotter. Sure, it’s a little silly, but it’s in use in Africa (where a Tupi word seems out of place), every English speaker will know instantly how to pronounce it, and it fits so nicely with all the other hyphenated bird names in the tropics.

Northern Lily-trotter. On my next Belize trip, that’s what I’m calling them. No more “Zha… Ha… Jah….” Seriously.

A tale of two tanagers

Red-throated Ant-Tanager

A male Red-somethinged Ant-Tanager

I’m in Belize right now getting reacquainted with some old friends and nemeses.

One big frustration in birding down here is that bird diversity in the tropics seems to have exhausted the descriptive powers of pioneering tropical naturalists. Ant-tanagers, for example. There are two species in Belize: Red-crowned and Red-throated. Their shared last name is informative, as they’re related to and resemble the more familiar Summer, Scarlet, and Hepatic tanagers, and they follow army ant swarms.

If you thought their first names might be equally helpful, however, you couldn’t be more wrong. The male Red-crowned also has a red throat, and the male Red-throated (shown above) also has a red crown. The females have neither red crowns nor red throats, of course.

One way to tell males of the two species apart is by the color of their faces. In the Red-crowned, the area between the eye and the base of the bill—the lores—is red, while in the Red-throated the lores are dark.  Why not change at least one of the names to reflect this distinction? It’s not like it would be the first time a bird was named for an obscure bit of anatomy (Black-vented Oriole? Crissal Thrasher?) or even after its lores (there’s a whole slew of examples).

“Dark-lored Ant-Tanager” might not completely end the confusion, but at least it would be a more entertaining kind of confusion  (for Star Wars geeks, anyway).

Dark Lord Ant-Tanager??

“Out the Window” Preview: May/June 2011

Hummingbirds rule the May/June issue of WildBird, and here’s a sneak peek at my “Out the Window” column:

Fish gotta swim. Birds gotta fly. Hummingbirds gotta fight. It’s just part of who they are, but some people have a hard time coming to terms with that. Our dinner host was one of those people.

“I just love my hummingbirds!” she gushed. “They’re so cute and sweet.”

My husband smiled politely, but before he could respond her eyes narrowed. In a tone that left no room for discussion, she said, “People say they’re fighting, but I think they’re just playing.”

Forkfuls of tender greens paused between plates and mouths, dripping vinaigrette. Tom and I dared not even exchange glances.

If you’re intrigued and not yet a subscriber, this link to Amazon.com will get you six colorful, information-packed issues (a full year), and your purchase will also benefit the conservation and education programs of the Southeastern Arizona Bird Observatory. Single copies of Wildbird are also available at newsstands and bookstores.

You’ll find WildBird and other birding magazines plus field guides, feeders and accessories, seeds for hummingbird-friendly plants, and more at SABO’s online shop, The Trogon’s Nest, powered by Amazon.com.

“Out the Window” preview: March/April 2011

Here’s a teaser from my “Out the Window” column in the March/April 2011 issue of WildBird magazine:

Cactus Wren. Say’s Phoebe. Cassin’s Kingbird. Western Tanager. Killdeer. Curve-billed Thrasher. American Kestrel. Bullock’s Oriole.

Dawn was barely breaking, and it sounded like someone was playing A Field Guide to Western Bird Songs at top volume outside our bedroom window.

Ordinarily I enjoy birding by ear, but after working on a project into the wee hours of the morning I needed a little more face time with my pillow. Rolling over, I pulled back the curtain and squinted up at the slim form silhouetted atop the mesquite tree…

Not a WildBird subscriber yet? This link to Amazon.com will get you six colorful, information-packed issues (a full year), and your purchase will also benefit the conservation and education programs of the Southeastern Arizona Bird Observatory. Single copies of Wildbird are also available at newsstands and bookstores.

You’ll find WildBird and other birding magazines plus field guides, feeders and accessories, seeds for hummingbird-friendly plants, and more at SABO’s online shop, The Trogon’s Nest, powered by Amazon.com.

“Out the Window” preview

Here’s a teaser from my “Out the Window” column in the January/February 2011 issue of WildBird magazine:

Hi, my name is Sheri, and I’m a sparrow-phobic. I used to get queasy at the mere thought of identifying those “little brown jobs.” For the first three decades of my birding career, the sparrow section of my life list would have been almost blank if not for towhees, juncos, and the “skunkheads” (White-crowned and White-throated).

I was finally forced to admit that I had a problem when I moved from the relatively sparrow-free Huachuca Mountains to the sparrow-infested desert…

Not a WildBird subscriber yet? This link to Amazon.com will get you six colorful, information-packed issues (a full year), and your purchase will also benefit the conservation and education programs of the Southeastern Arizona Bird Observatory. Single copies of Wildbird are also available at newsstands and bookstores.

You’ll find WildBird and other birding magazines plus field guides, feeders and accessories, seeds for hummingbird-friendly plants, and more at SABO’s online shop, The Trogon’s Nest, powered by Amazon.com.

Fawn-breasted Brilliants in combat

Here’s an interesting observation of an unusually prolonged battle between two large tropical hummingbirds, posted by Dennis Arendt, Lelis Navarete, Kit Larsen, Roger Robb, and Leon Esthleman to NEOORN-L, a listserv for ornithologists working in the Neotropics, and cross-posted to HUMNET (reformatted for ease of reading):

A male Fawn-breasted Brilliant photographed on my December 2009 trip to Ecuador

A male Fawn-breasted Brilliant photographed on my December 2009 trip to Ecuador

On 5 October, 2010, at the hummingbird feeding station at Cabañas San Isidro east of Quito, Ecuador, two male Fawn-breasted Brilliants fell to the ground together. They appeared to have their feet intertwined and their bills were jabbing each other. It was 15:31 and a light rain had begun.

They stayed quiet in the wet grass with one bird on top of the other. Both birds had their wings extended fully. The bird on top had its long bill stuck into the neck feathers of the bird underneath. The bird dominating the other would move its bill from the neck to the wing, probing and sometimes grabbing feathers.

After about ten minutes, the bird underneath would fight to release himself from the bird above. They flopped sideways and moved a few centimeters, but the dominating bird stayed on top. They would stay quietly in the grass for several minutes, then the struggle would be repeated with the same results.

The rain grew heavy and this struggle continued for one hour and forty minutes. At 17:11 the dominating bird flew up to a sugar water feeder and sat on top, not on the perch, and drank for half a minute. Then it flew away.

The other hummingbird was picked up from the wet grass. It was thoroughly wet, but alive, and showed no indications that its flesh had been pierced by the other bird’s bill. The defeated bird would surely have died without help. It was taken back to the kitchen at Cabañas San Isidro where it was warmed and fed sugar water. It too flew off after about fifteen minutes.

Emphasis added to highlight additional evidence of the inadequacy of a hummingbird’s bill as a weapon. Poking? Yes. Grabbing? That too. Piercing? Not so much.

Related posts on this topic:

Killer hummingbirds?
Search of the Week: “hummingbird attack eyes”