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Blowing the Lid off the Lid-nosed

March 13, 2008

I’ve been writing at length about jaegers recently. I am fully aware that these birds in particular appeal to a limited sector of the birding public, a group within a group who digs the challenge inherent in the difficult identifications. I admit I was not one of these people when I started this project. I mean, jaegers are cool and all, I think we’re all in agreement on that, but I hadn’t even given much thought to them specifically. In all my birding years in the midwest, I never even so much as sniffed a jaeger sighting. Even when I moved closer to the coast where they were more likely, they were still a mystery, a vague idea of a bird rather then actual flesh and feathers. That’s part of what makes them so attractive to me now. They, along with gull aging and close parsing of Myiarchus flycatchers represent, for me, the last frontier of birding. Working at the museum has been the impetus for me to tackle these things I maybe didn’t feel as though I had time or patience for before, and I’m thankful for that.

But I run the risk of going way off topic here. I guess what I’m getting at is that I probably wasn’t the only one who didn’t give jaegers much thought. They nest in inhospitable places and spend what time they aren’t out of reach on land, out of reach at sea. They are not easy birds to find, which leads to the lack of information about aging by plumage, which in turn leads to limited information in field guides, which (and here’s the kicker) leads to incorrect information in said field guide. Do you follow? I’m saying some field guides are wrong at worst and misleading at best. Which is, at long last, the point of this post.

For reference purposes I drew from my personal collection of relevant field guides which includes three from North America: Sibley, Nat Geo, and Eastern Peterson and the excellent Birds of Europe by Lars Jonsson (a field guide I don’t look at nearly enough, for the gorgeous illustrations if for no other reason). Thrown in for good measure are Kenn Kaufman’s Advanced Birding and the Steve NG Howell Alula paper I’d been using throughout the project.

Ok, then. Let’s talk about adult non-breeding Pomarine Jaegers (definite basic). This plumage gets the short shrift in NA field guides, mostly because of the perception that non-breeding jaegers are largely pelagic, and therefore not likely to be seen by birders on our shores. Plus the molt into basic plumage is completed while the bird is far off shore. This is backed up by both Kaufman and Howell. However, one wonders if this impression is likely to change as access to the pelagic reaches (especially in the east) increases. In any case, the only NA field guide with Pom Jeagers illustrated in def basic plumage is Sibley, in which, on page 199 if you have it handy, a bird labeled Light adult nonbreeding (Oct-Mar) is shown displaying many of the field marks of the alternate plumaged bird but looking a bit “smudgy” overall. The cheek is yellow, the cap is extensive, and the back is solid. Check it out, I’ll wait.

I had been using Sibley. And so, many of the birds in the collection I had identified as immature birds of indeterminant age because very few of them matched Sibley’s def basic bird very well, and oddly, those that did were taken in summer. Alternately, I would find birds such as the one below.

I was puzzled, until I got Howell’s paper. And read the following:

Note that adult non-breeding plumages look quite different from breeding plumages, and overall, suggest immatures: the neatly capped appearance is lost and the underbody has variable dark smudging and barring; the back and, especially, the uppertail-coverts usually have pale barring; and the R1 projections are shorter. The underwing-coverts remain solidly dark.

Hmmm, interesting right? That description doesn’t at all sound like the illustration in the Sibley guide. I was caught up in the perception that juvenile jaegers had plumage characteristics that I was used to seeing in other juvenile Larids, primarily the barring on the back caused by pale tips on the body feathers. As in the bird below.

But let’s flip that bird over to see the one defining characteristic of adult jaegers that can be observed in the field. Dark underwings. Juvenile birds and some younger immature birds always have extensive barring under the wings. This is why it’s so important for you collection skinners out there to spread your jeager wings. I had several older specimens that I had to be very careful pulling the wing out to see whether it was barred or not. Spread wings saves the trouble. Below is the same bird from before.

Perhaps the most useful (at least when dealing with museum skins) chart in the Howell paper was an illustration of five jaeger legs. The pattern of pale versus dark on the tarsus changes predictably as the bird ages in Parasitic and Pomarines, but not in Long-tailed. Parts of the legs darken as the bird ages, with the adult birds showing a completely dark leg. Even as bare parts fade in museum specimens, I was still able to determine whether the legs were all dark or had some lighter skin. So the confirmation of what I was seeing in the wings, I saw again in the legs. Note the legs of our example bird below. Even with the pale-fringed body feathers, the barred undertail coverts, the indistinct facial pattern, the shortened central retrices; all characteristics that in any other bird would be indicators of a juvenile, were betrayed time and time again by the underwings and the legs. I pulled out bird after bird that was incorrectly labeled as a juvenile, when they in fact, it was an adult bird in definite basic plumage.

So, how many field guides get this right? Sibley, for one, gets it wrong. But that’s not a critique of the field guide as a whole, which is justifiably considered the best one for North America. The Peterson guide was largely worthless, showing only adult birds and one juvenile bird, and the Nat Geo guide illustrates a 1st summer bird that is somewhat arbitrarily different than the juveniles, a distinction that Howell even finds difficult to make so one wonders why this is the plumage that needed illustrating in a major field guide.

That said, the best, most detailed, most thorough depiction of jaeger plumages was in the Lars Jonsson Birds of Europe. Not only are the paintings great, but Jonsson completely nails the seemingly inconsistent nature of the definitive basic jaeger. It would be nice if he showed the barred back more clearly, but beggars can’t be choosers, I suppose.

So why do Sibley and so many others get it wrong? I certainly don’t mean to imply that it’s a comment on Sibley’s skills as an artist and birder, because come on, it’s David freaking Sibley we’re talking about here. I suspect it’s the same issue that I had when I began this jaeger project. There is a dearth of quality information out there on aging them by plumage, and what exists is relatively recent. Many of the birds I ended up calling Definite Basic were mismarked as Juveniles for the same reasons that I had been calling them Juveniles in the beginning. Traditional Larid aging calls on us to note specific plumage characteristics that don’t appear to be consistently reliable when applied to jaegers. I’ll bet the NC museum is not the only institution with this problem, and it trickles down when illustrators use these incorrectly labeled specimens as models, transferring this misinformation into their books.

So there it is. A new way to look at Jaegers? Maybe, though they still remain birds that many birders see far too infrequently to be completely comfortable with. And I freely admit that aging them, in addition to simply identifying them to species, probably puts me well within the realm of the completely obsessed. But all in all I found it pretty cool.

Oh, and I could be completely wrong about all of this. Just keep that in mind too.

  1. slybird permalink
    March 13, 2008 8:38 am

    Great post.

    I wish our collection prepared birds with one spread wing like that. So much more is visible. Unfortunately, the space our collection takes up would increase by many times. Oh well, I guess we don’t really need those cubicles upstairs…

  2. Charlie permalink
    March 13, 2008 8:49 am

    Excellent post N8. Jaegers are really tough birds to ID, and I have to admit I’ve nowhere near the experience to be sure of the ID in the field of most of the jaegers I see unless they’re bog-standard adults or I see them well enough to get a really good feel for their size and bulk etc. Aging them has always been a problem – and I’m often dumbfounded that birders who see the darn things even less than I do feel able to confidently age them at 500m in a storm…

  3. Jochen permalink
    March 13, 2008 10:10 am

    To me, Jaegers, or skuas, or “Robbery Gulls” as the Germans name them, are best identified by their flight stile at long distance:
    Tern = Long-tailed
    Black-headed Gull = Parasitic
    Common/Herring Gull = Pomarine

    A perched Jaeger/Skua/Robbery Gull on the beach is a nightmare…

    And as for ageing them… well. Oh, but look over there, the Prothonotary perched on a red herring!

  4. Mike permalink
    March 13, 2008 10:48 am

    Nice one, N8. I’ll try to keep this in mind if I ever see a jaeger!

  5. noflickster permalink
    March 13, 2008 2:47 pm

    Nicely accessible tour through the challenges of jaegers, I love your writing. Regarding jaegers, unfortunately for me, I will promptly forget everything in the excitement of actually seeing one, should the opportunity ever arise. When is global warming going to bring those pelagics closer to western NY??

    Slybird, don’t be eyeballin’ my Dilbertesque-cubicle space . . . .
    – Mike

  6. March 13, 2008 3:52 pm

    Such is the downside of spread wings, we have several birds where we just take the wing off, stick it in a sleeve and file it separately. Of course, this means I have to track down the wing then…

    While I know more than I did before, I certainly would not count myself among those with lots of jaeger experience. Your field experience with them sounds like mine.

    Perched jaegers? Why, that’s when you look at the legs.

    Good luck. My first birds were a long time coming, and just as difficult as everyone says they are.

    Mike (noflickster)-
    Thanks for the kind words. I’ve always thought my writing was a bit haphazard and stream-of-consciousness. Glad to hear someone enjoys it. : )

  7. slybird permalink
    March 13, 2008 5:18 pm

    We take separate spread wings too, but not in any systematic fashion. Just occasionally.

  8. Jochen permalink
    March 14, 2008 10:22 am

    Yeah, NOW I will…

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