Sighting Record for Utah

Common name:	Parasitic Jaeger
Scientific name:	Stercorarius parasiticus
Date:	9/12/2023
Time:	12pm~
Length of time observed:	20 minutes
Number:	1
Age:	immature
Sex:	?
Location:	Antelope Island Causeway
County:	Davis
Latilong:	41.085113, -112.164957
Elevation:	4200ft
Distance to bird:	200m at closest
Optical equipment:	Nikon 10x42 Binoculars, Kowa 88mm Spotting Scope
Weather:	Partly cloudy, calm 75F
Light Conditions:	Good
Description: Size of bird:	Flying, no frame of reference, smaller than gulls it chased
(Description:) Basic Shape:	gull like
(Description:) Overall Pattern:	uniform dark chocolate brown
(Description:) Bill Type:	Piscivor
(Description:) Field Marks and Identifying Characteristics:	Spotted a Jaeger flying to the SE of the 2mm on Antelope Island Causeway, proceeded to get photos as it flew over causeway heading north, then got the scope on it as it continued north, eventually caught a thermal, soared, changed direction and headed east and chassed gull at Weber river outflow on to mudflats, lost it as it continued east. A dark morph, very dark chocolate brown overall, some mottling on under wing making it an immature bird, white base to primaries on underside but dark greater coverts, white shafts on 4 primaries on upper side, tail short with short 2 R1 tail plumes, shape not seen in the field but look pointed in photos. bill long and thin, gray with small black nail less than 1/3 length (assessed from photos). All dark undertail coverts. Flight fast and direct(falcon like), harassed gulls in fast agile flight. I believe this is a different individual Parasitic Jaeger than the one seen and photographed here on 9/10, that bird was an intermediate morph with a paler whitish belly. (see photos)
Song or call & method of delivery:	None heard
Behavior:	Flying south to north, then headed east and chased gulls
Habitat:	Wetlands and mudflats of Great Salt Lake
Similar species and how were they eliminated:	Long-tailed Jaeger-bill should be shorter with nail making 1/2 of length, white shafts to primaries on upper side only on 2 outer most primaries, longer but blunt R1 tail feathers. Usually have barred black and white undertail coverts, even on dark morph immatures. Smaller and more delicate, more buoyant tern like flight style Pomeraine Jaeger-overall bulkier. Bigger bill with more prominent nail on bill. R1 tail feathers blunt not pointed. Usually barred black and white on undertail coverts, even on dark morph immatures. Have "double flash" in underwing, base of greater coverts also white.
Previous experience with this & similar species:	Yes, my 10th in Utah. Many in Alaska and at sea. Many with both Long-tailed and Pomarine in Utah, Alaska and at sea.
References consulted:	Sibley app, Macaulay Library photos
Description from:	Notes taken at the time of the sighting From photo(s) 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:	None that I know of
Date prepared:	9/14/23
Additional material:	Photos
Additional comments:	eBird checklist: https://ebird.org/checklist/S149731116