posted January 13th, 2012; last edited January 13th, 2012 –– David Sibley A recent discussion on the ID-Frontiers listserver involved an immature gull photographed in Utah (photo by Norman Jenson here). The consensus (and I agree) is that it is a Western Gull based on plumage and shape. But questions arise from the fact that it looks barely larger than the California Gulls next to it – abnormally small for a Western Gull.
Those of us who didn’t see the bird in life might like to ignore the apparent size as an illusion of the photographs, but the observers report that the bird really did look small. Can it still be a Western Gull? Yes. Since size is the only thing suggesting that it’s not a Western Gull, I think we have to go with the identification as a very small Western Gull. But is it a “dwarf”, or just the small extreme of normal variation?
Terminology
Much of the discussion about this bird and other unusually small individuals has referred to them as “runts”, but technically that is the wrong term. A runt usually means a young animal, still growing (the smallest of a litter of puppies, for example), that is smaller than its siblings. This is common in birds, caused by poor health or poor nutrition, but if runts survive they can grow to full size indistinguishable from their nest-mates. Unusually small adult birds should be called “dwarfs”.
Peter Pyle reported on ID-Frontiers that gull expert Larry Spear held the opinion that there is no such thing as a dwarf bird, and that an individual like the Utah gull is just the rarely seen tail end of normal variation in Western Gull. In the same way that full-grown humans under five feet (or over seven feet) tall simply represent the extremes of normal variation.
In humans dwarfism is neither well-defined nor simple. Dwarfism is defined by an arbitrary threshold along the continuum of adult sizes, and over 200 causes of dwarfism have been identified (Wikipedia). It seems likely that birds are similar.
An informative study by Hicks (1934; thanks to Steve Mlodinow for the tip) carefully examined over 10,000 starlings in the hand. Unusually small and large birds that caught the researchers’ attention were measured. In this sample of 10,000 birds there were seven “giant” and six “dwarf” individuals that measured about 10% larger or smaller than the average of “normal” birds measured.
Unfortunately not all 10,000 birds were measured, only about 500 randomly selected “normal” birds were carefully measured, along with the 13 individuals that were strikingly large or small. Only total length measurements are given, but the largest dwarf measured only 9mm (about 5%) smaller than the smallest “normal” female. Furthermore, all of the giant birds were males (the larger sex), and five of the six dwarfs were females. It seems likely that, if all 10,000 individuals had been carefully measured, the data would fill in the relatively small gaps between the normal birds and the dwarf and giant birds.
Another documented case, with direct application to identification, is that of an unusually small Great Crested Flycatcher trapped and collected in New Jersey (Murray, 1971). This individual was immediately suspected of being an Ash-throated Flycatcher based on size, but careful study confirmed it to be a very small Great Crested. Its measurements are over 10% smaller than the average for Great Crested, and smaller than the minimum given by Pyle (1997). It is even a little too small for Ash-throated Flycatcher! In addition, it has a disproportionately short tail, while its wing measurement is just 1mm below the minimum for Ash-throated, its tail measures 9.5mm shorter than the smallest Ash-throated measured by Pyle.
It’s really a semantic question. Documented cases of unusually small birds exist and must be considered when identifying rare species. We could set an arbitrary threshold that categorizes them as “dwarfs” or just consider them the extremes of normal variation. The impact on bird identification is the same either way.
References
Coulter, M.C., 1982. Development of a Runt Common Tern Chick. Journal of Field Ornithology, 53(3), pp.276–279.
Hicks, L.E., 1934. Individual and sexual variations in the European Starling. Bird-Banding, 5(3), pp.103–118.
Murray, B.G., 1971. A Small Great Crested Flycatcher: A Problem in Identification. Bird-Banding, 42(2), pp.119–119.
Pyle, P. et al., 1997. Identification Guide to North American Birds: Columbidae to Ploceidae, Slate Creek Press.
posted January 12th, 2012; last edited January 12th, 2012 –– David Sibley There are still a few places left on my 2012 birding workshops 27 May to 8 June 2012 at Pine Butte Guest Ranch in Montana. It’s a great opportunity to visit a spectacular place, learn some birding skills and techniques, meet some nice people, and support the work of The Nature Conservancy
 In 2010 we were lucky enough to find a family of Northern Hawk-Owls, including this fledgling, establishing one of the southernmost nesting records in North America. Photo copyright David Sibley. During the week we’ll spend our days in the field, and evenings at the lodge. And we’ll have informal discussions and a couple of more formal presentations about things like how to draw birds, identifying birds by song, the psychology of perception and bird identification, bird topography, molt and plumages, wing shape and flight, and more.
 Lazuli Buntings nest in willow and aspen thickets along the river and also around mountain meadows. Photo copyright David Sibley.  A male Rufous Hummingbird moves to defend its feeder, which happens to be on the porch of the Pine Butte Guest Ranch. Photo copyright David Sibley. I’ll be joined for part of the time by John Carlson, an excellent ornithologist and photographer from Montana, and also by artist and birder Keith Hansen, from Bolinas, California, and it promises to be a really fun time.
 The main lodge at Pine Butte Guest Ranch. Right around the building it's common to see Mountain Bluebird, Rufous Hummingbird, Western Tanager, etc. Black Bear and Grizzly Bear have been seen occasionally on the ridge visible behind the lodge. Photo copyright David Sibley.
We spend a lot of time hiking (short distances), but the pace is relaxed, with early morning birding right around the ranch, short drives, no change of lodging, and no real “target” species, which allows time to study and discuss whatever bird is cooperative – a Red-necked Grebe, Rufous Hummingbird, or Raven all provide opportunities for learning. The food and accommodations are excellent, and the setting is unmatched.
I hope you can join us! More info.
 This is some of the wildest and most scenic land in the lower 48 states. This photo is taken from the top of Pine Butte, looking west towards the Rocky Mountain Front (where the ranch is located). Habitat ranges from prairie grassland and fen wetland, through Limber Pine, Douglas-Fir, Spruce-Fir forest, and up to treeline, all within a space of a few miles, and the birds are just as diverse.
posted December 7th, 2011; last edited December 8th, 2011 –– David Sibley Recent discussion of the identification of a white goose in Ohio (beginning here) prompted me to put together some sketches of bill shapes of Ross’s and Snow Geese, since bill shape is the most significant difference between those species. It was a very interesting exercise, as each species is surprisingly consistent in the relative size and proportions of head and bill, suggesting that the overall impression of bill size is a fairly reliable (though subjective) feature, and there are some other details that allow a more objective identification.
 Tracings of head and bill shapes of white geese, adjusted so head sizes match, to emphasize differences in proportions. Original pencil sketches copyright David Sibley. The middle column of presumed hybrids is traced from three individual birds. In the middle is one from Kentucky (photograph by David Roemer here) that seems to be a straightforward intermediate bird and almost certainly a hybrid. The upper presumed hybrid is from Oklahoma, the smallest-billed of the three (traced from a photograph by Victor Fazio here) and the bottom presumed hybrid is the contentious Ohio individual (traced from a photo by Matt Valencic here).
Besides absolute bill size, the features that seem most useful for distinguishing Ross’s from Snow and from potential hybrids are:
- faint or absent “grin patch” – Ross’s usually show a small and inconspicuous dark line, Snow Geese an obvious black oval. This is related to the following…
- lower mandible nearly straight on Ross’s, strongly curved on Snow, and slightly curved on hybrids
- border of feathering at base of bill relatively straight on Ross’s, curved on Snow – this is somewhat variable in Ross’s, and seems even more variable in hybrids (if these three are really hybrids), but Snow always has the border strongly curved, and Ross’s straight or slightly curved.
- As a measure of bill length, on Ross’s the bill is always obviously shorter than the thickness at the top of the neck, on Snow the bill length is greater than neck thickness, and hybrids intermediate.
- Round head – There is little difference in forehead slope, but Ross’s show a high rounded crown so that head of Ross’s can be described as a circle, while on Snow Goose (and hybrids) the head is more oval.
I still maintain that the Ohio bird fits into the “hybrid” column better than the Ross’s column. There must be backcrosses and maybe even pure Ross’s Geese that blur the distinction between these categories as illustrated, and discovering that will require a more detailed study of variation in a large number of geese. Hopefully these sketches will help the discussion move forward.
posted December 7th, 2011; last edited December 7th, 2011 –– David Sibley 
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posted December 5th, 2011; last edited December 5th, 2011 –– David Sibley The Sibley eGude to Birds for iPhone and iPad has been updated to be a universal app. The new version takes advantage of the full screen of the iPad to show images and maps at high resolution, show all information (images, text, map, and audio) on a single screen, and in landscape orientation allows viewing the species list and species account at the same time for quick navigation.
 Rose-breasted Grosbeak in the new iPad layout with images, text, map, and audio all together. Scroll up and down to see all images. Tap any image or map to view full screen. Swipe left or right to see previous or next species.  The iPad version in landscape orientation comparing Black-headed and Rose-breasted Grosbeaks. You can scroll the images of each species independently up and down, swipe left or right for previous or next species, and select any other species from the list on the left. Tapping any image shows it full screen. Other projects in the works include a version for Windows Phone 7, a version for Amazon’s Kindle Fire, and various minor improvements to content and navigation.
A few users have reported issues with the new version on the iPod Touch. If this is you please contact us and we’ll get it sorted out. Also note that the update might wipe out any bird list records you have in the app, so make sure you download those and save them before installing the new version. At this time we recommend using the listing function in the app only for temporary record-keeping because of this, for example to keep a list for a day or a trip, then download that data and archive it in another program.
The 2011 name changes announced by the AOU will appear in the next update.
posted October 27th, 2011; last edited October 27th, 2011 –– David Sibley A recent article by Tim Enthoven in the New York Times – Don’t Blink! The Hazards of Confidence – offers some fascinating thoughts on judgment, expertise, and illusions of confidence, and it’s an interesting perspective from which to examine the challenge of bird identification.
One of his key points is that confidence does not arise from a careful assessment of probabilities.
“Confidence is a feeling, one determined mostly by the coherence of the story and by the ease with which it comes to mind, even when the evidence for the story is sparse and unreliable. The bias toward coherence favors overconfidence. An individual who expresses high confidence probably has a good story, which may or may not be true.”
Our confidence in bird identification is often based on fleeting glimpses, subjective impressions, and snap judgments, yet we still say we are “one-hundred-percent sure”. This confidence, according to Enthoven, comes from the tidy narrative we construct around our sighting, more than from the actual observation. The real danger of this confidence is that it prevents us from recognizing our mistakes. Overconfidence leads us to reject the possibility of error and instead adapt our story to emphasize our correctness. Overconfidence, ironically, can be one of the biggest barriers to developing expertise.
Admitting mistakes forces us to reconsider and rewrite the narrative, and we get better at bird identification by developing a richer and more nuanced library of scenarios to describe our sightings. In his conclusion Enthoven says: “True intuitive expertise is learned from prolonged experience with good feedback on mistakes.”
In other words, the best way to develop true expertise as a birder is to spend long hours in the field, to be alerted to your mistakes quickly, and to review them unflinchingly. Unfortunately, most of our mistakes as birders disappear into the distance, and we never have a clue that a mistake was made, let alone what it might have been. The ones we do know about are often pointed out by other birders, and at that point most people get defensive.
That’s normal, but also counterproductive. Mistakes happen, and they provide excellent learning opportunities, but only if we are open to admitting and examining them.
posted October 26th, 2011; last edited October 26th, 2011 –– David Sibley In a recent post at the ABA blog, a new smartphone app is described that promises to help identify bird songs in the field. Bird song identification software has been around for a long time, mostly running on desktop computers and used for research, and the idea of having that capability in a smart phone has been a very popular future dream of many. This app would send your recording of a bird to a server (where the heavy analysis would happen) and then return the answer to your phone.
An app like this could begin to put bird song identification within reach of novices, and that’s exciting. As the developer Mark Berres said “You’ll learn more about the world around you, and there’s nothing but good in that”.
So I was surprised to read the comments on the ABA blog and find that five of the first nine are negative. Commenters are concerned that people would be interacting more with their phones than with nature, that birders won’t even have to listen to birds, won’t bother to learn the songs, etc. The common thread is that this will create a new generation of lazy birders.
The same principle has been debated for years regarding the use of calculators in schools. A good overview of that debate is here. It’s worth noting that there is no evidence that calculator use does any harm to math learning. Some of the arguments in favor of calculator use can be applied directly to this bird song app debate. For example: Calculators allow students to spend less time on tedious calculations, so those who would normally be turned off by frustration or boredom can still learn the overarching concepts of math.
If an app can help relieve some of the initial frustration that beginners experience when they try to identify a sound in the forest, that might be the difference between a good experience and a bad one. Someone who feels like they succeeded in identifying a bird will be more likely to try to identify more.
Sometime in the distant future there might be a device that will simply identify sounds as we walk, and one that we can trust enough that we simply accept its identifications. I think the fear is that birding will become just a transect through the habitat while looking at the smartphone screen and reviewing the collected data. If that happens I may change my mind about this topic, but really, I don’t think technology can ever take away the central birding experience of exploring and discovering.
For now, these early apps are going to be a bit cumbersome – you record the sound, send it to the server, wait for a response, read the list of likely answers, listen to the included reference recordings, reject all the suggestions, try to get a better recording to resend, repeat. Anyone who goes to all that trouble is actually going to learn a lot about bird songs, and will quickly graduate to leaving the phone in their pocket and identifying birds much more quickly and happily by ear. That’s not lazy. I think that sounds like a great way to learn.
posted October 25th, 2011; last edited October 25th, 2011 –– David Sibley I recently commented on this ID problem on MassBird, pointing out differences in details around the eyes.
Chipping sparrow has very distinct, narrow whitish arcs below and ABOVE the eye, contrasting with darker gray-brown feathers, and broken at front and BACK by the dark eyeline. Simply looking for these distinct white arcs is a good quick ID clue, not shared by any other sparrow. (But don’t go running to your Sibley Guide to look it up, I didn’t appreciate how useful it was until recently, so it’s not illustrated very well in the current edition)
On Clay-colored there are pale feathers all the way around the eye, and these blend into just slightly darker feathers, not contrasting at all above the eye (just a broad pale eyebrow stripe). And there is only a very weak dark eyeline breaking the eyering behind the eye.
This leads to the ‘open-faced’ impression on Clay-colored, since the eye is set in a broad pale area.
After reading my comments, Phil Brown put together a nice comparison of two photos, which you can see on his blog here: http://birdsofessex.blogspot.com/2011/10/sparrow-identification-chipping-clay.html
posted September 20th, 2011; last edited October 26th, 2011 –– David Sibley After all the discussion of orange-throated and red-throated hummingbirds, I thought it would be helpful to add a brief and simplified summary of how the brilliant iridescent colors of hummingbirds are produced. These are structural colors, not pigment, which means they are reflected by microscopic structural features of the feather surface.
 The gray bands at the bottom represent a cross-section of an air bubble in hummingbird feathers. Incoming light waves are shown in gray. Some light reflects from the upper surface of the air bubble, and some light passes through and reflects off of the inner surface as well. When wavelengths of light (red in this example) match the thickness of the air bubbles. the two reflected waves combine constructively so that light of that color is enhanced. Wavelengths (green in this example) that do not match the thickness of the air bubble are "out of sync" when they reflect off the two surfaces and cancel out. The diagram here shows how this happens. The surface of the feather is composed of layers of tiny air bubbles. When light strikes the surface of the feather, some light is reflected from the outer surface, and some light travels through the air bubble and reflects off the inner surface. Light (red in this example at right) with wavelengths that match the thickness of the air bubble are “amplified” as the reflected waves from the inner surface match up and combine with the reflected waves from the outer surface. Other wavelengths (such as the shorter green waves shown in this example) are “out of sync” when they combine after reflecting off both surfaces, and they cancel out. This is the fundamental process that creates the very pure and brilliant colors we see on hummingbirds.
This is an idealized example. In reality the structures that produce iridescent colors in hummingbirds are much more complex, with multiple layers of air bubbles. The refractive index of the material the light must pass through, along with many other factors, can alter the color that is produced, but it is the combined reflections from inner and outer surfaces of the air bubbles that creates iridescent colors. The entire system must be incredibly precise and uniform. The difference between red and orange could be a difference of a few nanometers, and one of the most amazing things about this is that there is so little observed variation in hummingbird colors.
When Ruby-throated Hummingbirds develop orange throats, that means a tiny shift to reflecting slightly shorter wavelengths of light. This could be the result of a thinner layer of air in each bubble, or a thinner layer of solid material forming the outer surface, or a slightly lower refractive index of that material, or many other possible variables.
Still lots of questions…
posted August 16th, 2011; last edited September 5th, 2011 –– David Sibley 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. ….Continue reading Progress on the orange-throated hummingbird mystery →
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