[Birdnet] Farmington Bay Jaeger

[Mark Stackhouse]

I finally made it out to Farmington Bay today to take a look at the 
jaeger. I must have been there earlier than the Beyers, because the 
bird was close to the road in the SW corner of the rest area (main 
impoundment on the left), where it stayed for some time before making a 
lengthy flight over the water, trending NE, until I lost it in the 
distance on the far side (E) of the impoundment, where it sounds like 
the Beyers found it. Also there while I was there were Eric Huish (who 
initially found it), Tuula Rose and Ned Bixler, all from Utah County.

I looked with great interest at the photos that Tim took of the bird 
last week, and had formed an idea as to what the bird is, but wanted to 
reserve final judgment until I had a chance to see the bird itself. 
I've found the best way to identify jaegers is by shape and flight 
style, something that's hard to see in photos. I just got back from my 
Washington Coast Tour, where we saw all three species of jaegers, plus 
South Polar Skua, so I feel in good "jaeger practice." We saw more 
Pomarine's than the others, but I managed to photograph all three 
jaegers.

What I saw at Farmington Bay today confirms what I thought from Tim's 
photos. I'm confident that this is a Parasitic, and not a Pomarine 
Jaeger. The bird I saw today was too slight of build, with wings too 
long and narrow to be a Pomarine. Although I never saw in in the 
classic, falcon-like flight it exhibits when in pursuit (something that 
Tim noted seeing in an earlier post), in the rather stiff wind this 
afternoon it was very buoyant and maneuverable looking in flight, 
showing none of the heavy, ponderous flight style (more like a large 
gull) of a Pomarine Jaeger. It's body appeared way too slim for a 
Pomarine (but maybe it's losing weight here).

Kris Purdy noted a good feature for these two species when sitting on 
the water - the extension and angle of the tail/wing tips over the 
water. The Parasitic shows quite a bit of wing/tail extension over the 
water, and it angles upward more than in Pomarine. This bird was much 
more like Parasitic in this character.

I noted two things in Tim's photos that suggested Pomarine - the fact 
that in some photos it looked somewhat heavy-bodied, and that a double 
light crescent could be seen on the underside of the wing tips in some 
photos. As I already noted, I couldn't see anything like the heavy body 
of a Pomarine on the bird today, and had trouble making out the double 
crescent as well. I had already discounted the double crescent, as this 
is a lighter-colored juvenile individual, and Parasitic usually shows a 
bit of double crescent in this plumage. A light Pomarine would show a 
much more obvious double crescent than this bird has. I think the 
heavy-look of the bird in some of the photos is due to the angle of the 
bird (jaegers tend to look heavier-bodied in head-on views).

Supporting Parasitic in Tim's photos are the fact that it lacks bold 
barring on the undertail coverts (something I noted today), and that 
the head is not contrastingly paler than the body/back, as would be 
more typical in pale Pomarine. The contrasting pale base to the tail is 
more typical of light Parasitic as well, giving the look of a dark 
terminal tail-band.

The caveat always is that in juvenile jaegers none of the plumage 
characters are 100% reliable - that's why shape and flight style are so 
important. In these this bird looked all Parasitic to me - which is 
unfortunate, as I was really hoping for a Pomarine. I've never seen a 
Pomarine in Utah, but this is my fifth Utah Parasitic Jaeger.

Mark Stackhouse
mark at westwings.com
801-487-9453 (Salt Lake City, Utah, USA)
011-52-323-285-1243 (San Blas, Nayarit, Mexico)