Sighting Record for Utah

Common name:	Parasitic Jaeger
Scientific name:	Stercorarius parasiticus
Date:	9/19/2023
Time:	10:00am~
Length of time observed:	2 minutes total
Number:	1
Age:	immature
Sex:	?
Location:	Willard Spur
County:	Box Elder
Latilong:	41.373717,-112.133503
Elevation:	4,200ft~
Distance to bird:	200-400m
Optical equipment:	Kowa 88mm spotting scope
Weather:	Partly cloudy, 70F, calm
Light Conditions:	Excellent (sun was low to the SE, bird was to northwest and north)
Description: Size of bird:	slightly smaller than Ring-billed Gull
(Description:) Basic Shape:	gull like
(Description:) Overall Pattern:	dark blackish brown
(Description:) Bill Type:	not seen
(Description:) Field Marks and Identifying Characteristics:	Initially seen chasing a gull to the north and watched for 30 seconds doing so, fairly close, then when I tried to go from the scope to binos to camera, I got on a nearby juvy CAGU instead and lost it. I stayed in the area scanning with the scope and binos and about 10 minutes later re-found it flying to the north from NW to E farther out and watched it in the scope as it flew directly east, but lost it as it went over the dike into Willard Bay. My notes: "Immature dark morph, uniform blackish brown with paler( but not white) belly, large fast agile and powerful in flight chasing a RBGU, which it was slightly smaller than, short pointed R1 tail plumes seen well, mottled underwing with single primary flash, upper wing not seen well, GISS and behavior of PAJA. Total viewing time of about 2 minutes, mostly in the scope. 200-400m out"
Song or call & method of delivery:	None heard
Behavior:	Flying the entire time I viewed it
Habitat:	Freshwater to brackish wetlands of Willard Spur, also flew into open freshwater of Willard bay
Similar species and how were they eliminated:	Long-tailed Jaeger immature-longer but blunt R1 tail feathers. Smaller and more delicate, much smaller than RBGU, more buoyant tern like flight style, not as fast and agile in flight, often don't chase other birds. Pomarine Jaeger immature-overall bulkier and as big as or bigger than RBGU. R1 tail feathers blunt not pointed and barely project past tail if at all. Have "double flash" in underwing, base of greater coverts also white. Not as fast or agile in flight.
Previous experience with this & similar species:	Yes, my 11th in Utah. Many in Alaska and at sea. Many with both Long-tailed and Pomarine in Utah, Alaska and at sea.
References consulted:	Memory
Description from:	Notes taken at the time of the sighting
Observer:	Bryant Olsen
Observer's address:	84102
Observer's e-mail address:	**
Other observers who independently identified this bird:	Kris Purdy also saw a Jaeger here on 9/17 and again later the same day I did on 9/19, and again on 9/20, presumably the same bird.
Date prepared:	9/20/2023
Additional material:	Photos [by Kris Purdy]
Additional comments:	My eBird checklist: https://ebird.org/checklist/S150284556 Kris's Checklist(with photos): https://ebird.org/checklist/S150312352