Monday, November 24, 2008

More on identification of Greenland White-fronts

Coincidentally, just days after my last post about the two White-fronted Geese in Concord, two White-fronted Geese showed up in Amherst, Massachusetts (about 60 miles west of Concord, but not the same birds) that appear to be one Greenland and one North American type. James Smith has some discussion and really nice photos on his blog, and he's allowed me to post some of the photos here. 

Two Greater White-fronted Geese - 23 November 2008, Amherst, MA. Photos copyright James P. Smith, used by permission. Click for higher resolution (660 kB). In this montage the upper image shows the apparent North American bird with the Greenland-type on the left. I've resized and pasted in another photo of the Greenland type below for comparison.

This provides a great comparison of the two birds, very well-photographed, in similar light and from similar angles. The Greenland-type bird shows the following differences from the North American-type:
  • neck, head and bill larger and bulkier than the North American-type
  • neck and head more uniform and darker brownish
  • scapulars with slightly narrower and less contrasting pale edges
  • white border on flank feathers narrower
  • pale tips on median and greater coverts narrower and less contrasting, not bright white
  • pale edges on tertials slightly narrower and less white
These are all the same differences that I noticed on the two birds in Concord, and that have been described before as identification features for Greenland White-fronts in Europe. One other feature deserves mention:
  • bill bright orange (and James says the color is accurate and this bird was truly very orange-billed) which may be useful even though we know how unreliable bill color can be, and the other bird happens to be a fairly obviously pink-billed individual, providing a strong contrast. One thing I noticed on the Concord birds, and again here, is that the North American bird has a fairly obvious whitish tip on the bill, while the Greenland bird does not.
And on 24 November, Taylor Yeager posted photos of another apparent Greenland White-front (scroll through the gallery to see several images of this bird), this one in Sharon, MA about 30 miles south of Concord. This bird doesn't look quite as heavy-billed as the other two, but it still looks fairly thick-necked, the bill is bright orange, and it has the dark head, narrow and low-contrast feather edges on the back, virtually no white on the wing coverts, very narrow white flank stripe, and extensive black on the belly between the legs. I'm comfortable calling this a Greenland White-front also. 

This would all seem to lead to confidence in identifying Greenland White-fronts, and I think we're getting there. But when I browse photos of White-fronts from other areas they show a bewildering range of variation. Identifying Greenland White-fronts will require excellent views and a careful assessment of all the different identifying features, preferably with direct comparison to other White-fronts, and a healthy dose of caution.

Another photo of the two birds in Amherst: Greenland-type in front showing the much larger and bulkier bill and head, and thicker neck, in comparison with the more delicate features of the North American-type bird behind. Photo by James P. Smith, used by permission. 23 November 2008, Amherst, MA.

Finally, one further mystery: It's not at all clear how we can tell that the smaller bird in Amherst is a North American White-front rather than a Eurasian bird. I don't think I've ever seen a discussion of that identification issue, but Eurasian White-fronts show up rarely in Iceland, and could easily wander into North America from there or from Siberia, so it is a potential vagrant to North America. All I can dig up in a cursory search is that Eurasian birds are consistently pink-billed, and may average smaller-billed, and may average less white on the wing covert and tertial edges, but those things are all vague, subjective, and variable. So while I've called the smaller bird in James Smith's photos a North American-type, I can't actually rule out the possibility that it is a Eurasian bird. Any comments or suggestions welcome. 

Friday, November 21, 2008

Identification tips for Greenland Greater White-fronted Goose

The Greenland Greater White-fronted Goose (Anser frontalis flavirostris) is known to be a rare visitor to northeastern North America, but I have never been satisfied with a reliable, objective way of distinguishing it from the North American subspecies of Greater White-fronted Goose, also a rare visitor to the northeast.

Bill color is the most frequently-mentioned field mark – supposedly orange on Greenland birds and pinkish on North American – but this has been refuted multiple times (see Kenn Kaufmann's note in Birding 1994, my blog post here). I suspect this is a mark that works in Europe, where local White-fronts are reliably pink-billed, but not in North America, where lots of the local birds look more or less orange-billed.

Over the last few weeks a single adult White-fronted Goose has been frequenting farm fields near my home in Concord, Massachusetts, and about a week ago it was joined by a second bird (well... "joined" is an overstatement since they pay no attention to each other and keep apart in the big flock of Canada Geese). 

These two individuals, in their details, are really strikingly different, and the differences all lead me to the conclusion that the new arrival is a Greenland bird, and the other a North American bird. On 19 November I was able to get some photos of the Greenland-type bird, and I've annotated a photo here with the differences between it and the North American-type bird. The differences are listed simply from front to rear, not in order of importance. (I'll try to get some photos of the other bird to post here for comparison).

Presumed Greenland Greater White-fronted Goose, 19 November 2008, Concord, MA. Photo by David Sibley
  1. bill color slightly more orange, with yellow base (vs. orange with pale pink base on the other bird); but this is very very difficult to judge and essentially worthless as a field mark (see my post from last fall about judging bill color).
  2. whole head nearly uniform dark brownish, sometimes looking paler on the cheeks but still with solidly dark crown above the eyes (vs. paler gray-brown head and neck with narrow dark crown stripe and contrasting dark border along white front). This is highly dependent on lighting, and would be difficult to judge on a lone bird, but the Greenland-type bird does look consistently darker, and may show a contrasting dark hind-neck that the other bird doesn't, but I need to check that in more lighting conditions.
  3. neck strikingly thick and heavy, no thinner than the head (vs. neck slender, obviously narrower than the head and looking graceful and slim). This is one of the most obvious differences on these two individuals.
  4. margins of mantle and scapular feathers pale brownish, not strongly contrasting (vs. margins whitish, more strongly contrasting).
  5. white border on flank feathers narrower and not extending as far forward (vs. broader and longer)
  6. pale tips on median coverts narrow and not white, relatively inconspicuous (vs. broader, whitish, conspicuous)
  7. greater coverts without pale edges, and with narrow and inconspicuous whitish tips (vs. obvious narrow white edges and broad white tips forming a conspicuous narrow white band across edge of folded wing). This is another obvious difference between these two individuals.
  8. black smudges all over the small feathers of the belly between the legs and extending well behind the legs (vs. this area virtually all white). This is separate from the irregular black bands before the legs and up onto the flanks, which are marked similarly in both birds.
  9. white tips on the tail feathers seem to be narrower on the Greenland-type, but this is very difficult to see in the field.
Overall the Greenland-type bird appears bulkier, heavy-billed and thick-necked, and darker, without the elegant white fringes that are prominent on the rear upperparts of the North American-type.
Here's another photo of the Greenland-type bird, showing the heavy orange bill, dark and thick neck, and the lack of contrasting edges on the feathers across the shoulders. But none of that is very helpful in a single photo without another bird for comparison, nor is it likely to be very helpful on a single bird in the field. 

I know that some of these things have been described before, and they are still pretty subjective, and it's not safe to generalize from a single individual, but if this is a typical Greenland White-front, then I feel more hopeful about identifying the subspecies.

notes:
Martin Reid's website has some other discussion, photos, and lots references

Wednesday, November 19, 2008

Sungrebe – New for North America!

Stunning news from Bosque del Apache NWR in New Mexico: a female Sungrebe was photographed there on 13 November 2008, those photos here. It was correctly identified on 17 November from the photos, then refound and photographed more on 18 November. This is not only a new species for North America, but a whole new family.

A map of the species' whole range can be seen here at InfoNatura (scroll down for the detailed map).

Of course, birders are already debating whether this is a wild, naturally-occcurring bird or an escape from captivity. On one hand, it's a secretive species that is rarely seen flying, with no known history of vagrancy or even real seasonal movements, making the prospect of one appearing nearly 1000 miles northwest of the closest known population seem very unlikely. On the other hand, it's not kept in any zoos, and doesn't seem like the kind of species that would be illegally transported by an individual, which makes the escapee theory unlikely also.

Tipping the balance in favor of natural occurrence, in my opinion, is that in South America Sungrebes are apparently quick to occupy ephemeral wetlands, even when those are isolated many miles from any other suitable Sungrebe habitat. So clearly they are capable of long-distance flight, and wander enough to discover recently-created habitat. Perhaps, like rails, or Masked Ducks, they are capable of amazing feats of vagrancy.

Unless there is some clear evidence of captivity, I would consider this a wild bird. Incredible!

Update 19 November: Jerry Oldenettel has more details and will be updating the bird's status on his website here; and apparently the original photos were taken 13 November, and identified on the 17th, so the bird has been present at least six days.

Monday, November 17, 2008

Lesser Canada Goose in the northeastern US

The primary challenge of distinguishing Canada from Cackling Goose centers on the intermediate-sized 'Lesser' Canada Goose, B. c. parvipes, which reportedly nests across the boreal forest regions of western Canada and interior Alaska (more details on my website here). I've seen a few birds that I thought were 'Lesser' in the northeast over the years, most convincingly one at Brigantine NWR in NJ that accompanied a big flock of Snow Geese rather than flocking with Canadas. But it's a pretty ambiguous subspecies. The identifying features are wholly subjective: anything that seems smaller than the regular Canadas but too big for Cackling is a candidate for 'Lesser' Canada. Recently I saw this bird (the one on the left) that I feel pretty confident is a 'Lesser':
click for a slightly larger image. 
16 November 2008, Great Meadows NWR, Concord, MA - photo by David Sibley. Taken with the 10x zoom on a Canon digital camera. The Canada on the right was a bit farther to the right in the original photo, I cut and pasted it closer for better comparison.

It was distinctly smaller than the Canadas around it, with a very short neck and short bill. In flight going away it appeared no more than 2/3 the bulk of the Canadas next to it. Whenever I scan Canada Goose flocks in the east looking for Cackling Goose, there are always a few birds that grab my attention because they look small. Often they are marginally smaller than the other Canadas, sometimes their smallness was an illusion (happened to be standing in a furrow, next to an unusually large goose, etc). After a closer study these "small" birds fit nicely into the normal range of variation of the local Canadas, and the impression of smallness vanishes. This bird stood out because its smallness held up to closer scrutiny; it was truly small with very short neck and short bill.

I called it a Canada rather than Cackling because it seemed just a little too long-billed, too large overall, and the head/bill too wedge-shaped for 'Richardson's' Cackling Goose. It also looked the same color as the Canadas around it, without the gray sheen on the back or golden cast on the breast that many 'Richardson's' show. 

There are very few reports of 'Lesser' Canada Goose in the northeast. This could be due to the difficulty and inherent uncertainty of identification: we identify only the most clear-cut examples and report those tentatively, if at all. Or maybe it's because few birders really look for them or follow-up on possibles since "it's just a Canada Goose". Or maybe they are truly rare. I have actually seen more 'Richardson's' Cackling Geese in the northeast than convincing 'Lesser' Canadas; but that could be due to any of the reasons above. Given the normal distribution of this subspecies – breeding farther south and west than 'Richardson's' Cackling, with shorter migration – I would expect it to be less frequent than 'Richardson's' on the Atlantic coast, at least in the north. The only way to figure that out is to keep watching for, and documenting, these small geese, in order to develop a better sense of the identification and status of the various subspecies.

Saturday, November 15, 2008

How many rare birds did we miss before the internet?

Yesterday morning I 'found' Canada's first Lucy's Warbler... in my inbox. 

After reading my recent posts about rare birds, Cathy Mountain (whose redpoll photos were featured here last winter) sent me a series of pictures of a warbler that had been in her yard in Fort McMurray, northern Alberta, from November 8-10, 2008. 

After rejecting the possibility of a drab Yellow Warbler, she thought it might be a Virginia's or Lucy's Warbler, as did other local birders who saw the photos, but they were reluctant to call it since both of those species were so unlikely. 

photo by Cathy Mountain - used by permission

This photo is not the sharpest in the series, but it is the best for showing the identifying features: the small pointed bill, plain gray color, pale lores and eyering, and dark rusty rump just showing under the wings. (and Yes, that is snow.)

This highlights another line of evidence in the debate about how many rare birds we miss - the number of rare birds found and identified only because they are photographed. This bird, like West Virginia's Great Knot in August 2007, and countless others, would have been lost in the swirl of ambiguous possibilities if not for photography. And without the internet to allow immediate sharing, even photos might have laid in a drawer with a very low chance of ever being identified. 

Imagine the chain of events that led to this discovery:
  • In all of northern Alberta, this warbler landed in the yard of a birder (maybe not entirely random since Cathy probably has some landscaping to attract birds, but still... northern Alberta's a big place)
  • She had to notice it and take some pictures
  • She had to realize it could be something noteworthy and go to the effort and the risk of showing the photos to other birders to try to identify it
  • When it remained a mystery she had to continue pushing the pictures out on the internet
Judging from her email to me, I think she knew what it was, and just didn't have the confidence to say, but did have the confidence to keep trying to confirm her suspicions.

Now imagine if any one of the links in this chain had broken down. The bird didn't land in a birder's yard, didn't stay long enough or simply wasn't noticed, wasn't photographed, or wasn't 'advocated for'. This Lucy's Warbler could have landed unnoticed in dozens of yards on its trip from Mexico to Alberta. 

The digital photography revolution, and the ability to share pictures easily on the internet, means that a lot more of these birds are found (meaning confirmed), which is fantastic. But this still must be a fraction of all the rare birds that are out there.

So get out there and find something!

Thursday, November 6, 2008

So how many do we find?

My last post "How many rare birds do we miss?", was simply getting at the idea that we can miss something glaringly obvious if we are not looking for it. A popular psychology quote goes "I wouldn't have seen it if I hadn't believed it". In the case of the moon-walking bear, since I wasn't looking for it, I didn't see it. 

In the comments a reader pointed to a discussion on his own blog "The Birdist" where he actually tries to answer the rhetorical question in the title of my blog post. So how many rare birds do we actually miss? The Birdist and his interviewee guess that one-third to over one-half of all rare birds are found. I disagree and I would put the percentage much much lower. 

Why do I think so few rare birds are found? Well, for one thing, I look at the very small number that are ever refound. The White-crested Elaenia in Texas last January, or the Variegated Flycatcher in Washington this September, or the European Golden-Plover in Maine in October, or the White Wagtail in the Florida Keys last week, etc etc. all share the fact that none of them was seen anywhere else in North America. Maybe a statistician can comment on the hypothetical numbers involved, but if one-half of all rare birds were being found by birders, I would expect a lot of re-finding of these ultra-rarities. It's likely each of these birds wandered slowly and spent time at many other places where they could have been discovered by birders, both before and after their actual discovery. And there must be countless others that are never found. 

The Jabiru in Louisiana July 31, 2008 could be the same one that was seen in southern Texas August 10th and 20th. But that is a big, conspicuous species that even a non-birder will notice. In fact, as I understand it, it was found in Louisiana by a local hunter who noticed it and took a few snapshots. It was refound by a birder in Texas on August 10th (if indeed the same bird) but then went missing for 10 days, reappearing on August 20th! Add to that the experience in August 2007 when a Jabiru showed up in Mississippi. Birders were alerted to it by the local farmers, but after a few days that bird vanished and was never seen again, despite intensive searching and the fact that its most likely path back to Central America would have taken it through Louisiana, past Houston and Corpus Christi, and over several hawkwatches. Rare birds being refound at a distant location are the very rare exception to the rule. 

Another interesting bit of evidence is what I will call "delayed discovery". There are many examples, as in the 2007 Mississippi Jabiru that was seen by birders only because the landowner was curious and sent out a photo. It turns out the bird may have been in the area for several weeks before that. Or the Least Grebes recently discovered in a park in Boca Raton, Florida. On September 27th self-described "recreational birders" Lee and David Hasse sent an email alerting other birders that "last Sunday" they saw two Least Grebes. This was confirmed by their photos and by "serious birders" the next day. The following day (28th of September) the nest was discovered, and on the next day (29th) the first egg hatched!

The eggs must have been laid about 3 weeks before they hatched, and nest-construction must have started at least a week before that, and probably several weeks for pair formation, etc. So those two grebes must have been at that park for at least 6 weeks, since mid-August. And if the Hasse's weren't there in late September, or hadn't taken the time to report their sighting, would the entire nesting have passed without birders noticing?

So I'll take on the question now: How many rare birds are actually found? At a place like Cape May in the fall, arguably THE most intensively birded location in North America, a Jabiru is almost certain to be seen and identified, I'd say 80 or 90% of the time, and if it sticks around for more than an hour or two the odds go up to near 100%. As we go down the scale of conspicuousness, Fork-tailed Flycatcher is fairly likely to be found (virtually all birders and even a lot of nonbirders would notice one, even from a great distance); Western Tanager is less likely to be found (much less conspicuous - you have to be within a few hundred feet to notice one); Smith's Longspur is even less likely (secretive and nondescript), etc. The odds of finding a Smith's Longspur that only stays for a day are very very low overall (although if it spends that day on the lawn by the Cape May hawkwatch, it's very likely to be found). Staying longer will increase the chances of being found, and so on.

Psychologically, birders at places like Cape May are somewhat more likely to find rare birds simply because, at known vagrant traps, we expect to find rare birds. The same observation that might set a Cape May birder running after a "possible Smith's Longspur" is more likely to be dismissed as "not worth the effort" by a birder in farm fields in upstate New York. And as soon as a historical pattern develops at a location - like Cave Swallows at Cape May in November - the tables turn and birders start actively looking for a specific rare bird.

Back to my point about birds not being refound: if each of these rarities is spending 10 or 20 or 30 days wandering around inside North America, but is only seen once, that's something like a 10% or 5% or 3% chance of being found, and that strikes me as the right range to consider for how many rare birds we actually see.

As a final note, I like to think that this makes me an optimist, since I can always convince myself that the European Golden Plover from Maine is going to show up in my local patch tomorrow, and that there must be loads of rare birds hiding in the next bush.


Tuesday, October 21, 2008

How many rare birds do we miss?

As birders we often talk about the problem of common birds being misidentified as rare ones. The counterpoint, but probably more frequent, is that rare birds are simply overlooked. Here's a link to a fantastic "Awareness Test" on YouTube. 

Give it a try, it only takes a minute. The relevance of this test to bird identification should be obvious, so now you can just imagine all the rare birds you haven't seen.

Tuesday, May 6, 2008

Big Day, and Blogging hiatus

Upcoming events: I'll be out on a fossil-fuel-free big day this coming weekend, bicycling around Concord, Massachusetts (hoping for 100 species) and I'll try to post a report about that next week. You can sponsor me through Bird Studies Canada, or through Malkolm Boothroyd's Bird Day Challenge.

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The Blog: When I started this blog last August I didn't have much of a plan, or much time, but it has evolved and grown, and the whole experience has been great. Thanks to all who have contributed, publicly and privately. For the last month or so I've had no time to work on it at all, and I expect to be equally busy for the next few months. If I find time I will post occasionally, but I look forward to having more time for it, hopefully by the end of the summer. In the meantime, why not go outside and watch some birds?

Thursday, April 10, 2008

More on Texas Border Wall

Prompted by some good discussion I've read on TexBirds and elsewhere: I want to stress the point that the danger to birds is not so much the height of the wall, but more the wide swath of habitat that would be cleared for the wall and service roads. Chachalacas, Pygmy Owls, Green Jays, etc will fly over a wall, but they're less likely to cross 100 yards of barren gravel. This project might as well be a 4-lane highway.

So let's try to take immigration completely out of the picture for a moment and imagine that, instead of a wall, the federal government was proposing to build a 4-lane expressway along the river from Brownsville to Laredo. Wouldn't there be a unified grassroots uprising against it? What if they revealed that it would cut right through parts of the LRGV Wildlife Corridor, which has been so carefully patched together and cultivated over the last 20+ years? And what if there would be no exit or overpass anywhere near the Sabal Palm sanctuary and other sites, effectively cutting those places off from the existing road system? And, on top of all that, what if they announced that, in order to speed construction, all environmental review would be waived? Wouldn't we all be outraged?

People may feel conflicted or uncommitted about the border wall because it is tangled up in hot-button issues of immigration and National Security. But those issues are irrelevant to the birds. The reality is that the wall (like an expressway) would be catastrophic for birds and birding in the valley (and what's bad for birding is generally bad for the birds), and we need to speak out to demand that those concerns be addressed. Congress allowed all this to happen, and they can change it, but they need to hear from lots of us. See http://noborderwall-take-action.blogspot.com/

Monday, April 7, 2008

Border Fence puts Texas birds and birding at risk

Revised 8 Apr 2008 -
Do something: Write or call Congress. See the No Texas Border Wall campaign and their suggestions for action with several petitions to sign and instructions for contacting government officials. Defenders of Wildlife has a handy form here for writing to your representative.
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The proposed border wall (1) from Texas to California has been hotly debated, but birders should be aware that aside from local residents (2), as a group, we will be among those most strongly affected by it. Problems include:
  • the destruction and fragmentation of habitat - imagine building a four-lane highway through the area (3).
  • current plans call for the wall to be erected between US birders and several of our most popular birding sites - such as the National Audubon Society's Sabal Palm Grove, The Nature Conservancy's Southmost Preserve, and parts of the Lower Rio Grande Valley National Wildlife Refuge - relegating those places to the Mexican side of the fence, with no plans for visitor access (4)
  • over 30 environmental laws were summarily waived on 1 Apr 2008 (no joke), so that construction of hundreds of miles of border fence would not be slowed down by the nuisance of considering endangered species, clean water, Native American burial sites, etc. (5)
Border security is important, but for whatever help this wall will provide (6), the need for secure borders should not trample environmental laws. We must be able to increase security while still maintaining the natural and cultural heritage of the border region.
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Notes:
1) In the subtleties of language, calling this a fence implies a neighborly sort of boundary marker. It is really a wall, actually two walls - at least 15 feet high, solid metal and concrete, with a road on either side (see photos here).

2) Local residents are overwhelmingly opposed to the wall. An article in the Texas Observer with the local viewpoint and other issues is here

(3) from a Houston Chronicle article here "Federal wildlife officials said they are concerned the waiver of the Endangered Species Act and other environmental laws will threaten the survival of a number of animals by allowing the fence to be built through a 90,000-acre wildlife corridor they spent $100 million assembling in South Texas."

(4) A refuge official says that over two-thirds of National Wildlife refuge land in the Valley will be negatively impacted, either directly or indirectly. Not to mention that access to the river will be limited, and a number of homes, businesses, and historic sites will be on the other side of the planned wall.

(5) Defenders of Wildlife press release here

(6) only 70 miles of wall are planned along 300 miles of the Rio Grande. Eagle Pass Mayor Chad Foster told the Houston Chronicle here "I'm just a yahoo from Eagle Pass, Texas, but this is just the absolute height of folly"

More info:
8 Apr New York Times story about the legal issues of the waiver is here
A detailed 4 Apr story in Newsweek is here
The 7 Apr New York Times story about the issue here
A Houston Chronicle story is here

Defenders of Wildlife press release here and lots more in the "Related Information" sidebar

Wednesday, April 2, 2008

Variation in Wild Turkey

Here's an example of one of the countless thousands of questions that are still out there waiting to be answered about North American birds. I went to Texas in February (for the opening of the fantastic new Clif Moss Nature Education Center of the Corpus Christi Public Library) and I had a chance to see some Wild Turkeys nearby. As expected they had whiter tips on all the body feathers than northeastern birds, but they also seemed thinner and smaller-headed than the Turkeys that frequent my backyard in Massachusetts, and when I got home I immediately saw what the difference was.

sketch copyright 2008 - David Sibley

The Massachusetts Wild Turkeys have feathering extending all the way up the neck, while the Texas Turkeys have a long stretch of the upper neck bare (here's a quick sketch I did that first morning at home). This is logical, presumably an adaptation to the cold weather in Massachusetts, but in a quick review of some sources (the BNA account) I found no mention of neck feathering as a geographic difference. I thought maybe it was just a winter feature; maybe the Texas birds had already lost their "winter coat", and the Massachusetts birds would lose their neck feathers for the summer. They may still do that, but as of today (2 April 2008) they look the same.

As usual, this just brings up more questions: Is this going to be true year-round? What are the patterns of variation? Do all southern birds - Florida, Texas, Arizona - lack neck feathers? Does it change gradually from north to south or is the change more abrupt? and lots more....

Friday, March 28, 2008

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.

Wednesday, March 26, 2008

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.

Tuesday, March 11, 2008

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.

Monday, March 10, 2008

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.

Friday, March 7, 2008

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

Wednesday, March 5, 2008

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

Monday, March 3, 2008

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.

Tuesday, February 19, 2008

House Sparrow - "New" for North America?

[Major updates 25 Feb 2008, adding new information about the introduced Siberian populations]

You might think that the words "intriguing" and "House Sparrow sightings" are mutually exclusive, but here's a case where they go together! In October 2007 a flock of five House Sparrows showed up in the coastal village of Shishmaref in northwest Alaska. They were found and photographed by science teacher Ken Stenek, as you can read on his website here. Two males were still present as of mid-Feb 2008, demonstrating how hardy this species can be.

House Sparrow is a very rare visitor anywhere in Alaska, with only a few records in the state. Interestingly, one of the few prior Alaska records comes from Gambell, on St Lawrence Island, in mid-summer about 15 years ago. So the question is whether these birds, at the very western edge of Alaska, came from North America or Asia. North American birds originate from multiple introductions in the eastern states in the 1800s. They spread rapidly but they have not spread beyond southern NWT. In fact, in recent decades the species has been declining across most of its world range.

In contrast to the widespread declines in the developed world, House Sparrows have been expanding their range in East Asia, although this expansion is apparently man-made, involving deliberate transplants and releases of House Sparrows in Siberian cities (fide Dan Gibson). The spread of House Sparrows across North America was "accelerated" in the same way a century ago, and the success of the birds must also depend on development and human land-use changes and possibly also warming climate in recent decades. They are now apparently established in a number of settlements along the Russian coast of the Bering Sea at least as far east as Anadyr (Paul Lehman, Dan Gibson), and it would be very interesting to know whether or not these populations are increasing.

Above is an updated map (25 Feb 2008) of the current range of House Sparrow around Alaska (comments welcome). Shishmaref is indicated by the large red dot. Smaller red dots show Ketchikan in southeast Alaska where there have been five records of House Sparrow, two of those records involve pairs (fide Steve Heinl), and Gambell, on Saint Lawrence Island, where a single House Sparrow was found in summer 1993. Purple dots in Siberia show cities where House Sparrows are known to have been introduced - Magadan, Kamchatskiy, Anadyr, and Providenya (fide Dan Gibson), and presumably they have also been released in other cities and towns.

In North America the nearest population of House Sparrows is in southern NWT, about 1500 miles east-southeast of Shishmaref. In Asia the species occurs "naturally" only as close as the west edge of the Sea of Okhotsk, about 2000 miles west-southwest. Introduced populations are found along the coast farther east, including Anadyr, less than 500 miles west of Shishmaref, and Providenya, less than 100 miles from Gambell, where some were apparently released just weeks before the 1993 record at Gambell (fide Dan Gibson). My earlier assumption that these cities had been colonized naturally is apparently incorrect, and I don't know how healthy those populations are, whether they are increasing or not, or whether any persist in Providenya.

Still, the fact that Asian populations are so much closer argues in favor of an Asian origin for the Shishmaref birds. The water crossing, on the other hand, seems formidable for birds coming from that direction, and makes many people think the birds must have been "assisted" in their trip to Shishmaref.

If House Sparrows were coming to western Alaska from Canada I would expect them to colonize Fairbanks and other interior Alaska cities along the way. (They have not). Maybe these birds came up on a boat, especially given increased shipping traffic with the longer ice-free summers in recent years. If any bird has a chance of being transported by truck, train, or ship, it is the House Sparrow. But then I would expect them to be seen in Juneau, Haines, Anchorage, Fairbanks..., all cities with bustling transportation centers. Why Shishmaref?

The answer to the question of origin could possibly be found in a careful study of the birds' plumage, since North American birds must look slightly different from Asian birds, although all involve the nominate subspecies P. d. domesticus. Or perhaps stable isotope analysis of feathers could reveal the birds' origin. Ultimately, the next decade or so will probably give us the answer. If House Sparrows are increasing in eastern Siberia and begin to colonize other western Alaska towns (without appearing in southern Alaska) that will be strong evidence that they are invading from the west.

For now it's a very intriguing House Sparrow sighting, potentially adding a new species to the list of naturally-occurring birds in North America.

Notes:


details of North American distribution from Audubon Christmas Bird Count data

Anderson, T. R. 2006. Biology of the Ubiquitous House Sparrow: from Genes to Populations. Oxford Univ. Press. available online here

Wednesday, February 13, 2008

Redpoll age variation and ID

The question of age variation has come up repeatedly in redpoll discussions, so I finally tried to find an answer to the question of just how important age-related variation in plumage might be. And based on published studies the answer is ... not very important.

Seutin et al. (1992) studied redpolls at Churchill, Manitoba using a character index, and found only one statistically significant age-related plumage difference (aside from the obvious red/pink breast of adult males) - flank streaking on adult males was lighter than on any other age/sex class. All other features - undertail covert streaking, rump color, forehead color, poll color, etc. were statistically the same on adult male, immature male, adult female, and immature female. This near-complete absence of age-related variation differs from what Knox (1988) reported - that in European redpolls immatures are darker than adults. I haven't read the Knox paper, so I don't know how different the results actually are, but regardless of what he found in Europe, the paleness of a redpoll in North America does not seem to be linked to the bird's age, and therefore ageing a redpoll is not helpful to the identification process.

The lack of age-related variation does make sense given the lack of differentiation in redpolls at all. Going back to the species question: Seutin et al. analyzed their data on plumage variation by searching each age/sex class for any sign that the distribution of scores was bimodal; e.g., did each age/sex class show any hint of sorting into paler and darker groups on any of the measured plumage characters? Only adult males showed a tendency to sort into two groups, and that was slight. Immature males showed a suggestion of sorting into pale and dark groups only when sophisticated statistical tests were applied to the data. Attempts to sort females of either age class into pale and dark groups failed completely.

Combining this with Troy's similar finding that redpolls form a continuum from pale to dark, and Troy's data showing that intermediate-colored birds were also intermediate in skeletal measurements, implies that observers should expect to find lots of intermediate birds that cannot be confidently assigned to a species.

It's possible that characteristics not measured by Seutin or Troy - like scapular color, or forehead fluffiness, or voice, or something else (?) - might lead to better separation of two groups, but their inability to distinguish two clear groups does not bode well for identification of non-adult-male redpolls.

Monday, February 11, 2008

White-crested Elaenia - new for North America

[edited 12 Feb 2008]
From Texas comes the remarkable news of the discovery of an apparent White-crested Elaenia (Elaenia albiceps) found by Dan and Honey Jones on 9 Feb 2008. Photos, sound recordings, and ID discussion can be found at Martin Reid's website and some great photos at Erik Breden's website. The bird was found at the Sheepshead Woodlot sanctuary (preserved by the Valley Land Fund) on South Padre Island. [Update: after being seen by many on 10 Feb, the bird could not be found on 11 Feb; hopefully it will reappear]

Given that South Padre Island is a barrier island on the Gulf of Mexico, just north of the Mexican border, it has a distinct geographic advantage when it comes to attracting rare birds. But this particular species could have turned up almost anywhere. The fact that it landed just across the Mexican border would seem to be just a fluke (although one can't discount observer effects: birders on the Mexican border tend to be a little more open to these possibilities when an "odd" bird is found). White-crested Elaenia is a South American species, nesting in Chile and Argentina during the southern summer and migrating north to winter (during the southern winter) in the Amazon lowlands. [update: to clarify, this is referring only to the migratory southern "Chilean" subspecies, which may be a different species from the more or less sedentary populations in the Andes farther north. I'm assuming that the Texas bird is from the migratory southern population.] Fork-tailed Flycatcher is another austral migrant, and a more familiar vagrant in the US and Canada.

So let's speculate about some dates: If this is a young bird it most likely fledged sometime around January 2007, about one year ago. Then in April it migrated north to the lowlands of Brazil, where it stayed for the few months of the southern winter. In October 2007 it would have been ready to migrate back to its breeding range in southern South America, and presumably at that point it made a mistake and migrated north instead of south, bringing it to North America. Right now it should be on its breeding grounds, in mid to late summer. The urge to migrate should have waned in December, but maybe this bird found itself in some inhospitably cold place and was forced to move south for food, bringing it to South Padre Island. Or maybe it's been in that area since last fall. Or maybe this bird's clock, along with its navigation system, is screwed up and it's just off on a wild adventure. We'll never know, but given that the species has a range and migratory pattern like Fork-tailed Flycatcher [wrong - see note below], it is plausible that its patterns of vagrancy would be similar, and that suggests the scenario that this individual arrived in North America about three months ago.

The breeding range of this species is centered about 5000 miles (in a straight line) from South Padre Island, which is a remarkable distance. Small changes in direction of flight, or distance, would bring the bird to very different locations. It could just as easily have turned up at any of the Gulf Coast barrier islands, or a desert oasis like Big Bend, and traveling just 20% farther would bring most of the eastern US within its range! Something to watch for....

Note: Thanks to Chris Vogel for pointing out some flaws in my speculation, which reveals my ignorance of South American birds (and a lack of research). The range and migratory patterns of White-crested Elaenia and Fork-tailed Flycatcher are not very similar after all. Here are maps from Natureserve's InfoNatura database showing the ranges - Fork-tailed Flycatcher (left) and White-crested Elaenia (right)

both images © 2007 NatureServe, 1101 Wilson Boulevard, 15th Floor, Arlington Virginia 22209, U.S.A. All Rights Reserved.

White-crested Elaenia nests in the highlands of western South America, Fork-tailed Flycatcher in the lowlands of eastern South America. There is little overlap in breeding range and the migratory patterns must be quite different. Chris stresses the fact that altitudinal movements are a significant part of the Elaenia's migration, from colder mountains to warmer lowlands, while Fork-tailed Flycatcher is a lowland bird all year. Anyway, the main point I was trying to make is that both species are long-distance austral migrants (at least partly) and the Elaenia (like Fork-tailed Flycatcher) could have turned up almost anywhere in North America as easily as at South Padre Island.

Thursday, January 31, 2008

Upcoming events in early 2008

Feb 24 - I'll be speaking at the Northwest Branch of the Corpus Christi Public Library on February 24th at 4 PM to help celebrate the opening of their new Clif Moss Nature Education Center. Some details here. And if you're in the area that weekend check out the Celebration of Whooping Cranes in nearby Port Aransas.

March 21 - I'll be in Irvine, CA for the Annual Dinner of the Sea and Sage Audubon Society, and on the following morning I'll be presenting a workshop on drawing birds. Details here.

March 29 - I'll be among a group of authors at the Newton, MA Public Library for their "Spring Fling" Here's the blurb from the Library's website:
It’s not too early to dream of spring, so mark your calendars for the Newton Free Library’s annual Spring Fling gala event, Saturday, March 29, 2008, 7:00 pm, at the library. This library lovers’ evening will honor regional authors including co-authors Jody Adams and Ken Rivard, Joseph Finder, Rebecca Goldstein, Nathaniel Philbrick, Rishi Reddi, and David Allen Sibley. Enjoy conversations with the authors, a literary-themed silent auction, excellent food, and good music. You will have the opportunity to purchase the honorees’ books and have them personally signed by the author. Tickets go on sale in February. For more info, contact Devra Kiel Simon, Director of Development, 617-796-1407 or dsimon@minlib.net.
May - I'll be participating in a Fossil-Fuel-Free birdathon supporting Malkolm Bothroyd's Bird Year as part of the Bird Day Challenge, which you can read about here. And I'll also be participating in BirdStudies Canada's Baillie Birdathon. I will fill in more details on these events later. If you'd like to sponsor me in either of these efforts please use the links above for info.

Monday, January 14, 2008

Urging caution when identifying Common Redpolls

Redpoll identification is challenging because Hoary and Common Redpoll seem to show an unbroken continuum of variation from pale to dark, and there are no fully reliable differences. So birders have to rely on a subjective assessment of overall color and struggle to define the threshold for confident identification. Virtually all birders see redpolls only in the winter, where identification is reduced to an utterly one-sided question: "Where can we draw the line so that we are sure the accepted records of Hoary Redpolls are correct?"

Since the goal is high confidence, this leads to a narrow definition of Hoary Redpoll - only the palest (and smallest-billed) birds are named and reported as Hoaries. This leads to two problems (the second more serious). First, we only identify part of the population - some darker Hoary Redpolls are excluded. Second, many of those intermediate birds are simply lumped into our broad definition of Common, and receive no extra attention. There's nothing wrong with excluding some intermediate birds from being called Hoaries, as long as birders understand that some Hoaries are being excluded. This is conservative. But most people give redpolls very uneven treatment by demanding that Hoaries meet high standards, and then calling everything else Common. This is not conservative. We should at least be fair and apply equally strict criteria to our Common Redpoll identifications.

By excluding some darker Hoary Redpolls (and calling them Commons) this uneven treatment prevents us from understanding Hoary Redpoll as a population.

Some might argue that this approach is correct, but it is not supported by Troy's (1985) research. Troy found that all redpolls breeding in taiga/forest habitat were uniformly in the darkest one-third of all redpolls he studied (with no intermediates at taiga sites). Redpolls breeding at tundra sites, on the other hand, were primarily in the paler two-thirds (from intermediate to very pale). If we start with the hypothesis that Common Redpoll is a dark southern population with its core nesting range in the forest and Hoary is a paler tundra-breeding population, then the intermediates, which Troy found only in the tundra habitats, seem most likely to be either hybrids or darker variants of Hoary. Calling these intermediate birds Commons would imply that Common Redpoll is represented by dark birds in the taiga and paler birds in the tundra. This seems less parsimonious and, if true, suggests that we should consider the possibility of two subspecies of Common Redpoll along those lines. I don't know of any research that would help resolve the status of these intermediate birds.

So we need two different approaches to identification. The traditional conservative approach is fine if we acknowledge its limits and we are just trying to be confident about adding Hoary Redpoll to a list. But if we are trying to understand Hoary Redpoll as a species, we need a more inclusive definition that will identify the whole population. In the short term, I think we need to use the "intermediate" label more, calling lots of birds "intermediate" until we get a better understanding of where to draw the line.

I realize that the birds in my redpoll photos are outside of the traditional "safe" zone for Hoary Redpoll, but it's misleading and obscuring to say that these birds are just "pale Commons". I am convinced that the birds I photographed are not just Commons and they presumably come from tundra habitats where Hoary nests. Whether they are good Hoaries or hybrids/intergrades is the next question. But we can't even begin to answer that question if we just dismiss them as non-Hoaries. We need to spend more time studying these intermediate birds, and resist the urge to stick arbitrary labels on them, if we are to have any chance of answering the bigger questions about redpolls.

Notes:
1) Matt Sharp suggested that the differences between two of the redpolls I photographed and called Hoary-type and Common, are simply age-related. I have very little experience judging tail feather shape so I don't want to attempt ageing, but if there is a difference between these two birds I would reach the opposite conclusion to Matt: it looks to me like the paler bird has more pointed outer tail feathers than the darker bird and is therefore more likely to be a 1st-winter, ... but I'll defer to banders' opinions on feather shape!

Regardless of feather shape, I can't accept that age alone explains the plumage differences. This pale bird was one of two or three similar individuals among 75 to several-hundred Redpolls I saw that day. These pale birds stood out subtly but distinctly from the darker brownish Commons. There was certainly a range of variation in color among the Common Redpolls, but these few birds still stood apart. They were paler overall than any female-type Common, with a "colder" gray tone, had slightly finer and paler streaking on the flanks (index score 3+), mostly white rumps with just a few dusky marks (index score 4+), less distinct streaking on the head and neck, and less brown on the back. And they often gave the impression of a slightly broader (fluffier) neck and fluffier forehead than the typical Common.

2) James Smith has posted photos of some other pale redpolls he saw along with the previously-reported Hoaries on Cape Ann; and Marshall Iliff photographed one obvious and five probable Hoary Redpolls on Cape Cod last week. In both cases these are birds that, like my New York photos, stand out among Common Redpolls but are not quite pale enough to reach everyone's threshold of "safe" Hoary. So let's call them intermediates until we have a better understanding of variation. I think they're closer to Hoary than to Common, so it would be wrong to call them Common with no further discussion. If anyone with more redpoll experience is willing to offer an opinion on any particular bird the discussion could be very helpful.

For comparison, here is a Swedish bird carefully-diagnosed as a 1st winter Hoary (so I'm not the only one calling such dark birds Hoaries).

3) On bill size as a distinguishing feature of redpolls: look at this page of variation in bill size of European Hoary Redpolls (scroll down for Hoary). Here is photographic evidence that bill size is not very useful for identifying Hoary and Common Redpoll, and this answers the question I posted previously about bill shape - Hoary can have a bill just as slender as the typical Common.

4) I agree with Ron Pittaway's point on ID-Frontiers that Redpoll identification is especially challenging in photos, since the differences are so slight and are strongly affected by lighting and image processing. The most useful photographs are often those with multiple birds rather than full-frame portraits, and I would urge photographers to try to include several redpolls in each image so that any Hoary candidates can be compared to adjacent birds under identical conditions.