BIRDING BY HINDSIGHT: A Second Look at Jaegers
“A challenge that has innumerable angles and complications” is how Kenn Kaufman describes it. He goes on to say it’s “difficult to find any one field mark that cannot be matched by ... another species.” And when considering post-juvenile immatures, he warns there are “almost no plumage characters for separating the species.”
I believe him. Early in July at Cape Race, Newfoundland — the place where the first distress signals from the Titanic were received, by the way — our group was watching this bulky, broad-winged, pot-bellied jaeger lumbering after Black-legged Kittiwakes in awkward pursuit. The kittiwakes were clearly smaller by a wide margin: obviously, this had to be a Pomarine. Even Dave Shepherd, our local escort and expert who watches jaegers all the time, said so. But then the scopes came out to reveal two short but clearly pointed central tail feathers, and there was no trace of the Pomarine’s trademark double white patch on the under wing. This Parasitic Jaeger was sinking our confidence in jaeger ID faster than any iceberg!
I’ll bet Debi Shearweater, pelagic birding guide, believes him. She related an anecdote in which this jaeger flew by her boatload of skilled experts off the Pacific coast – and all three species were confidently called out!
And readers of the “Frontiers of Field Identification” listserve better believe him. In September 2005, photos of a jaeger in Utah were posted by the observer seeking ID help from experienced jaeger-watching subscribers. Scholarly analyses were posted in reply, and the observer reported their opinions a few days later: twelve said Long-tailed; nine claimed it was Parasitic. The photos then were posted on a site in Belgium, and — you guessed it! — the initial consensus among experts there was Pomarine.
Clearly, when it comes to jaegers, even those with lots of experience are often befuddled. So what chance do we have in Minnesota, where jaegers typically appear only as occasional September specks on the Lake Superior horizon? [Author's Note, August 2016 – In recent fall seasons, several jaegers (mostly Parasitics) have been studied and photographed at relatively close range at Wisconsin Point in Superior, WI.] None of us can claim to be experts, especially when it comes to non-adult jaegers, and all of us need to exercise extreme caution when reporting anything above the “jaeger, sp.” level.
But, surely, there must be some guide books which adequately address this ID problem? Well, don’t count on your trusty Geographic field guide to be much help: here there are only 13 pictures (of dubious artistic merit) on two pages, not nearly enough to get you very far. The Sibley Guide to Birds is much better, with 47 better illustrations spread over four pages, but the problem with jaegers is much larger than even Sibley’s guide has room for.
Perhaps the best place to start is with Kenn Kaufman’s A Field Guide to Advanced Birding. This often overlooked book from 1990, the source of the quotations cited earlier, includes several good chapters on difficult ID problems, and its treatment of jaegers is still very useful even after 17 years. As suggested by those three quoted caveats, though, this chapter wisely does not attempt to provide all the answers.
Providing all those answers, allegedly, is Skuas and Jaegers by Klaus Olsen and Hans Larsson, a comprehensive book devoted entirely to the world’s four species of skuas and three jaegers, with eight useful color plates of jaeger illustrations, many pages of exhaustive (and exhausting) text, and lots of photos. But there’s almost too much here. I find the text wordy and convoluted with truly useful information hard to extract, and, while many photos illustrate the useful field marks, almost as many images seem to contradict what the text and other photos claim.
So, no matter where you turn for help with jaeger ID, some questions will remain unanswered, and this article certainly has no delusions about being able to resolve them all. It does hope, however, to discuss which are the right questions to ask, and one way to approach the subject is to consider it in four parts: 1) jizz or gestalt (i.e., non-plumage field marks); 2) field marks useful on adults only; 3) field marks for jaegers of any age; and 4) field marks of juveniles and older immatures.
Jizz
In places like Minnesota, where jaegers tend to be seen mostly in flight at a distance, examination of subtle plumage features is seldom possible. Accordingly, a jaeger’s jizz or gestalt — or whatever term you use to describe non-plumage features — becomes an important consideration. By definition, though, such features tend to involve only subjective impressions rather than objectively solid and measurable distinctions.
But here are some factors of jizz which seasoned jaeger-watchers often include in their field notes and sketches and consider in combination with other factors:
• Overall size. If possible, compare the wing span and body length to another known species — like that gull or tern it’s chasing. However, like we were at Cape Race, be prepared to be completely fooled by size considerations. And, if there is nothing available for direct comparison, your impressions of size would be shaky at best.
• Overall shape and bulk. Similarly, judging shape (including the body’s apparent center of gravity) and overall bulk would matter only when there’s direct comparison with something. But here’s the scary part: according to Olsen & Larsson, female jaegers are 11–17% larger in weight than males of the same species! It’s also scary and amazing that this crucial statistic remains unknown to so many birders. Obviously, then, unless you know how to determine a jaeger’s sex, take a long and hard second look before basing your identification on size and shape.
• Wing shape and position. This would include your impressions of the width of the wing where it meets the body, how much of the body projects in front of and behind the wing, and the size of the so-called “arm” (or basal half of the spread wing) compared to the “hand” (from the bend of the wing outwards).
• Flight speed. But please don’t assume that any slow-flying jaeger is a Pomarine. Parasitics fly just as slowly when in relaxed mode: i.e., when not in pursuit of something.
• Aggression. It’s more helpful to consider flight style tendencies when a jaeger is chasing something — or being chased in retaliation. Long-taileds generally show less aggression towards nearby gulls and terns; Parasitics are usually the most aggressive. Parasitics are the most acrobatic and maneuverable during pursuits, and Pomarines are the least so. Similarly, Parasitic chases tend to be the longest, while Pomarines tend to give up more quickly.
• Season and location. I have little evidence to support these impressions, but here goes: In Minnesota, a jaeger in late fall (after, say, about mid-October) will likely turn out to be a Pomarine. Or, a jaeger in summer may well have a tendency to be a Long-tailed. And, if you find a jaeger away from Lake Superior or other large lake, you might want to start thinking in terms of it being a Long-tailed.
Again, take note of these features, and then start poring through your copy of Olsen & Larsson to see if anything adds up. Remember, though, that no single aspect of jizz amounts to much unless combined with other field marks.
Adult Jaegers
To simplify things here, let’s consider a jaeger with both a black cap and fully grown central tail feathers (rectrices) projecting beyond the rest of the tail to be an adult. A decent look at the length and shape of those rectrices should be enough to make an ID, but be sure to note: that these feathers on a Pomarine can be just as long as on any Long-tailed; that a Long-tailed’s central rectrices can be broken or still growing and appear short enough to suggest a Parasitic; and that the length of these rectrices on some Parasitics can approach Long-tailed proportions.
Other features to be aware of on adult-plumaged jaegers (beware, however, of older immatures which can appear adult-like and may not be safely identified by these field marks):
• Dark-morphs. If you’re sure it’s a dark-morph adult, it’s either a Pomarine or Parasitic. Dark juvenile (and older immatures; see Fig. 144 in Olsen & Larsson) Long-taileds do occur, but full adult Long-taileds reportedly “never” exist as dark-morphs.
• Breast band. Light-morph individuals of any of the three species can have a complete, or partial, or missing breast band. Note, however: no breast band is suggestive of a Long-tailed; a partial band or smooth wash suggests it may be a Parasitic; and a heavily mottled/barred band possibly indicates a Pomarine.
• Upper wing surface. Grayish wing coverts contrastingly paler than the darker secondaries = Long-tailed (but see the Parasitic in Fig. 73 in Olsen & Larsson); no contrast between coverts and secondaries = Parasitic or Pomarine.
• Under wing surface. A uniformly dark under wing with no white patch in the primaries = Long-tailed (although the outermost primary shaft may be white); white primary patches = Parasitic or Pomarine.
• Underparts. Grayish on under tail coverts and belly extending forward of the legs (when standing) or up to the center of the wing (in flight) = Long-tailed; darker/grayish area limited to under tail coverts on light-morph bird = Parasitic or Pomarine.
• Sides and flanks. Extensively barred or mottled = probably a Pomarine, but possibly Parasitic; no barring or mottling = all three species possible.
• Cap and malar areas. If you’re lucky enough to see a light-morph adult at close range, take photos or careful notes on the extent, contrast, and color of the blackish cap, especially in the malar area. Then consult the illustrations in Kaufman (p. 94) or in Sibley (p. 197–199) to see if you were able to detect any diagnostic differences.
Jaegers of Any Age
There are only a couple of field marks which are generally applicable to jaegers of all ages and morphs, and to base your ID on them is usually tricky:
• White primary shafts. There is an average difference among the three species in the amount of white showing on the upper wing: Long-tailed with the least amount of white; Pomarine with the most; Parasitic in between. But what many observers fail to understand is that the differences are on the primary shafts, not on the actual feather webs or vanes. Birders should also be aware that Kaufman considers this feature useful only if you’re sure the wing is fully spread to see all the shafts, and thus it’s “rarely much help in field identification.”
Note as well that Kaufman, Sibley, and Olsen & Larsson fail to agree on the meaning of how many white (or whitish) shafts you see....
Sibley: 1 or 2 = Long-tailed
3 = Long-tailed or Parasitic
4 or 5 = Parasitic or Pomarine
6 = Pomarine
Kaufman: 1 or 2 = Long-tailed
3 = Long-tailed or Parasitic
4 or 5 = Parasitic
6 = Parasitic or Pomarine
Olsen & Larsson: 1 or 2 = Long-tailed (but see the Parasitic in Fig. 73)
3 = Long-tailed or Parasitic or Pomarine (!)
4, 5, 6, 7, or 8 = Parasitic or Pomarine
So, there you have it. If you consider all three sources, you’ve clinched an ID (i.e., Long-tailed) only when you’re sure it has no more than one or two white shafts. Otherwise, the best you can do is narrow it down to two species (i.e., Parasitic or Pomarine) when there are four or more white shafts — and you’ve gotten nowhere if there are three. (Again, though, be sure to look at the Parasitic in Fig. 73 in Olsen & Larsson: it shows only one or two white primary shafts plus contrastingly dark secondaries and sure looks just like a Long-tailed.)
• Bill color, size, and shape. If you ever manage to get close enough to a jaeger, look carefully at the bill, document its color, size, and shape (including its nail and gonydeal angle), and then consult p. 196 in your Sibley or p. 94 and 98 in the Kaufman guide to find out if you saw something useful. Bill color, often visible at a distance, might be the most useful feature, especially if clearly bi-colored (i.e., dark at the tip and pale at the base). It is often claimed that such a bill is most indicative of a Pomarine, but I’m skeptical. Several photos in Olsen & Larsson show obviously bi-colored bills on all three species, just as other photos show apparently all-dark bills for all three.
Non-adult Jaegers
Just as it can be hard to tell an older immature or sub-adult jaeger from an actual full adult at a distance, it can be equally difficult to determine if a jaeger is a juvenile or a one-year-old immature. Accordingly, since some of the features listed below are more consistent for juveniles, it’s always worth trying to age that non-adult jaeger first. The following field marks, by the way, are nicely listed as easily understood bullet points in Olsen & Larsson’s text — although, as mentioned earlier, be prepared to find photos which fail to support some of the claims in their text:
• Juvenile plumage. Clean-cut plumage overall with well-defined pale feather edges on the upperparts, wings, and tail coverts = a juvenile (i.e., when the features below are safer to use); less uniform feather edging overall suggests it’s at least a year old, with its set of field marks more equivocal.
• Overall color. Clear cinnamon or rusty plumage tones overall = juvenile Parasitic; no trace of cinnamon color = all three species possible (including an older immature Parasitic).
• Primary tips. Folded primaries which are cleanly and obviously white-tipped = probably a juvenile Parasitic; dark-tipped primaries with no trace of white = probably Long-tailed or Pomarine. The problem is that primaries weakly tipped with white can occur on all three species.
• Under wing pattern. Even many novice jaeger-watchers are aware of the Pomarine’s “double wing-flash” on the under wing: i.e., in addition to the white at the base of the primaries, there is a second and smaller whitish area on the primary coverts. Kaufman, though, warns this field mark is “not especially helpful,” and its presence or absence is “hard to judge.” I agree. While two prominent white patches suggests a possible Pomarine, see Fig. 83, 86, 99, and 109 in Olsen & Larsson – all photos of non-Pomarines with obvious double white patches. Conversely, if this
feature is clearly absent, it may suggest a Parasitic or Long-tailed, although it is lacking on a few Pomarines as well.
• Central rectrices. While many juveniles and older immatures lack projecting central tail feathers, many do have short ones which are visible and can be diagnostic: pointed tips = Parasitic (of any age) or an older immature Long-tailed; short rounded tips = Pomarine (of any age) or a juvenile Long-tailed.
• Head. A mostly whitish head and neck often suggests it’s a Long-tailed, although some heavily worn or “bleached” Parasitics or Pomarines might look just as white. Or, if the head looks streaked, it may well be a Parasitic, since the other two usually, but not always, have unstreaked heads. By the way, a non-white or unstreaked head = all three species possible.
• Lores. Darker lores contrasting with the rest of the head may be suggestive of a Pomarine, but they can also occur on Parasitics and Long-taileds (see photos in Olsen & Larsson). Conversely, non-dark lores = all three species possible.
• Nape. A paler nape might usually suggest a Parasitic, but a paler nape can also appear on some Long-taileds and Pomarines — again, see photos in Olsen & Larsson which contradict the text. And once again, you guessed it, a non-pale nape = all three species possible.
• Upper wing surface. Olsen & Larsson’s text claims a paler leading edge on the upper wing does not occur on Pomarines; however, some photos show otherwise. Thus, a paler leading edge = all three species possible; and, for that matter, a non-pale leading edge = all three species possible.
• Barring on tail and under wing coverts. Finally, if you have nothing better to do, try to determine how heavily the upper tail coverts, under tail coverts, and under wing coverts are barred, and if they are paler or darker than the adjacent parts of the plumage. Kaufman’s and Sibley’s guides superficially mention or illustrate some of these matters, and, of course, Olsen & Larsson go into great depths on all this, which I admit I fail to fathom. I guess I do have better things to do.
* * *
This article is long enough already, so let’s not even think about talking about skuas — even though, amazingly, they have occurred at least twice in nearby states. Anyway, if you get nothing else from this article, keep at least two things in mind. First, it's important to think about sex (when identifying jaegers, that is). And second, whether or not you pursue jaegers by boat to get a better look, don’t get sunk by the icebergs!