ML608176171

Age

Not specified

Sex

Not specified

Observation details

Juvenile jaeger. I have gone back & forth and round & round on this ID, but I finally alighted on Long-tailed as the best match amongst the jaegers. Photos to follow: -- Bill: 1) Pale with dark tip (I thought initially about 1/3 dark, but when I put a ruler to the bill in photo DSCN6914 and measure from the tip of the hook, it really is more than one third). 2) Bit of a gonydeal angle argues against Parasitic 3) Fairly short bill good for Long-tailed but also argues against Parasitic (though seems constant with the proportions of a Pomarine in some field guides) -- Head shape: The head shape is very round, which is most consistent with a Long-tailed, less so for Pomarine, even less for a Parasitic. -- Tone: I would argue that this bird is warmer brown than is shown for juvie Long-tailed jaegers, but this is a subtle thing and may be due to the intense late afternoon light (which tends to imbue a warmer hues to things on this planet). I don't know. -- Barring: The bird was heavily barred above and below the base of the tail. This is consistent with either a Long-tailed or Pomarine, but less so with a Parasitic. -- Tail: In the field through the scope, the central tail feathers appeared to extend one or two inches past the rest of tail and the projection looked squared off. But a closer look at the photos shows that the projections do taper a bit, thus bringing the tail within the range of any of the the three. -- White pattern on the top surface of the wing. 1) The pale bases of the primaries struck me as too extensive for a Long-tailed through binoculars in the field, a better match for a Parasitic or maybe Pomarine. But the photos show a more subtle paleness. Perhaps this pale crescent pattern is accentuated by the late afternoon low-angle light, but it still troubles me. (See photos DSCN6884 & 5). 2) The white primary shafts limited to outer 2-3 feathers definitely match a Long-tailed. -- White patch on the under surface of the wing. This "flash" caused by the pale bases of primaries is present in all three species. However, a Parasitic should have a "double flash" caused by pale bases to the primary coverts forming a second line below the main flash. We did not see a double-flash in the field nor see one in photos (see photo DSCN6899). So that argues against Parasitic. -- Greater coverts: Pale central spots in greater coverts are usually not found in Pomarine, but are common in the other two species. This all but eliminates Pomarine. -- Timing: According to Bryant, Long-tailed Jaegers tend to migrate earlier in the fall migration than the other two species. -- Body Shape: The bird had a fairly attenuated shape, supporting a Long-tailed jaeger. I find this a bit difficult to judge in the absence of the other jaegers for comparison, seeing as the body shape appearance changes with position and angle. But I agree with Mark this bird's body shape is best for a Long-tailed. The wings seemed long & thin. Filed marks that neither support nor detract: -- head darker than torso -- vague chest band -- heavily barred under wing -- flight fairly languid and wing beats seemed relatively shallow

Technical information

Model

COOLPIX P1000

ISO

100

Focal length

359 mm

Flash

Flash did not fire

f-stop

f/6.3

Shutter speed

1/640 sec

Dimensions

4608 pixels x 3456 pixels

Original file size

3.41 MB