Audubon's mysteries: Carbonated Swamp-Warbler

One of the enduring mysteries of North American ornithology involves several species which were painted by Audubon in the early 1800s but never seen again. The most striking and appealing of these birds is the Carbonated Swamp-Warbler, and since the painting was published ornithologists have debated whether this could be a rare and now-extinct species, a hybrid, or merely a fantasy created by Audubon.

Audubon wrote:

I shot the two little birds here represented, near the village of Henderson, in the State of Kentucky, in May 1811. They were both busily engaged in searching for insects along the branches and amongst the leaves of a dogwood tree. Their motions were those common to all the species of the genus. On examination, they were found to be both males. I am of opinion that they were each young birds of the preceding year, and not in full plumage, as they had no part of their dress seemingly complete, excepting the head. Not having met with any other individuals of the species, I am at this moment unable to say anything more about them. They were drawn, like almost all the other birds which I have represented, immediately after being killed; but the branch on which you see them was not added until the following summer.

Despite his definitive statement that he shot two specimens, and painted them from life (well... death), there has always been speculation that Audubon may have invented these birds, or painted them from memory rather than from specimens. Audubon frequently stretched the truth, and many of his untruths are well-documented, although as Jonathan Rosen suggests in a New York Times book review they are "more like the improvisational ''stretchers'' of Huck Finn than the calculated inventions of a man on the make".

While viewing some of Audubon's original paintings at a New York Historical Society exhibit several years ago I noticed that the paintings ranged from very lovingly detailed (e.g. Carolina Parakeet) to more cursory and simplistic (e.g. Bicolored Blackbird and others painted from specimens brought back by Townsend). It occurred to me that the painting style and quality of details might provide clues to Audubon's mystery birds. The recent launch of a complete collection of high resolution scans of Audubon's plates at the University of Pittsburgh (available here) prompted me to take a closer look at this painting.

A brief survey of the painting reveals several factual errors:

• Dark stripes on the back of the lower bird are pointed at the front, broader and diffuse at the rear - opposite of the normal feather arrangement on songbirds
• Median secondary coverts (the shorter wingbar) should have the lower feathers overlapping those above; both birds have these feathers overlapping incorrectly
• Median secondary coverts on the lower bird are too long
• Too much yellow shows in a broad wedge above the forewing on the lower bird, unlike any known songbird; there is no way the feathers painted on the upper bird could be rearranged to look like the lower bird
• Uppertail coverts of the upper bird are shaped and arranged incorrectly
• There is a general lack of detail, a sort of vagueness of structure to the wingtips and tails, both birds lack primary coverts (which should be visible) and the tails are unusually short with very narrow feathers (unlike any known wood-warbler).

One could give him the benefit of the doubt and allow that these could all be due to carelessness or inexperience. I can imagine that there must have been times when he was distracted from his painting by biting insects, weather, hunger, illness, or other concerns. But checking some of his other early paintings (Chestnut-sided Warbler plate 59, Cerulean Warbler plate 49, Purple Finch plate 4, Song Sparrow plate 25, etc) shows that these are all more detailed, with correct arrangement of coverts and streaks. There are always things to nitpick, but in each of these paintings the overall draftsmanship is painstakingly accurate, and smacks of authenticity. The Carbonated Swamp-Warbler painting is subtly lacking, which leads me to conclude that Audubon was probably not looking at a bird as he painted.

This is all merely speculation and circumstantial evidence - weighing possibilities. There is no way to know for certain what Audubon painted (unless the Carbonated Swamp-Warbler were to be rediscovered and confirmed). It's possible that this species did exist, a hyper-specialized wood-warbler, like Kirtland's, that was extinguished by the first clearing of forests in the early 1800s. It's possible that Audubon did see them, and simply painted them poorly. Or that he saw one and tried to recreate it from memory some time later (lying about the two specimens to bolster the credibility of his painting). But given that the only evidence of the species' existence is Audubon's painting and written account, that evidence needs to meet high standards. I think the quality of the painting casts some doubt on his claim that he was working directly from two specimens, and then that casts doubt on the existence of the species.

A reprieve for Red Knots

Great news: New Jersey's governor Corzine yesterday signed into law a moratorium on the harvest of Horseshoe Crabs in that state (press release here). This is great news for Red Knots - politicians have finally recognized the dire situation and put the needs of a species ahead of the seasonal income of a few fishermen. This moratorium protects the knot's primary food source during spring migration. Hopefully other states (especially Delaware, Maryland, and Virginia) will follow New Jersey's example, and hopefully this action has come in time to allow the crab and knot populations to recover. See my previous post for background on the Red Knot's troubles.

Greater Redpoll photos

Maybe I should change the name of this blog to "All about Redpolls", but I've received a few photos that I wanted to pass along, making the point that "Greater" Common Redpoll is not just an eastern specialty. The AOU checklist and the BNA account report that this subspecies winters regularly from Labrador west to Manitoba, and has been recorded from Michigan, Illinois, Indiana, and Ohio, as well as Colorado!

So here are two photos from Seth Cutright of Ozaukee County, Wisconsin showing an apparent "Greater" (on the upper right). Notice the slightly larger size, larger bill, dark color, and heavy streaking especially on the nape, flanks, and throat. If this is really a "Greater", it would apparently be the first for Wisconsin, although that may not be too surprising considering the distribution of other records.

Photo copyright Seth Cutright, used by permission - click to enlarge

And (below) here it is again on the top right, turning away but showing the large size, heavy flank streaking and dark undertail coverts.

Photo copyright Seth Cutright, used by permission - click to enlarge

Cathy Mountain of Fort McMurray, Alberta also sent me a series of photos from her feeder, and among them is another apparent "Greater" Common Redpoll (far right). The large size, dark color, and heavy streaking is pretty obvious. This would apparently represent a first for Alberta, but that should not be too surprising if the subspecies really winters regularly in Manitoba.

Photo copyright Cathy Mountain, used by permission - click to enlarge

So I would urge anyone who sees Common Redpolls to watch for larger birds and try to document potential "Greater" redpolls. This subspecies appears to wander widely to the west of its breeding range, and could seemingly turn up anywhere within the winter range of Common Redpoll (at least west to the Rocky Mountains).

Another note on Hoary:
Trained observers will notice that the photo above shows several Hoaries. In fact it was Cathy Mountain's photos from Alberta that prompted me to check CBC results for my post about winter range of Hoary Redpoll. Fort McMurray is obviously within the core of the winter range of Hoary, as the following photo shows.

Photo copyright Cathy Mountain, used by permission - click to enlarge

I guess there are at least eleven Hoary Redpolls in this picture! (when I said "ten" yesterday that was just an error in addition). The seven in the foreground and one back left are so white they are pretty unambiguous - the kind of Hoaries that are seen only rarely east of the Northern Plains region. (I'm also counting the two central birds with tawny head and faint flank streaking as Hoary, as well as the partial bird visible at the top left.)

Notes:
More of Seth Cutright's redpoll photos

Greg Sargeant reports that there is a "Greater" Common Redpoll in Rhode Island, photo here, which may be the first ever noticed in that state.

Another large pale redpoll

A new photo by Dan Berard shows what looks like an intermediate large redpoll, and should be added to the discussion in my previous post.

photo copyright Dan Berard, used by permission - 7 Mar 2008, Millbury, MA

Dan says both of these birds were about the same size and both were larger than the other redpolls with them. This is interesting on its own because the paler bird looks larger in this photo. Assuming that Dan's observation is a more reliable measure of size, this shows the danger of putting too much emphasis on a single photo when judging size. [update 11 March - Dan points out that the pale bird is at the near edge of the railing, and the dark bird at the far edge, so that could account for the apparent size difference in the photo.]

The bird on the right is dark and heavily-streaked, approaching the "classic" rostrata, with heavy streaks on the breast and flanks. The bird on the left is distinctly paler and Hoary-like, with the pale gray ground color of the head and back, whitish flanks with fairly narrow streaks, etc. If the bird on the left was smaller, I would study it as a potential exilipes Hoary, but it has some odd dense fine streaking around the neck and breast, and the flank streaks are unusually broad for Hoary. It seems too pale to be rostrata, too dark to be hornemanni. Which is it?

Another note: This photo (with two large birds together) demonstrates the point that redpolls seem to travel in more or less cohesive groups within the big flocks - what we might call "subflocks". This is similar to the way geese sort out within a big flock, but the redpoll subgroups are not quite as cohesive. There have been quite a few reports this winter of small groups of redpolls with a high percentage of hoary-types (like 100%). And at Dan Berard's feeders the large birds seem to show up in waves - none in a group of fifty, and then 8 in a group of 30. What this means for identification is that the birds immediately adjacent to each other are more likely to be similar, and that comparing an "interesting" bird to those immediately around it might not be the best measure of how different the interesting bird is from the "typical". You should try to compare an interesting bird with other redpolls across the entire flock, and don't be surprised if studying one interesting bird reveals the presence of several more.

Update 11 March 2008: I wanted to add two more general cautions suggested by Dan Berard.
1) One of the things that makes size difficult to judge is the fluffiness of redpolls. Birds that are relaxed, with feathers puffed out and sitting more upright, can look larger than adjacent birds that are actively feeding. Be sure to consider what the bird is doing and watch a bird for several minutes if possible to get an accurate impression of size.
2) When redpolls fluff their feathers they reveal more white, making the dark flank streaks relatively less obvious. This is particularly obvious where the upper flank feathers overlap the folded wings, and these feathers can also be displaced and stick out over the wing just after a bird has landed. Dan says his eye is sometimes drawn to a flash of bright white, only to discover that it is not a pale redpoll but simply a redpoll with feathers fluffed or a few feathers askew.

Redpoll investigation widens to include "Greater"

Maybe we are just more aware and looking harder for "Greater" Common Redpolls (Carduelis flammea rostrata) this winter in Massachusetts, or maybe it's really an exceptional winter, but there is no doubt that they have come south in significant numbers. I have seen them on a couple of visits to Dan Berard's feeders in Millbury, MA, where he has been studying redpolls almost daily since December. This has confirmed yet again Yogi Berra's comment that "You can observe a lot by just watching".

This subspecies is relatively poorly-known, nesting on Baffin Island and Greenland and wintering irregularly south to the northeastern US. Literature on identification of this subspecies (Beadle and Henshaw 1996; Herremans 1990, Knox 1988, Pittaway 2007) characterizes it as a consistently large and dark bird. Based on those studies and comments from Dan Berard I've put together a list the features that distinguish rostrata from "Southern" Common Redpoll C. f. flammea, listed in order (my judgment) from most important to least important:

• averaging 10% larger and about 50% heavier
• Generally more heavily streaked below (more streaks and wider streaks); blurry streaks extending along flanks to undertail coverts, which average darker than flammea; at least some individuals are more heavily streaked than any flammea Common. Some have the flank streaks converging into a solid dusky patch at the rear end of the flanks.
• Some in MA (as on most specimens here) have a complete necklace of fine streaks below the dark throat patch, which is very distinctive if present.
• At least some have whole face darker, more streaked, with only faint pale eyebrow stripe, and densely streaked malar. These are probably the same birds with the necklace of streaks, very heavy dark flank streaking, and rich brown color, but even on some of the less obvious individuals a general dusky-headed appearance is evident.
• usually appears longer-tailed
  
• bill may appear thicker with curved culmen
• darker and more richly-colored brown overall
• often looks thick-necked and "front-heavy"
• some have more extensive dark throat patch
  
• male typically has less red on breast and lacks red on malar
• Dan Berard reports that he often hears distinctly different "harsher, more rattling" calls when Greaters are present, although he hasn't yet confirmed that these sounds come from the Greaters.
  

Here's a photo of a flock of redpolls with several large dark birds:

photo copyright Dan Berard, used by permission - click to enlarge. Sharp-eyed readers will notice that the top right bird is quite pale, but unfortunately we can't do much more with that.

Three rostrata "Greater" redpolls are fairly obvious here (blue arrows), being larger and darker than the birds around them. And several others are possibly "Greater" but not quite dark enough or large enough to be identified confidently. Features that seem to be especially useful for picking out these birds are the darker head and broader, blurrier streaking on the flanks than other redpolls, but this is not always consistent. Size is the most consistent feature for identifying this subspecies, but one of the first things you notice when you start looking for larger redpolls in a flock is that size is surprisingly difficult to judge (impossible without direct comparisons) and there seem to be some birds that are intermediate in size. Measurements (e.g. in Herremans 1990, Knox 1988, Knox and Lowther 2000) confirm that rostrata and flammea overlap in all measurements, even though the average is significantly different. So I guess it's not surprising that we would see a full range of size from small to large, and it leaves the question - "when is a bird large enough to qualify as rostrata?"

A side note on psychology and perception - This leads to yet another manifestation of the ambiguity issues that I wrote about previously for White-fronted Geese. Because redpoll identification involves subjective judgment of ambiguous variations in color and size, the first few redpolls you look at can set a standard that persists as you scan the rest of the flock. You can scan a flock once and find a dozen that look like candidates for 'Greater' (or Hoary), then scan the same flock seconds later and find no good candidates!

The other interesting observation about rostrata 'Greater' Redpolls is that they may not be as consistently dark as the literature leads us to believe. Here's a male that is quite pale and grayish, not the heavily-streaked and richly-colored plumage that is considered typical of "Greater". But given that it's an adult male the overall color is within the range of Common Redpoll, and the flank streaking pretty heavy for an adult male.

photo copyright Dan Berard, used by permission - click to enlarge. The bird just behind the "Greater" in the center (facing left) is a possible Hoary, so that should be considered when comparing colors.

Among the large redpolls in Millbury, we've seen a few large birds (non-adult-males) that are paler than the typical flammea Common redpolls (in at least some respects).

Here's a picture of one such bird:

photo copyright David Sibley - 22 Feb 2008. click to enlarge

This bird is one of several seen that day that were obviously large (larger than the goldfinch), and that also stood out among the flock of Commons by their pale overall color, with pale and grayish back and pale head. It also had a pale, but faintly streaked, rump. One thing that still points toward rostrata "Greater" Common is the broad blurry streaks on the flanks, and presumably the undertail coverts were also streaked, so maybe this is within the normal range of variation of rostrata, but the overall paleness is not what I expected.

And here's an even paler bird (I wish I had seen this one in life):

photo copyright Dan Berard, used by permission - click to enlarge

This picture may include three subspecies: rostrata "Greater" on the left, a good candidate for hornemanni Hoary in the middle, and an ordinary flammea Common on the right. The middle bird seems about as large as the rostrata on the left, and larger than the flammea at the right. It's very pale overall, and compared to the pale rostrata-types such as in the previous photo it has a paler nape with less distinct streaks, white flanks with narrow dusky streaks, mostly white undertail coverts, smaller bill, and smaller black throat patch. It's just not quite as white and unstreaked as I expected the "classic" hornemanni to be.

Conventional wisdom holds that rostrata "Greater" Common Redpolls are large and dark, and that hornemanni or "Hornemann's" Hoary Redpoll are equally large and very pale. So I have always assumed that the two would be easier to tell apart than the smaller "Southern" flammea Common and exilipes Hoary Redpolls. But the large birds we've seen in Massachusetts this winter do not all fit the model. At the feeders in Millbury the large birds show a wide range of color variation, from very dark (classic rostrata) to quite pale (but so far none of the very pale classic hornemanni color).

Are rostrata "Greater" Commons more variable than previously thought with some relatively pale individuals? It appears so. But how close can they get to hornemanni Hoaries? And are hornemanni just as variable? Knox (1988) says that female and immature hornemanni can match exilipes in plumage, so can some individuals be relatively dark like the darker Hoaries we've been talking about this winter? Knox (1988) mentions one mixed pair of rostrata and hornemanni from Greenland. He found no other convincing evidence of hybridization, but it is still possible that these two large subspecies are interbreeding, producing a whole range of intermediate plumages. Any or all of these scenarios are possible. The only thing that seems clear is that the plot has thickened, questions abound, and identifying these large redpolls may be more challenging than we thought.

Thanks to Dan Berard for permission to use his photos, for hosting the birds and the birders, and for discussions about redpoll identification.

References:
Beadle, D. and B. Henshaw. 1996. Identification of “Greenland” Common Redpoll Carduelis flammea rostrata . Birders Journal 5: 44–47.

Herremans, M. 1990. Taxonomy and evolution in redpolls Carduelis flammea-hornemanni ; a multivariate study of their biometry. Ardea 78: 441–458.

Knox, A. 1988. The taxonomy of redpolls. Ardea 76: 1–26.

Knox, Alan G. and Peter E. Lowther. 2000. Common Redpoll (Carduelis flammea), 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/bna/species/543

Pittaway, R. 2007. Redpoll Challenge: 4 subspecies. Online http://www.jeaniron.ca/2007/Redpolls/redpolltext3.htm

The Red Knot's troubles

The decline of Red Knots from 1982 to 2006:data from Niles et al. 2007. Status of the Red Knot (Calidris canutus rufa) in the Western Hemisphere. USFWS report.

The Red Knot and Horseshoe Crab story has been in the news in the last several weeks, with a major PBS documentary "Crash: A Tale of Two Species", and the New Jersey Marine Fisheries Council's ludicrous decision to reopen a limited harvest of Horseshoe Crabs in the state (newspaper stories about that can be found in the Press of Atlantic City and the Philadelphia Inquirer).

Now the good news is that the NJ state legislature is considering a ban on Horseshoe Crab harvest, and we should all encourage them to follow through.

Call or write to New Jersey's State Senators before March 10th, as they are considering a ban on Horseshoe Crab harvest in the state (to over-rule the Marine Fisheries Council vote). Visit the NJAS website for details.

Also, in late Feb 2008 nine conservation groups and three US senators signed letters to the Department of Interior urging the emergency listing of Red Knot as an endangered species (details here).

Here is a summary of some key facts:

• numbers of North American Red Knots counted on Delaware Bay surveys have declined from over 100,000 in the early 1980s to only about 14,000 in 2006.
• These knots nest in the arctic, winter in southern South America, and make long non-stop migration flights, stopping in spring primarily at Delaware Bay where they refuel on the eggs of Horseshoe Crabs.
  
• Harvest of Horseshoe Crabs for use as bait in eel traps has led to a drastic decline in spawning crabs (and eggs) on the beaches since the late 1980s.
  
• Migrating Red Knots now have trouble finding enough fuel for their long migration, and (if they reach the breeding grounds) it is thought that most are unable to nest successfully.

It is estimated that the effective breeding population of the eastern North American subspecies of Red Knot Calidris canutus rufa, is now only 1000 to 2000 birds in any given year. These are the numbers that lead researchers to suggest that the subspecies may be extinct within just a few years (from the 2007 Status Assessment available as a .pdf here).

What you can do:

Call or write to New Jersey's State Senators before March 1oth, as they are considering a ban on Horseshoe Crab harvest (to over-rule the Marine Fisheries Council vote). Visit the NJAS website for details.

Support the Delmarva Ornithological Society's Birdathon efforts to raise money to purchase bayfront property as a shorebird sanctuary.

Write to the Governors of New Jersey and Delaware stressing the importance of this natural resource to their states. Delaware needs to enact a ban as well to ensure protection of the Delaware Bay crab population. And hopefully a broader regional plan can be put into place so that the crab harvest pressure is not simply diverted to other states.

Other Resources:
Atlantic States Marine Fisheries Commision

US Fish and Wildlife Service Red Knot info with links to lots of information including the July 2007 Status Assessment (a 16 MB .pdf file, but well worth reading)

New Jersey Division of Fish and Wildlife Red Knot page, also with links to the status assessment and more

The Ecological Research and Development Group, which has been working on alternatives to Horseshoe Crabs as bait

On conserving migratory birds

Taking a break from redpoll identification: I've written an essay about the challenges faced by migrating birds, which appears in this month's Green issue of Delta's Sky magazine. You can read it here.

Where do Hoary Redpolls winter?

In considering the true status and distribution of Hoary Redpoll, I realized that I had overlooked one significant source of information - the Christmas Bird Count results. While Common Redpoll nests throughout the boreal forests across the continent, Hoary is virtually unknown as a breeder east of Hudson Bay (ignoring the "Hornemann's" Hoaries in Greenland and Baffin Island). Therefore the source of virtually all Hoary Redpolls seen in North America in winter must be northwestern Canada and Alaska, and one might expect that Hoary would be less common eastwards in winter. The CBC results show just such a pattern.

Hoary (right) and Common (left) Redpolls recorded on CBCs in two "invasion" years representative of recent CBCs, 1993-94 and 1999-2000.
From National Audubon Society (2002). The Christmas Bird Count Historical Results [Online]. Available http://www.audubon.org/bird/cbc [4 Mar 2008]

There may still be a lot of identification issues with these data, and the coverage in most of Canada and Alaska is spotty or nonexistent, but one pattern seems clear: The proportion of Hoary to Common redpolls is much higher in the west (Alaska, Alberta, and Saskatchewan) and decreases eastwards.