Well, they may not be the best jaeger photos, but we feel it is almost always helpful to have photos to discuss and learn from, regardless of quality.
These distant, blurry but identifiable photographs were obtained by Jake Mohlmann about 3:00-3:30PM on 24 September 2008 from Site 6 at Lake Havasu. Fortunately for us and for Lauren Harter (the original finder of the bird), this jaeger species at this age in this color morph is relatively easy to identify. I emphasize relatively because jaegers are almost never "easy" to identify - except, perhaps, in perfect adult breeding plumage. I'll let the literature do the talking for our first image.
Ocean Birds of the Nearshore Pacific, Rich Stallcup (1990):
"Unlike the other two species, some juvenile Long-taileds are pale-headed...The dorsal light grayness, contrasting a black trailing edge to the wing, is indicative of Long-tailed Jaeger for young as well as adult birds."
Blurry though it may be, a dark trailing edge to the wing is discernible on the above bird (click to enlarge it). While the front half of the bird may be slightly washed out due to lighting conditions, the pale head is still quite obvious. That may look like a collar on the side of the neck, but it's not well-defined or dark (as it should be in other jaeger species). Check out The Sibley Guide's illustration of light immature Long-tailed Jaeger to see what I mean.
This isn't a fantastically useful shot, but at least it shows the contrast of the pale head to darker upperparts again.
If you were still scratching your head (why isn't this just a wonky gull of some kind?) check out the above picture confirming the whitish-based flight feathers classic on virtually all plumages of all 3 species of jaegers. Normally those pale bases to the primaries are not so conspicuous from the upperwing - that's more of a Skua feature - but the light shining through from the underwing is playing tricks on us. Now here you have to use your imagination a bit, but if you inspect the pictures very very VERY closely, you can just barely make out a white feather shaft or two on the leading primaries...really. Maybe squint and tilt your head a little... Ok, maybe you can't see it here, but we were pretty sure we could see it in the field!
I like this one because even though the whitish primary shafts/feathers are heavily blurred due to wing (and camera?) motion, it still shows how limited the white is. Not necessarily a 100% reliable mark, but very little is 100% when it comes to jaegers. A combination of factors is necessary to clinch an ID. Anyway, Long-tailed Jaegers show no more than 2 white primary shafts (note: NOT the primaries themselves, the actual feather shafts); Parasitic, the most likely candidate for confusion, shows 3-5. Interestingly, though the uppertail coverts were barred black-and-white, the white seems to come through more than anything else on these flight shots.
That's all we have on our end, but you can check out Lauren Harter's photos of the bird sitting on the water (note the strongly black-and-white barred undertail). Also, this bird from Kentucky looks virtually identical to the one we saw. The KY bird is really interesting because much like our bird, there are a few confusing marks that, when considered in isolation, could be construed as indicative of a different species. When taken in combination, however, the ID becomes clearer.
One more interesting link: http://www.idahobirds.net/identification/ltjaeger.html. (If you were wondering about the big white patch underneath the wing in our 4th picture, check out the underbody images on this page.)
Hopefully someone else can come up with clearer, more diagnostic photos, but these will have to suffice for now. We're not finished checking references yet, so if we come up with any more enlightening pointers on these pics, we'll be sure to update!