DBQ answers

12 01 2016

I got quite a few responses to this one, and I am not surprised that our usual ringers were right in here with both the clear i.d.s and the one that is, at least somewhat, in question. All three birds are ducks which all respondents recognized. The first two are in one category–ducks with a bluish speculum on the wing. Bird C is in a category of ducks with blue on the wing, but with that blue located on the upper wing coverts rather than the secondaries as in Birds A and B. Let’s take the Bird A/B pairing first.

I like when I have an all duck quiz since I can use Samuel Carney’s Waterfowl Wing Key. When we follow through that key for a bird with blue or purple on the secondaries, we get to a junction point where we are asked what borders the blue or purple patch. If it is hemmed in with white both above and below (that is to say, with white on both the greater coverts and on the trailing edges of those blue/purple secondaries), then we have a mallard, like such:

800px-Mallard_pair_in_flight

Mallards in flight. (Photo by Ingrid Taylar)

In this photo, one can see not only the clearly bordered speculum, but another helpful feature for when you have the underside of the wing to look at as well–a mallard’s underwing is a clean, clear white. This is in contrast to our other candidate among the blue-speculumed ducks, the American black duck, which has a characteristic brown streaking on the underside of the wrist.

An American black duck (ABDU to friends) is generally described as having no white border, front or back, around the blue, though in many images and in some descriptions, one may see a faint pale trailing edge to the secondaries. It’s pretty faint though. Great, so that was easy, no? White borders: mallard. No white borders: ABDU. Not so fast (0f course). Because these two species heard we were having an easy time of their identification, they decided to hybridize freely. Given the slight chance of pale tips to the secondaries in an ABDU, we can look at the forward border of the speculum for a firmer sense of what is happening here. In an ABDU, there should be no white at all on the greater coverts at that leading edge of the blue speculum. So, where are we now with respect to Birds A and B? A shows substantial white both fore and aft. Bird A looks like a mallard decisively to me (my decisiveness here is augmented by back up from most of our respondents on this quiz). Bird B has what we might technically term a “meh” amount of white on that forward border of the speculum. It’s faint, but it’s definitely there. While some of our quiz players think ABDU on this one, others raised the possibility that this is one of those ABDU x MALL hybrids, and I am inclined to agree. Would that we had more of the bird to go on, but the features here do seem intermediate between the two species.

Now, to Bird C. This one is in the group of ducks with a large amount of blue on the upper wing coverts rather than the secondaries. It’s hard to know if the secondaries ever had much color–they may have, but as my next blog post will address, blues and greens in bird feathers are a trick of the eye, and in a disheveled specimen, those colors may be lost almost entirely. In addition, in some species, the secondaries are green and iridescent in males, but green and non-iridescent (dull) in females. I don’t see much that catches my eye in the secondaries of Bird C at all, but if there is any green there, I would say it looks decidedly non-iridescent to my eye. What we have to go on is the blue, and then some white on the greater coverts, though they do not appear entirely white–more dark spotted with white rims. In the group of birds with blue on the coverts and a white band on the greater secondary coverts, our best candidates are blue-winged teal and northern shoveler (both raised by our respondents). How to differentiate them? The number one feature all the field guides point to are the distinct white shafts of the primaries in northern shovelers. Take a moment to appreciate them in this image:

 

Screen Shot 2016-01-12 at 11.05.37 AM

USFWS photo

As you can see in these images, the white band on the greater coverts in northern shovelers is uninterrupted, unlike the broken band with dark spots we have in Bird C. In addition, I do not see these obvious white primary shafts in Bird C. Taken together, these two features lead me to call this a blue-winged teal, and again, I draw unnatural courage in this i.d. from the fact that it came to me pre-identified by Craig Watson who works for USFWS down south, and also, so many of our crack dead bird experts told me they thought it was a blue-winged teal as well. I hardly ever see these, so I confess, I would not have come up with that right off the bat.

Next time, I will share with you what I’ve been reading about feather pigment, honest signals, and the flamboyant tails of motmots in the Yucatan.





Dead Bird Quiz: got the blues edition

8 01 2016

It’s a monochrome world outside here in the north, and, though I am secretly wishing for snow so I can get some cross country skiing in, I do appreciate a spot of vibrant color. Thus, I have made these selections for the DBQ. Though they are not the most challenging ever, this will give me a window to talk about pigment in feathers when the answers are revealed, so look for that next week.

Here are our candidates (a phrase I hear a bit too often for my liking here in New Hampshire these days; I can’t travel 5 miles without tripping over a would-be President).

Bird A: found by Dan Tracey in Massachusetts in May.

DTracey7594-22573

Bird B: found by Ray Bosse, also in Massachusetts, also in May.

rbosse7498-21529

Bird C: guest Seanetter Drew Lanham, professor at Clemson, photographed this bird on New Year’s Day on Seabrook Island, SC.

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DBQ answers II

14 12 2015

No more shirking or dodging; I must at last face those wings known as Bird B. To jog your memories, here’s what we’re working with:

DMinsky7855-24633DMinsky7854-24633

Dennis, who found the wing, wondered if this might not be something other than a standard issue species. Everyone who has looked at the wing (and ventured to reply) concurred that this is a loon of some kind. The clean white underwing by itself could indicate a few different species groups, including shearwaters and grebes. But looking at the upper wing, we see buff colored chevrons at the terminal ends of the secondary coverts. The wing chord looks to be around 28cm. These features together tell us this is a loon, and a pretty small one (common loons have a wing chord in the 33-40cm range). Red-throated loon is the default i.d. for a small loon on the east coast, but it’s not the only possibility. Dennis granted that it could certainly be a RTLO, but thought something just seemed a bit off about in terms of its overall coloration and the nature of those pale chevrons. Since Dennis has seen many, many a dead bird, I think it worth a look when he notes something atypical about a carcass. Dennis thought perhaps Pacific loon should be on our consideration list. If we consider Pacific, we should also consider Arctic since the two are almost always uttered in the same breath and can be difficult to distinguish themselves. Both Arctic and Pacific loons would have a wing chord in the range of Bird B’s; both average larger than RTLO, but a wing chord of 28cm would fit with any of the three species. Strangely, given what one might assume from the names, the Arctic loon would be much more of a rarity than the Pacific in these parts.

This situation calls for the use of two of my favorite resources: Peter Pyle’s identification guide, and the Slater Museum’s online wing collection. You can check out a whole suite of loon wings from various species and times of year here. Fortunately for me, they have a few Pacific loon specimens there to look over, in breeding and non-breeding coloration. As with many loons, breeding plumage includes bold, clear, pure white spots on otherwise black upper wings. Our Bird B does not have any white spots or dots at all, but that lack is typical of a bird no longer in nuptial raiment. Beyond being a non-breeding bird though, what we have here in Bird B appears to be a young bird. In the case of RTLO and Pacific loon, both have pale edges to the secondary coverts during the first year, and that first year plumage is retained into well into the first winter, so the timing is right for Bird B, which was found at the end of November.  To parse out the differences between juvenile RTLO and Pacific loon wings, we can look at Peter Pyle.

IMG_7742.JPG

Secondary coverts in Pacific loons. In juveniles, a pale, terminal band gives the impression of light, nearly white crescents over the upper wing.

IMG_7743

Contrast the preceding with these secondary coverts from RTLO. The far left image is a juvenile and the pale coloration here is much narrower and comes to more of a point, giving an impression of chevrons rather than crescents.

Considering this, I am of the opinion that Bird B is decidedly chevroned and now crescented. And so, though I had fervently hoped we might have a first ever Pacific loon in our database, I fear it is not, and is, instead, our old friend the Red-throated loon. As ever though, if I am missing something critical, I know all you super-pros will write it with the correction.





DBQ answers part two

11 11 2015

And now we return to the continuing saga of dead birds. Bird B, you will recall, was little more than a skull and some other odd bone bits. Remember Bird B?

DMinsky7701-23584

Responses as to the identity of Bird B were split between common eider and some sort of goose. Indeed, this is a waterfowl type of bill, with a sloping profile and some serrations on the bill margin. The profile is quite smooth from bill to forehead, with no knob or other protrusion anywhere along the bill’s length. This is our general impression when looking at the profile of a live common eider, especially since they have those fleshy lobes that run backward up over the forehead.

Note the fleshy lobes on the eider bill, more prominent in males like this.

Note the fleshy lobes on the eider bill, more prominent in males like this.

 

If you look at the skulls of eiders, which you can do at Wouter’s skull site here, you can see the bone structure that underlies those lobes in the rearward projections over the forehead. Our Bird Blacks these. The other respondents on this quiz listed various goose species as contenders, and to throw an additional bit of support for that into the mix, Dennis’ note when he found this bird noted that the wing bones seemed extremely large for a duck. But within the geese, which species? Responses included Canada goose, cackling goose, and barnacle goose. There is a bit of black and white feathering still adherent to the bones in Bird B, consistent with any of those three. Barnacle goose is far rarer in these parts than the other two, but not unheard of certainly. Cackling goose sounds like something unusual, until one reads a bit about it and finds out that cackling goose is the designation given to what used to be considered merely a very small race of Canada goose. Genetic analysis has determined that cackling goose is its own distinct species. Whether or not we can, from just a photo of the skull, determine if this is cackling goose or Canada goose is a dubious question indeed.

But within these geese candidates, now is the perfect time to send you over to Wouter’s Skullsite which is an absolutely marvelous resource that I know I mention often, but with good reason. If you refer to the Anatidae (ducks and geese) page of that site here, you can get a look at the comparison between barnacle goose and Canada goose. Barnacle geese in life have what we might term a “cute” face. (Cute being a highly technical term). We tend to find animal faces cute when they have outsize eyes for their faces, and if you look at the barnacle goose skull, you will see that its eye socket (or orbit) is quite large. Compare that with the size of the orbit in the Canada goose. I would argue that the overall shape of not just the orbit, but the squared off back of the skull in our Bird B as well as the length of the bill compared with the length of the skull all argue for Canada (or cackling) goose rather than barnacle goose.

Finally, we have Bird C, which presents a substantial identification challenge. Indeed, there is really not enough here to get us to species. Everyone responding figured we have a duck here, and I concur. Edward suggests there might be a tiny hint of a blue speculum, leading us perhaps to American black duck, but neither he nor I am entirely convinced of its presence. Wouter did want to venture beyond saying it’s a duck, Mark and Jim did not venture a guess (and I can’t blame them), and John Stanton took a stab in the dark and guessed Bufflehead. So how did people know this was a duck? Wouter points to the only real clue we have–the sternum.

WMumford878-14180

This affords us an opportunity to use another of my favorite sites, aves3d.org. Take a look at this image of a surf scoter sternum, rotated to reflect the same angle we have on Bird C:

Copyright Harvard Museum of Comparative Zoology and Aves3d.

Copyright Harvard Museum of Comparative Zoology and Aves3d.

There are substantial similarities here–the overall blocky shape of the sternum, the crescents cut into the rear facing edge, and the flared projections beside those cutouts. Similar enough to make a species call though? Maybe. Take a look at these comparative images of the sternae of some other ducks:
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Somewhat surprisingly, since the surf scoter seems such a close match, the black (or common) scoter is actually dissimilar to Bird C in many ways: the crescents are more pointed in the black scoter and there isn’t as much of a pinched in, hourglass shape the sternum overall. The common eider sternum beside it actually looks a bit more like Bird C, but here the lateral projections look a bit too rounded and blunted at the ends. I might actually be inclined to call this an unknown scoter. I don’t have good skeletal reference material for white-winged scoter, which would be another candidate. We don’t see evidence of a white speculum in Bird C, but these wings are extremely weathered and bleached overall, so I am not sure how much stock I really want to place in that. I think unknown scoter might be pretty good for an i.d. What say you, esteemed dead bird colleagues? As always, your thoughts or directions to additional reference material are always most welcome.





DBQ answers, saving every 30 seconds version

6 11 2015

OK, after mourning the loss of all the work of yesterday’s post, I am now ready to try and recreate it. Bird A was universally identified as a black scoter, and I’m not surprised. Given that we have both feet and wings, our odds of getting to species are fairly high. But how did everyone arrive at that conclusion? I find the feet to be the most eye-catching aspect here.

Dabbling duck foot (left) vs. diving/seaduck foot.

Dabbling duck foot (left) vs. diving/seaduck foot.

These are webbed, waterfowl type feet, but the toes are thick and fleshy, with a prominent lobe to the hind toe. These are no dabbling feet; these are the feet of a hardy, seafaring sort of duck. Within seaducks of this general size, we are looking at eider or scoter. The overall coloration of the bird is dark, so we can rule out common eider. Though males do have quite a lot of dark on them, they would also show some white, particularly on the upper surface of the wing near where the shoulder would once have been. Similarly, if this were a white-winged scoter, we would see white here too, this time in the form of the eponymous speculum. But we have a pair of wings dark throughout, and dark on both upper and lower surfaces. So we have surf scoter and black scoter remaining. In terms of the foot, if you take a look at this fantastic shot from Arkive.org, you’ll see a pretty good color match between a confirmed black scoter and our Bird A. Surf scoters, on the other hand, seem always to have some degree of reddish cast to the toes, even in the youngest birds and in females. See this charming illustration from long ago:

Surf scoters. Note even the female (left) has reddish toes.

Surf scoters. Note even the female (left) has reddish toes.

Here’s one final thing: in all our references, indeed even in the Field Guide I researched and wrote myself, one of the defining, nay, the defining characteristic that permits differentiation of a SUSC wing from a BLSC wing is the relative length of the outer two primaries. That conventional wisdom is that in BLSC, the outermost primary is shorter than its neighbors. In a SUSC, the outermost primary is equal to, or longer than its neighbor. This can be subtle, and is most helpful in a wing where the primaries have been fully extended. It’s hard to tell where the outermost primary actually ends in Bird A, even in this zoomed in image.

Closeup--is that a short primary I'm seeing there?

Closeup–is that a short primary I’m seeing there?

When we refer to a major authority on the subject, Carney’s guide to waterfowl based on wing plumage, we see an artist’s rendition that looks much clearer, not surprisingly, than field conditions often are.

Reference: http://digitalmedia.fws.gov/cdm/ref/collection/document/id/1407

Reference: http://digitalmedia.fws.gov/cdm/ref/collection/document/id/1407

It may be the power of suggestion, but the more I look at Bird A’s wing, the more convinced I am that I am seeing a skinny little outermost primary overlain on a broader, longer, next-door-neighbor primary. So, I find myself on board the Black Scoter train with all of you.

Now, on to Birds B and C, but at the moment, I am out of time, and if I break this into a two part cliff hanger, I will have something to write about next week. I’ve been at this blogging game a while now, folks, and I’ve learnt a few tricks. See you next time for the further installment of DBQ answers.





I divulge the secrets of quality control

20 10 2015

Many thanks to Dennis Minsky who wrote me with questions about the process by which a bird identified as one species by the volunteer mysteriously changes to a different species in the database. Dennis even suggested it might be a worthy blog post, and I concur. So here it is, the secret sauce.

When you folks submit a walk report, dead birds or no, I look it over. The only things I really look at in terms of the environmental data you report is to see if the time seems correct (did you really walk at 3am, or did you just slip when entering am/pm?) and check if there are any notes you left me about your walk.

If you do find a dead bird, the process of verifying your data is necessarily more involved. We are proud of the fact that we can present our data with assurances as to the accuracy of the species reported, because, as you know, we require you all to take photos of every bird you find. Many of you are experienced birders, so I appreciate very much that even the most knowledgable among you still take the time to snap those pics. Because of that, we can say confidently that every beached bird is reviewed by a second level referee beyond the person who found the bird. That referee is, and has been since 2008 or so, me. If you submit a beached bird report, and you don’t include photos, your report will still be verified, but your beached bird i.d. will be changed to “Other, Unknown” and in the notes box at the bottom of the screen, you will see this:

 

Screen Shot 2015-10-20 at 3.03.12 PMI am not always confident in my i.d., especially with the carcasses in really rough shape. Anyone who reads this blog knows that, since my uncertainties are usually paraded in front of you as Dead Bird Quizzes. But not every beached bird photo makes it to a DBQ.

In many cases, you submit your beached bird report and photos, and then you check again in a day, a week, or, more likely, a few months, and that report has been checked off as verified, your bird i.d. confirmed. In some cases, you may go into an old report and find that your i.d. has been changed and no one told you. When that happens, it’s because I have gone in and reviewed the report, any measurements, and the photos, and come to a different conclusion than you did. I realize this is a somewhat opaque process since there is nothing to alert you that this has happened.

At the prompting of Dennis’ email, I have been thinking of how better to communicate with you about these cases. These revisions come frequently enough that individual emails are not possible, but what I can do is to use that “Notes about carcass” field to let you know how I came to a different conclusion than you did. Sometimes it will be a particular field mark or coloration pattern, sometimes a skeletal clue, sometimes it’s the measurements. I can appreciate that it will help you be a better birder of dead birds if I provide some explanation of that thought process. I will start giving that a try on my next round of verifications, which is already overdue. The beached bird reports wait for no man, nor for any college professor in the throes of mid-semester stress. My gratitude for your patience, Seanetters!





DBQ answers

7 10 2015

It’s fitting that both these DBQ birds come from the Carolinas; our volunteers and friends in both states have been much on my mind given the horrendous flooding in that region, and I know some of our walkers live and work right in the heart of the most heavily impacted areas. I hope everyone in the SEANET clan is safe and sound, and if it’s not TOO much to hope, that your houses remain high and dry. You’re in our thoughts all the time, southern friends.

For these southern birds, on the other hand, there is not consensus as to the i.d. of the second bird. The first, however, was obvious to all as a Laughing Gull. The giveaways: the dark, downcurved bill, and the black legs. These are typical of winter plumage LAGU like the ones seen in this photo:

"Leucophaeus atricilla P5190038ra" by Migdoniodiaz - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons -

“Leucophaeus atricilla P5190038ra” by Migdoniodiaz – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons –

I suppose it may seem strange that I chose this bird, since everyone seemed certain of its identity. Maybe it was just me, but the gray on the upperwings of this bird seemed really pale, no? What did you all make of that? Just a trick of the light? A really pale individual? Have you seen them this light before? I ask my southern contingent especially since, while we do have LAGU up here in the great white north, I don’t see them all that often in winter in plumage like this.

How about Bird B? This one drew a verdict of Black Skimmer from John Stanton, and whenever someone suggest Black Skimmer, I always think, “Oh! Right! Could be a skimmer! I always forget about them. Northern bias shows again since that’s a species I really don’t ever see. Out of sight, out of mind, therefore. But Black Skimmer needs to be on the list whenever we have a dark wing with white feathertips especially through the secondaries. I actually thought Bird B might be another Laughing Gull, so, I dutifully went to my Beached Bird guide and, using its wing key, I arrived at a page showing immature LAGU and immature Black Skimmer side by side. Sure enough, both have white tipped secondaries, though the skimmer’s are much more extensive, with a very wide white band, while the LAGU has much more limited white. The main difference the guide mentions is actually the color of the underwing, which is pale or mottled in LAGU and dark in the skimmer. I did not provide that image in the original post, so here is the underside of Bird B’s wings:

Photo by G. Grant

Photo by G. Grant

This is actually sort of not helpful, since much of the underwing has been eaten away, most likely by notorious ghost crabs. So it’s impossible to tell whether the feathers that used to be on the underwing close to the body were mottled or clear white, so I turned again to the upperside of the wing. There, I can see what looks to me like a few rusty feathers among gray feathers. Since Black Skimmer juveniles are more black and white on the upperwing, that rusty/gray contrast jumped out at me. I am fairly persuaded, then, that Bird B too is a LAGU. Two LAGU in one DBQ? Unprecedented. Daring. Accurate? I hope. But I await verbal combat from those who may disagree.





Dead Bird Quiz: back to school edition

30 09 2015

Hi Seanetters! I am back in the throes of teaching now, so much of my days are consumed by teaching, grading, listening to people whine, and all the usual teaching related stuff. Please forgive me, therefore, if I only manage one post a week for the next couple months. One thing is certain though: it is high time for a DBQ. Here it is.

Bird A, found by Lynda Zegers on her South Carolina beach in August.

Bird A's underside

Bird A’s underside

Upper surface of Bird A.

Upper surface of Bird A.

Bird B, found by Gil Grant on his North Carolina beach, also in August.
ggrant7656-23565





These shearwaters ain’t foolin’ nobody!

1 09 2015
These GRSH show off their competitive natures and their field marks. The birds in the background look like Wilson's Storm Petrels to me. (Photo: DickDaniels via wikimedia commons)

These GRSH show off their competitive natures and their field marks. The birds in the background look like Wilson’s Storm Petrels to me. (Photo: DickDaniels via wikimedia commons)

As anticipated, pro dead bird identifiers like the readers of this blog recognized the three species in the last post immediately. Bird A is a Greater, Bird B a Sooty, and Bird C a Cory’s Shearwater. Luckily for me, shearwater i.d. tends to be straightforward, and I have a few quick features I look for to make the call at a glance. For the Cory’s, it’s that yellow bill. As the field guides say, that is “distinctive” once you’ve established you’re looking at a shearwater. And the wacky tube nose is a giveaway on that. For the Sooty, the dark breast and belly are the decisive factor here; other shearwaters have white on the underside. The most common shearwater we get on SEANET beaches though is by far the Greater. When looking at a light bellied shearwater with a dark bill, it’s almost always a Greater. But I check every time for what I find the most reliable indicators. GRSH have a dark, smudgy patch on the belly. To the uninitiated, it can look like dirt, or even oil. You all, of course, are initiated, and know that. That is, however, why I chose Bird A particularly. The smudge is variable between individuals, and I found it interesting that it is basically absent in this bird. That did give me pause, so I double-checked with another of my go-t0s for GRSH, the undertail coverts (dark in Bird A). Among the white-bellied shearwaters, the Manx has white undertail coverts, while both the GRSH and Audubon’s have dark. So we should at least entertain Audubon’s when looking at a shearwater that has a white belly and seems to lack any dark smudging.

Though I didn’t provide a picture of the upper side of Bird A in the original post (not that any of you needed it), so I will do so now:

Other side of Bird A. Photo courtesy of L. Ries.

Other side of Bird A. Photo courtesy of L. Ries.

This Bird looks brownish overall on its upper surface. This is definitely a GRSH characteristic; Audubon’s shearwaters are much blacker above. Finally, if you look at the upper surface of the tail, you can see a disheveled pale band in evidence. This is also a GRSH feature; Audubon’s have an all dark rump and tail. The pale tail band also brings up one last species to keep in the back of our mind, though it very rarely turns up; the Black-capped Petrel is not a shearwater at all, but it is a tubenose with a white belly and dark upper side. What sets it apart, however, is a broad, clearly white band on the upper tail, and a sharp black band on the underside of the wing. I am always hoping such rarities will turn up, so I try to keep my mind open to them, and my oddball i.d. skills honed.





Dead Bird Quiz answers, part deux

29 07 2015

I admit, I feigned more mystery about the mystery sternum in the last post than was actually present. Emily, who sent the picture, was thinking it was likely a loon, and I did question that since the angle was so bizarre, but it is, most likely, a loon. Somehow, the angle of the photo obscures entirely all the attachments of the ribs, which makes the sternum look as though those projections jut out much higher than they likely do in real life (or real death). Mainly, I wanted to show people how cool Aves3D is. And I was holding out for an emu or dodo. A girl can dream, right? Well, until Jim writes in and posts a photo in the comments that shows the similarities between Mystery Bird A and a Common Loon. So, Emily was right all along, and I will move onto Bird B.

For Bird B, Mary Wright wrote in with an excellent walk-through of her i.d. The bird was identified as a jaeger by the original finder, Marcia Lyons, and Mary elaborated as to species. But first, how to get to jaeger. For me, it always starts with what the bird is not. We get a lot of gulls, eiders, that sort of thing on SEANET beaches, so when something like Bird B comes up, the brain jumps to common ones and tries to sort out why it’s not that. In this case, the wings are very much gull shaped, and the foot is reminiscent of a gull’s, but the coloration is unlike the gulls we typically see–dark above, but with white shafts on the primary feathers, and dark below as well, with a silvery white color to the underside of the primaries. The shape of the tail is also quite interesting: a wedge shape that generally brings to mind a cormorant, but this is most certainly not a cormorant. Shearwaters might come to mind, but the combination of very dark underwing contrasting with a white belly and breast defies the field guides’ shearwater section. Also, there’s still that weird wedge-shaped tail.

Slide3

Here’s that closeup of the upper wing again.

At this point, one might be reduced, as I often have been in the past, to simply paging through a field guide to find other possibilities. That is how I happened on jaegers and skuas the first time we had one show up on a SEANET beach. They are in the same family as gulls, so luckily, I didn’t have to page far. Skuas are larger than what we have here with Bird B, and their upper wings show not just white primary shafts, but typically a much wider swath of white where the primaries meet the primary coverts. Our Bird doesn’t have that. Jaegers then. This feels encouraging until one drills down on jaeger i.d. Our three possibilities are Pomarine, Parasitic, and Long-tailed. If we could rule out even one, we’d be feeling much better about ourselves, and indeed, Mary points to the way to do so. Counting the number of white shafts on the upper side of the primaries, I can see six definitely, and it looks like a seventh partly hiding. That’s quite a lot of white-shafted primaries, as it turns out. Pomarine Jaegers, especially young ones, are reported to have the most, with up to seven. Older Pomarines generally have fewer, but five or six is still typical. Parasitic Jaegers generally have only 4-5 of these white shafts, and Peter Pyle’s Identification Guide to North American Birds, vol. II tells me that again, juveniles have the most, with older Parasitics having as few as three. As Mary noted, Long-tailed Jaegers have only three white shafts, so our Bird B is wildly in excess of that. Based on the white primary shafts alone then, we might rule out Long-tailed and incline toward Pomarine, with Parasitic still in the running. Is there anything else we might glean from the wing tip alone, while we’re at it? Why yes! The tips of the primaries can give us some clues when looking at juvenile jaegers (and this assumes we are looking at a juvenile). Looking at the tips of these primaries, I don’t see any white or pale tips at all. If they were present, they could give us quite a clear idea what species this might be. Their absence, however, is not so definitive. Looking at this image from Pyle, we see two cases where white tips are entirely absent: Pomarine and some Long-tailed.

from Peter Pyle, Identification Guide to North American Birds, Vol. II

from Peter Pyle, Identification Guide to North American Birds, Vol. II

Reading the caption, however, we see that even when the white tips were present once, they are worn down over time, especially over the winter. Our Bird B was found dead in December, so we might cautiously conclude that the slow grinding of time was not responsible for the darkness of Bird B’s feather tips, and that our bird actually started out that way. Again, this would incline us toward Pomarine, (or Long-tailed, if we are still entertaining that possibility) and away from Parasitic. But this assumes we are dealing with juvenal plumage to start with, so I don’t want to set too much stock by that. Juvenile jaegers of all sorts have extensive barring over the whole body, including the wings. Our Bird B is a much more solid color overall–sort of a gray brown without much barring to speak of anywhere. Also, if we look at the leg color, they appear to be entirely black. Young jaegers have gray legs with variable amounts of black on the toes and feet. Adult Pomarine and Parasitic Jaegers have all black legs, whereas Long-tailed adults retain the gray on the legs. Score yet another point for ruling out Long-tailed. So why did I even mention points of identification for juveniles if the overall coloration and the leg color of Bird B show us that it’s an adult? Partly so I could show you how remarkable Pyle’s book is, with its exhaustive treatment of identification, but also partly because I was intrigued by a different feature of Bird B that struck me as juvenile-like and I wanted to find out more. That part is  the rump. And upper tail coverts, if you must know. Here, we have a few tantalizing feathers to look at.

Slide2

Just three, lonely, white tipped feathers on the upper tail.

Bird B is rather typically disheveled, for a dead, headless bird. But we can make out what looks like a whitish band on the upper tail (though this is quite possibly an artifact of dishevelment), and also three dark feathers with distinct white bands on their tips. Since the pattern of light barring on the upper tail is useful in differentiating juvenile jaeger species from one another, I wondered whether that barring disappears entirely in adults, or if any is retained. In searching the internet for clues, I found this beautiful shot of an adult Pomarine Jaeger in flight. You can see a few barred feathers on the upper tail here. Is this bird still in the last flush of youth then? Here’s another image, this one of another Pomarine in flight, but in this case, you can see all the spangling and barring on the underwing and flanks, which tells us that this is indeed a young bird, only partially in possession of its adult plumage (like that very grown-up yellow wash on the head). Here’s one last, of a breeding Pomarine Jaeger showing no barring on the upper tail at all. Are the barred upper tail feathers among the last to go then? That might explain the other juvenile features of our Bird B, such as the rather outrageous number of white-shafted primaries, typical of youngsters. The pale bands we see appear much more white than buff or cinnamon, which would be typical of a Parasitic. Again, then, I am leaning toward Pomarine on that count.

Now, how about that tail? Overall wedge-shaped, but our Bird B has two central feathers longer than the rest. This is a typical jaeger thing, but the exact shape and length of those two feathers can be helpful in deterring which species we have. Unfortunately, our Bird B’s central tail feathers (or rectrices) are beat up, so their former shape is close to indeterminable. In breeding adults, there are big variations between the three species. In juveniles, and also in non-breeding birds, the differences are less distinct, and that is the sort of case we have here, especially since, if this bird died in December, it was really transitioning between juvenile and adult plumage at that point. Overall, Parasitic Jaeger juveniles have pointed central rectrices, while Pomarine have blunt ones. I can’t honestly tell which we have in Bird B.

Finally, there is a feature of the underwing that can be helpful in telling apart the Pomarine and Parasitic that we might look to. In the Parasitic, there is a white band running along the primaries where they meet the underwing primary coverts. The Pomarine has this too, but also has an additional pale band that runs along the bases of the primary coverts. These features combined give the “double flash” appearance that Mary mentioned in her response. If you look at their respective underwings at the Slater collection here and here, you may be able to pick up on it, and also see how subtle it can appear.

Pomarine Jaegers of all ages and stages. Do you see the double flash? I'm not sure I do. Photo: Crossley Guide via Wikimedia Commons.

Pomarine Jaegers of all ages and stages. Do you see the double flash? I’m not sure I do. Photo: Crossley Guide via Wikimedia Commons.

Dark morph Parasitic Jaeger. I suppose those primary coverts do look fairly dark at the base? (Photo: pjt56 via Wikimedia Commons)

Dark morph Parasitic Jaeger. I suppose those primary coverts do look fairly dark at the base? (Photo: pjt56 via Wikimedia Commons)

So, after all that hemming and hawing, I feel that the weight of the evidence falls toward Pomarine, though not by a whole lot. Also, Mary is rather a good birder, and I am not, so I am still troubled by our failure to agree on this point. If we had the head, we’d be in much better shape, but we at SEANET are not accompanied to such luxuries. There is a certain spartan pride in that.