posted January 25th, 2012; last edited January 25th, 2012 –– David Sibley Thanks to reader Anne DuPont for sending in these photos of a pair of Great Blue Herons at Wakodahatchee Wetlands, Delray Beach, Florida. It’s clearly a mated pair, but the female (sexed by behavior) has more white on the head and fore neck, paler legs and bill, white head plumes, paler rust color on the upper legs and shoulder, and probably a few other things.
I’ve written about Great Blue and “Great White” Herons before here, and noted that in the Florida Keys most birds are white, some are dark, and there is a continuum of variation in between, so it’s not a surprise to see a bird that looks about 75% dark, 25% white. Delray Beach is about 60 miles north of the expected range of “Great White” herons, however, and this pale individual suggests that the zone of intergradation may be more extensive than I thought. It’s worth looking carefully at other nesting Great Blue Herons in southern Florida to see how far the apparent “Great White” influence extends.
 Typical Great Blue Heron (left) and slightly paler Wurdemann's variant. Photo copyright Anne DuPont, used by permission.  Typical Great Blue Heron (back) and slightly paler Wurdemann's variant. Photo copyright Anne DuPont, used by permission. And did you identify the second species of bird in the two photos?
posted January 24th, 2012; last edited January 24th, 2012 –– David Sibley 
The sturdy box contains one hundred cards, each showing one species of commonly seen bird on the front, with details of habits, identification, and range on the back of the card.
Click to view on Amazon.com:
Sibley Backyard Birding Flashcards: 100 Common Birds of Eastern and Western North America
Or click for info from the publisher – Random House
posted January 23rd, 2012; last edited January 23rd, 2012 –– David Sibley  Snowy Owl. Original gouache painting copyright David Sibley. Published on the cover of the Journal of Raptor Research 2011. Snowy Owls are making news this winter, as in the New York Times today (link)
The conditions setting up this invasion started at least a year ago. Last summer, burgeoning lemming populations in the arctic provided abundant food for nesting owls, which were able to feed and fledge five or even seven young per nest instead of the more normal zero to two. Once this population explosion of young owls got out hunting on their own in fall 2011, the demand for lemmings outstripped the supply, and when winter set in food got even scarcer.
Dominant adult birds set up feeding territories and defend them against all other owls (including their own offspring). They have to protect their own food supply. As food got scarcer last fall the adults defended ever-larger territories and the lower-ranking young birds were forced to forage in less productive areas, or sneak around and try to poach on adult territories.
A shortage of food has been shown to stimulate a bird to start depositing fat and to increase their migratory restlessness, and in species with a pecking order or social hierarchy the low-ranking birds are the first ones to feel the food shortage (Terrill 1987). Therefore the low-ranking owls that were having a hard time getting enough food found their bodies automatically preparing and urging them to “hit the road”.
And they moved south; some are near starvation and some better off. Some will survive and return to the arctic in the spring, and if all goes well they will never have to come this far south again in their lifetime.
References
Terrill SB. 1987. Social dominance and migratory restlessness in the dark-eyed junco (Junco hyemalis). Behav Ecol Sociobiol 21:1–11 Link – this research was on captive Dark-eyed Juncos, but let’s assume Snowy Owls are similar
posted January 20th, 2012; last edited January 20th, 2012 –– David Sibley The Sibley eGuide to birds was recently adapted for the Kindle Fire tablet (and still works on other Android OS devices). You can find it at the Amazon app store.
In other news an update for the Android OS is coming soon that will (among other things) remove the annoying requirement to verify over the network every 45 days, so the app will be fully functional and never need a network connection except once when it is installed.
Also, the developers tell me to expect an announcement about a Windows Phone 7 version soon.
Screen Shots:
 Broad-tailed Hummingbird as it appears on the Kindle screen.  Magnificent and Broad-billed Hummingbirds using the "compare" feature in landscape mode on the Kindle Fire.
posted January 20th, 2012; last edited January 20th, 2012 –– David Sibley Like many other species of ducks that are distinguished by head shape, Common and Barrow’s Goldeneyes are at least as easy to tell apart when sleeping as when they are awake. Birds that are awake and active change head shape a lot as they go from relaxed to alert to diving, but sleeping birds are always about the same. The image below shows the typical appearance of the two species. If you like quizzes you can try to identify them before you read the next paragraph, or just read on for the answer.
 Two species of female goldeneyes showing differences in head shape. See text for identification and discussion. Original gouache painting copyright David Sibley. Differences in head shape mainly involve the placement and shape of the peak of the head. On Barrow’s the peak is farther forward, and the crown is low, flat, and sloping back to the “mane”. On Common the peak is farther back and taller, rising from the forehead to a rounded triangular peak, then sloping sharply down to the “mane”. In addition, the forehead of Barrow’s is a little steeper and bulging, and the “mane” of Barrow’s is a little longer, all combining to make the head look low and oval, while Common has a more triangular or circular head. In the painting here it’s Common above and Barrow’s below.
If only they would sleep more often…
posted January 19th, 2012; last edited January 19th, 2012 –– David Sibley  The underside of the tail of four different American Goldfinches - two males and two females. See text for details. Photographs of birds trapped for banding in Concord, MA, copyright David Sibley. For much of the year, distinguishing male and female American Goldfinches is easy (when the males show their brilliant yellow summer plumage, about March through September). Even in January and February many males have a few bright yellow feathers showing, but otherwise the gray-brown nonbreeding males can be hard to tell from females. There is very little difference between immatures and adults of each sex.
Males have really black wings with bright wingbars and feather edges, while the females have duller brownish-black wings with buffy or brownish-white wingbars and edges. This is pretty easy to judge, but it requires a bit of experience and judgment.
For a more objective and reliable difference, look at the underside of the tail, which is easily seen when birds are sitting on a feeder. Males have blackish tail feathers with well-defined white spots, females grayish feathers blending into dull white spots. Once you’ve confirmed the sex of a bird by the tail pattern, take a minute to look at the wings, the body plumage, bill and leg color, etc., and you’ll soon become an expert on goldfinch plumage variation.
posted January 17th, 2012; last edited January 17th, 2012 –– David Sibley There are four named subspecies of Scaled Quail, three in the US and one in Mexico. The subspecies found in southern Texas is distinctly different from the other three, at least in adult male plumage, and makes the list of field identifiable subspecies. Here’s a quick summary of the differences, based on study of specimens at Harvard’s MCZ, and numerous photos. Some field testing is needed, and figuring out where (and how much) the subspecies intergrade is important. No difference in voice has ever been mentioned, but that’s worth checking out.
Basically, any bird with a chestnut belly is safely identified as the south Texas subspecies castanogastris. Birds without a chestnut belly could be another subspecies, or females or immatures of castanogastris, and you’ll have to look at other details to identify them. Vagrants are unlikely to occur, so range will be a reliable clue to identification, but in order to work out the range we’ll have to identify a lot of birds…
 Males of the two forms of Scaled Quail found in the US: pale-bellied subspecies pallida and hargravei (left) in most of the species' range, and chestnut-bellied subspecies castanogastris (right) found in southern Texas. Original gouache panting copyright David Sibley. Males differ very slightly in overall color and darkness, probably not enough to be useful in the field except in direct comparison (which is unlikely to happen in the wild). Identification will have to be based on the color of the belly and undertail coverts.
Males: southern Texas vs Arizona-New Mexico
- center of lower belly with dark chestnut or maroon-brown patch, may be small or irregular (vs center of belly pale buff)
- belly surrounding chestnut patch tinged strongly orange-buff, fading to cream-buff outwards (vs slightly orange-buff in center of belly where TX birds have chestnut, fading to off-white outwards)
- undertail coverts with dark brownish markings, washed orange-brown to rust (vs paler gray-brown markings with cream-colored edges)
- neck and breast darker gray, forming distinct gray breastband
- crown and cheeks grayer and darker (vs ashy brown)
- slightly darker overall
- slightly darker and more brownish on back
- tail darker gray above
- throat slightly darker and more orange-brown
Females differ very slightly in overall color similar to male but less obvious, and south Texas females don’t really show any trace of the chestnut belly patch, so the best field mark for males is not useful on females. They do seem to show a difference in throat pattern.
Females: southern Texas vs Arizona-New Mexico
- throat distinctly streaked (vs smooth pale buff-gray)
- belly and under tail coverts slightly more orange toned
- breast and neck very slightly darker
- upperparts darker and warmer brown, especiaily on scapulars and upper tail coverts
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.
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