by Donna L. Dittmann & Steven W. Cardiff

"A" is for AGE; "B" is for BODY SIZE; and "C" is for CENTRAL RECTRICES ----the first three things to assess as a jaeger approaches. Then, "D", "DON'T JUMP TO CONCLUSIONS!," "E", EVALUATE plumage and soft part details (bill and leg color), and "F", note the upperwing and underwing FLASH (can you actually count the number of white primary shafts?). Finally, if possible, "G", GET a series of photographs or video tape (a single picture rarely shows enough detail to clinch an ID). Sounds simple? Sometimes, but not always.

Like their relatives the gulls, jaegers have distinct alternate, basic, and juvenal plumages, as well as sub-adult (first basic, second, and third year) plumages. Sub-adult plumages of jaegers are less clear-cut than those of gulls, increasing the difficulty of determining relative age. Further adding to the complexity of jaeger identification is that all species exhibit plumage polymorphisms (light, intermediate, and dark morphs). Most field guides only illustrate standard plumage types: light and dark morph alternate-plumaged adults, and a generalized immature or juvenal plumage. Such treatments greatly over-simplify identification problems of this group, and create confusion because many jaegers observed do not neatly fit the field guide descriptions. Birds of the Western Palearctic (BWP), Vol III (Cramp et al. editors, 1983) provided a modern accessible reference that included a detailed sequence and description of jaeger plumages. Although the text is difficult to assimilate, it is still our personal favorite reference. Seabirds, an identification guide (Harrison, 1983) was the first field guide to address jaeger plumages in detail (introducing many observers to definitive basic plumage), and was followed by Advanced Birding (Kaufman, 1990). Both of these sources provide helpful information to augment standard guides. Skuas and jaegers, a guide to the skuas and jaegers of the world (Olsen and Larsson, 1997) is the next step up for those particularly interested in jaeger identification. This guide is the most detailed to date, and includes 7 color plates and 93 black and white photos devoted to jaeger identification. It is the first guide to illustrate some of the more difficult birds to identify: worn and bleached individuals, birds in active molt, and sub-adults.

Despite all the published treatments of the problem, jaeger ID continues as one of the foremost challenges for US birders, especially along the Gulf Coast where it is difficult to gain experience because jaegers are generally few and far between, and where even fewer individuals allow close, leisurely studies. Jaegers are generally inaccessible, and only one species, the Pomarine Jaeger, is currently regular in Louisiana in any numbers. Also compounding matters for Louisiana observers is that a large proportion of birds that will be encountered will not be in definitive alternate plumage, thus making it difficult to practice "jizz" of individuals of known species.

Jaeger Identification Characters

When you observe a jaeger, what features should you look for? Few single field marks are "diagnostic" for any one species. As mentioned above, the ABCs are a good way to begin. A bird's age is important, so as to put observed field marks into proper context. Underwing lining color, shape of central rectrices (= middle pair of tail feathers or "T1s"), undertail covert pattern, and leg color are helpful to age an individual. Non-dark juveniles and sub-adults have barred or checkered brown and white wing-linings; these linings get progressively darker as the bird ages. Underwing linings are solidly dark in adults at all times of the year, but note that some dark morph birds (Pomarine and Parasitic jaegers) can have essentially all dark underwing linings at any age. Leg color of all juvenile jaegers is bright blue with just the distal half of the foot (toes and webs) black; the rest of the foot and leg darkens with age (except Long-tailed Jaeger; most individuals retain a juvenile-like pattern). Undertail coverts are black in adults, barred in juvenal and sub-adult plumages; the pattern and coloration of the bands is helpful for species recognition in fresh plumage (generalizations: crisp even-width bands of dark brown and white in Long-tailed and Pomarine, more wavy, less defined, rusty-white and brown in Parasitic).

Body size and shape is another helpful starting reference point. Jaegers are sexually dimorphic with respect to body size, males generally smaller than females. There is overlap in size between Long-tailed and Parasitic, and Parasitic and Pomarine jaegers. Because jaegers rarely pause next to more familiar species for direct comparison (other birds generally do not want to associate with them) it can be difficult to get a good relative size assessment. Jaegers also maneuver quickly around their hapless victims, and apparent size seems to fluctuate from moment to moment. Further confusion may result from comparing light-colored birds (gulls and terns) to dark-colored jaegers, or from deceptive viewing conditions at sea. In general, Pomarine is about the size of or bigger than a Ring-billed Gull; Parasitic, about the size of or bigger than a Laughing Gull; and Long-tailed, more or less the size of a Franklin's Gull. Pomarine, the largest species, also tends to look the bulkiest, possessing broadest-based wings (primaries appear proportionately shorter and narrower than the broad secondaries), and a proportionately short, broad tail. Long-tailed is the smallest species and typically appears proportionately long-and slender-winged and has a proportionately long tailed and overall graceful appearance. Parasitics are in between, but generally are more Pomarine-like in overall proportions. It is often possible to recognize extreme individuals by size, proportions, and flight style in the absence of other field marks - but this is a risky proposition in most instances. Beware of subjective dogma regarding size and jizz (e.g., "barrel-chested Pomarine," "tern-like Long-tailed"). Such descriptions may only misdirect you from a correct ID. These statements are oversimplifications and were no doubt derived from extreme individuals. Your jaeger-time will be more productively spent studying and describing diagnostic suites of characters. On the water, jaegers have a distinctive silhouette; compared to a gull, jaegers' long wings give their rear end a more "tipped-up" appearance.

The central rectrix shape of alternate-plumaged jaegers is well-covered in all field guides. Only Pomarine possesses long (often twisted) or short, wide, and blunt or rounded T1s. Whereas both Parasitic and Long-tailed have pointed T1s of various lengths (based on age and stage of molt), only Long-tailed has proportionately very long and slender T1s. T1 shape, presence or absence, may also be of importance at other times of the year. The T1s of juvenile Long-taileds are short and rounded versus more pointed feathers on Parasitics; T1s of 1st and 2nd spring Long-taileds are often worn to a thin, thread-like projection. The T1s are molted twice a year in Pomarine and Long-tailed; these species may lack T1s (or appear that way) during molt, and possess short T1s in basic plumage. Parasitics shed their T1s only once a year during a complete post-breeding molt.

As noted above, "D" stands for don't jump to conclusions based on your initial impressions of age, size, and tail. Continue to observe the jaeger as long as possible, noting as many of the important plumage features as possible (see illustration). Remind yourself that ID characters in this group are largely subjective and subtle, and that, in many cases, only well-studied combinations of features will allow a positive ID.

The number of pale primary feather shafts can be crucial to identification. The majority of jaegers show the following pattern: Long-taileds (2), Parasitic (4-5), and Pomarine (5-6). Although there is some variation within species in number of white shafts, the extremes of Long-tailed (2) and Pomarine (6) are essentially diagnostic. Not to be confused with the pale primary shafts, all species have white bases to the primary feathers (see illustration); these contrasting white areas create the wing "flash." The amount of white visible as the primary "flash" on the upper surface of the wing is directly related to the degree the individual feathers are spread in flight and whether they are covered by the primary coverts (worn or molting birds appear to have a much larger flash if the coverts are worn or missing). Only adult (and older subadult) Long-taileds can show essentially no upperwing flash; Pomarine Jaeger typically shows the largest flash. Underwing flash is produced the same way. Again, only adult Long-taileds are essentially "flash-less". Some Pomarines (unlike the other species) can show a second light crescent area basal to the "flash" (a double-flash). Beware of individuals in wing molt and/or with very worn outer primaries as this may affect the number of white shafts present or the overall effect of the wing flash.

Other important features include: 1) Contrast of upper surface of the wing. Adult and advanced sub-adult Long-taileds have a distinct contrast between the paler back and upperwing coverts and the flight feathers. This pattern is less obvious in Parasitic, and essentially lacking in Pomarine. 2) The pattern of underparts can provide insights into age (presence or absence of breast band, pattern of undertail coverts) or plumage stage (alternate vs. basic). Head pattern can also provide clues (streaking or light patch at base of upper mandible present on Parasitics). Bill shape is also helpful. Parasitics have proportionately long, slender bills with only a slight hook. Both Long-tailed and Pomarines have more prominently hooked bills, Long-tailed relatively short and thick as compared to a Parasitic, Pomarines appearing generally more massive in all proportions. The coloration of the bill can also provide clues: adults show all dark bills, whereas subadults and juveniles are usually bicolored. 3) Presence of barred upper tail coverts may be suggestive of a particular species (e.g., prominently barred, and essentially almost "white-rumped" at a distance may indicate Pomarine), or sub-adult or basic plumage.

Plumage characters are affected by wear and molt. Assessing the presence of molt or wear can be especially helpful to determine a bird's age/plumage type. "Fresh" plumage is usually indicated by paler feather tips (prominent in juveniles). As the feathers wear, the lighter tips are abraded off; prolonged wear will result in more ragged-edged or broken feathers. Worn feathers may become bleached by the sun, taking on a "blonde" appearance. Extreme wear may even "skeletonize" feathers to the point that only the shaft remains. In general, jaegers are in relatively "fresh" plumage by early to mid-winter (juveniles fresh in late summer-fall). Basic plumage is acquired by a complete molt that includes all of the body and flight feathers (except for juveniles that have a partial body molt and retain juvenal flight feathers until the following summer/fall). Birds molting from alternate to basic plumage may be observed during fall migration and early winter: jaegers encountered during this period will likely appear in a transitional plumage and show gaps in the wing or tail (missing or growing-in flight feathers). Alternate plumage is acquired by a partial body molt that is usually begun on the wintering grounds and proceeds during spring migration, often not fully completed until after arrival on the breeding grounds. During late winter and spring, birds may appear in transitional plumage (molting from an immature-like basic plumage to alternate plumage) and Long-taileds and Pomarines may appear shorter-tailed as they grow in their alternate T1s. Individual variation in degree of body molt varies greatly in first summer and other sub-adults. Summering individuals found in Louisiana often fall into this category, being extremely worn, bleached, and generally ratty. They may possess different generations (ages) of feathers, from fresh to nearly skeletal. Onset of pre-basic molt in these non-breeders may begin as early as late spring. These birds represent the greatest identification challenges as they often seem to defy age determination and stage of molt. Summering birds are often in poor condition, and may seek sanctuary on beaches. Surprisingly, jaegers are often more difficult to identify when they are holding still - sitting on the water or standing on a beach. This is because many of the "diagnostic" characters such as wing pattern, tail, undertail, etc. are concealed. Thus, onshore jaegers, even those accompanied by extensive photographs, often prove difficult to identify conclusively, especially if there are not any flight photos.

"G" is for get photos. Photographers will have an obvious advantage in capturing details for subsequent analysis; the camera or video tape sometimes captures marks not noticed or not well-resolved by the eye. With a good set of photos, identifications can often be resolved long after the bird has disappeared (sometimes years later!). As for those sight records, once the jaeger disappears over the horizon, immediately jot down as many details as possible. Hopefully, the sum of all the characters observed will enable you to determine age class, plumage type, and species identification. Speaking from experience, don't count on being able to remember the details later, as the next jaeger in view (or the next, or the next) may blur your memory of the preceding one. Remember, few jaegers readily fit the "standard fieldguide" plumages.

Status of Jaegers In Louisiana

Our knowledge of the status and distribution of jaegers in Louisiana waters in largely incomplete due to a lack of offshore coverage. What little data is available suggests the following patterns of occurrence. Pomarine Jaeger appears to be an uncommon spring and fall transient, and winter resident offshore. This species is occasionally encountered during the summer, when stragglers are sometimes seen onshore. Many observations of this jaeger have been from nearshore waters, where it is usually observed harassing gulls behind shrimp boats. By watching aggregations of birds feeding behind shrimp boats, the likelihood of seeing this species, especially during the last week of April and early May (when often in full alternate plumage) is good (contrary to the belief that Parasitic is the inshore jaeger). It is regularly observed on the Sabine CBC just off East Jetty at Cameron. It has also proven to be the most numerous jaeger in deeper offshore waters. Pomarine Jaeger was removed from the LBRC Review List in September 1997. Both Parasitic and Long-tailed jaegers are currently on the LBRC Review List. Records of Parasitics are scattered throughout the spring, fall, and winter. It is probably more common than reported, with the paucity of records likely attributable to the lack of coverage. To date, there are only two accepted records of Long-tailed Jaeger for Louisiana. Both are documented with specimens: Cameron, 24 April 1965 (Louisiana Birds, Lowery 1974) and from off South Pass, 28 May 1990 (8th Report of the LBRC, Dittmann & Kleiman, ms). This species is probably a regular transient in blue water off Louisiana and potentially a rare summering species.

All three species have been reported at various inland sites during hurricanes or tropical storms, although few records are currently accepted to species. All species are possible on large inland bodies of water during migration, particularly in fall (when reported from many other inland sites throughout the United States).

Quiz (use other references as necessary): What species of jaeger is depicted in the accompanying illustration, and why. Can it be identified? Hint: observed offshore during May. – LSUMNS, LSU, Baton Rouge, LA