Sighting Record for Utah

Common name:	Parasitic Jaeger
Scientific name:	Stercorarius parasiticus
Date:	10-3-2024
Time:	11:30am~
Length of time observed:	15 minutes
Number:	1
Age:	1st cycle immature
Sex:	?
Location:	Antelope Island Causeway
County:	Davis
Latilong:	41.0655069,-112.2409049
Elevation:	4200ft~
Distance to bird:	200m at closest
Optical equipment:	Nikon 10x42 Binoculars
Weather:	Sunny, clear and calm, 70F
Light Conditions:	Good, some backlighting
Description: Size of bird:	Smaller than California Gull
(Description:) Basic Shape:	gull like
(Description:) Overall Pattern:	overall dark chocolate brown
(Description:) Bill Type:	Piscivor
(Description:) Field Marks and Identifying Characteristics:	Initially seen from the 2nd bridge chasing gulls to the west between the bridge and the marina in binos, Jaeger then flew south over the road in a glide, then descended to just inches above the water in fast flight heading toward me fairly close, then veered south and started chasing a California Gull in a fast direct pursuit, then landed on the water far out. I was able to get photos in flight and got the Jaeger in the scope on the water. Size: smaller than the gulls which it was chasing, especially the California Gulls. Age: 1st cycle immature dark morph. Underwing had pale edging giving a mottled appearance indicative of a immature. Overall very dark including belly, but a warm dark chocolate brown Bill: impression of bill in the field in the scope and from photos was long and slender without a prominent nail at the tip, consistent with a Parasitic Tail: fairly short but with longer rather pointy R1 tail plumes(from photos) Wing flash: The underwing had a prominent single flash of white from pale base of primaries, underwing coverts all dark, no "double flash" from pale base of primary coverts. Upperwing flash prominent with a pale crescent at base of primaries from pale shafts of outer 4 or 5 primaries, both consistent with Parasitic Overall impression of behavior and flight style: Flight was fast, direct and falcon like, observed chasing several gulls in agile wheeling pursuit, often going vertical upwards then spinning and diving on the gulls. I just did 2 Pelagics a few weeks ago and saw many of all 3 Jaeger species(plus 1 South Polar Skua) and the other Jaegers/Skua did not engage in the intense vertical pursuits that Parasitic do, I only observed Parasitic engaged in this behavior and my immediate impression from behavior of this Jaeger was Parasitic, which the plumage features seen in the photos confirm (see photos)
Song or call & method of delivery:	none heard
Behavior:	Observed in flight harassing gulls, then landed on the water and seemed to be loafing for some time
Habitat:	Open saltwater of Great Salt Lake and brackish water of Farmington Bay
Similar species and how were they eliminated:	Long-tailed Jaeger-smaller with a buoyant tern like flight, do not often engage in intense pursuit of gulls or terns, often hover and dive like terns. Upperwing flash limited to 2 outer primary shafts, have smaller bill with more prominent nail. Additionally Long-tailed are an earlier migrant then other Jaegers and although there are records from Oct., they are less likely this late. Pomarine Jaeger-larger(about same as California Gull) have a slower more lumbering gull like flight, do not often engage in long pursuit of gulls, only brief powerful direct brutish attacks, immatures usually show a "double flash" of white on the underwings from pale base of primary coverts and primaries. Also have very short tails with almost no projection of R1. Note, Hatch year Pomarine Jaegers remain in the Arctic much later than other Jaegers and are virtually unknown until November, even offshore on Pelagics only adults and 2+ year olds are seen until then, so any 1st cycle Jaeger at this time of year is highly unlikely to be a Pom.
Previous experience with this & similar species:	Yes, many. I just did 2 Pelagics a few weeks ago and saw many of all 3 Jaeger(plus 3 South Polar Skua) of all age groups(except 1st cycle Pomarine). I made a point to closely study every jaeger we saw to better my understanding of their GISS and behavior/flight style.
References consulted:	Memory
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:	10/3/24
Additional material:	Photos
Additional comments:	eBird checklist: https://ebird.org/checklist/S197384507