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.

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.