Sighting Record for Utah

Common name:	Pomarine Jaeger
Scientific name:	Stercorarius pomarinus
Date:	October 25, 2024
Time:	2:45 p.m.
Length of time observed:	~2 hr 15 min
Number:	1
Age:	Juvenile
Sex:	Unknown
Location:	Farmington Bay WMA
County:	Davis
Latilong:	40.952962 -111.937246
Elevation:	4,202
Distance to bird:	125 yards
Optical equipment:	8 x 42 bins; 85 mm scope w/20-60x zoom
Weather:	Hazy sun
Light Conditions:	Bright but glaring low angle sun
Description: Size of bird:	Medium gull
(Description:) Basic Shape:	Gull
(Description:) Overall Pattern:	Dark chocolate brown
(Description:) Bill Type:	Gull-like; hooked
(Description:) Field Marks and Identifying Characteristics:	Dark chocolate brown and very gull-like. Much larger than the Franklin's Gull that it pursued, killed and ate over much of the observation time. Bill: Thick, long, gray-blue base with prominent black hook making up distal 1/3. Gonydeal angle obvious in one photo, but not overwhelmingly prominent. Smoothly-rounded crown in most postures during a long observation period. Plumage in resting posture on water: Uniformly chocolate brown head lacking streaking or pale nape. Cinnamon tones on nape at long distance; I couldn't tell if it was the plumage color or an artifact of light. Dark chocolate brown upper-parts lacking pale edging. Sides paler brown than chocolate and with a warmer, slightly cinnamon tone. Blurry dark and light barring on flanks merged into strong, straight, black and white barring on under-tail coverts, or at least the sides of the under-tail coverts. Plumage in flight and while struggling with prey: Upper surface of wings showing six pale primary shafts when the wings were open. Underside of wings showed a large white crescent at the base of the primaries and a second, much smaller crescent at the primary coverts. Barring on under-wings narrower, blurry and not as contrasting white/black as undertail coverts. R1 retrices short and blunt (not seen but captured in photos). Feet medium gray, toes small and webbed. (see photos)
Song or call & method of delivery:
Behavior:	Bird was resting on the water mid-pond when I first noticed it, but just before that, the flock of 130 avocets had just billowed up off the pond and resettled. In retrospect, the jaeger was probably arriving and flushed the avocets because I couldn't find any other reason for their upheaval. The jaeger then proceeded to take an extensive bath, as in 15-20 minutes of bathing and preening. Then, it took off and flew east into the waterfowl rest area flying neither tern-like nor falcon-like, but gull-like--powerfully, but not in a terrible rush or making a bee-line. It circled the rest area once, not chasing anything; not flushing anything; and then landed among the hundred of thousands of black and brown birds. I lost sight of it and practically wept. Minutes later, it flew back across the road and started pursuing a Franklin's Gull that was flying in front of it. The jaeger struck the gull twice, forcing the gull into the water, and then dropped into the water as well. The jaeger repeatedly attacked the gull over the next 15-20 minutes until the gull was dead, and then consumed the gull over the next hour and a half or so. The jaeger took one short circling flight away from the gull during this time, then returned to the carcass and resumed feeding.
Habitat:	Large, freshwater, shallow pond in an extensive marsh.
Similar species and how were they eliminated:	From Long-tailed Jaeger: Subject bird was bulky, powerful and gull-like unlike the delicate and tern-like Long-tailed. Subject gull was also much bigger than the Franklin's Gull it killed; a Long-tailed would be about the same size and unlikely to kill a Franklin's Gull. From Parasitic Jaeger: Large bill with large hook and noticeable gonydeal angle instead of pencil-like thin bill; smoothly rounded crown most of the time instead of the Parisitic's slightly peaked crown; lacking streaked face and pale nape; uniformly barred undertail coverts instead of irregularly barred. All dark gulls: None show a double primary flash or short, blunt extended R1 tips.
Previous experience with this & similar species:	None with Pomarine or Long-tailed; four Parisitics in Utah; the common young dark gulls annually, especially California and Herring.
References consulted:	Sibley, Kaufman's Advanced Birding, Macaulay Library
Description from:	Notes taken at the time of the sighting From photo(s) taken at the time of the sighting
Observer:	Kristin Purdy
Observer's address:	Ogden, Utah
Observer's e-mail address:	**
Other observers who independently identified this bird:	Bryant Olsen
Date prepared:	October 26, 2024
Additional material:	Photos
Additional comments:	I thought this bird was a Parasitic when I first saw it because of the cinnamon sheen on the neck and the bill looked small at the significant distance. It's amazing how easily that great big bill faded into the distance when seen at only a slight angle. I had a niggling doubt about how boldly black-and-white the under-tail coverts appeared, which isn't consistent with Parasitic. I posted an eBird checklist to get the word out quickly, and later changed the ID when I watched the bird kill the gull. Also, I waded out into the pond and closed the distance by at least a third so I could gain more info and better pictures capturing field marks. The bill and crown shape were apparent at the closer distance, but also by then, I had seen the double primary flash as the bird flew back from the waterfowl rest area just before killing the gull. I offer this info to explain why I first reported Parasitic and then changed it to Pomarine with better information. Sure am glad I keep my rubber boots in the truck.