41-B-2018 Parasitic Jaeger

STATUS
Accepted
DATE VOTING COMPLETED
1ST ROUND
7-0
HOW MANY OBSERVED?
2 dark adults
DATE SIGHTING OCCURRED
DATE REPORT PREPARED
REPORTER
Austin R. Young
OTHER OBSERVERS
As far as I know, I am the only one to observe two birds in the same place at the same time. Steve Kahl and Cheryl Huizinga had seen single dark morph Parasitic Jaegers in the vicinity on the same day or two days before. Steve noted he may have had two birds two days prior but could not confirm. Steve Butterworth and Darren Clark observed a single Parasitic Jaeger in the vicinity two days later.
LOCALITY OF OBSERVATION
American Falls Reservoir, Power County, between the dam and Willow Bay recreation area. Specifically at: 42.8021,-112.8621
HABITAT WHERE THE BIRD WAS OBSERVED
The pair of jaegers were observed on the reservoir over open water.
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
I observed the birds well for 10-15 minutes. Both through 10x42 binoculars and a Leupold spotting scope. The weather was breezy, mostly cloudy, and cool temperatures. I first observed one bird about 150 meters away flying toward me, but most of the time the birds were several hundred meters away over the water.
DID YOU TAKE NOTES?
Yes, later the same day
DID YOU CONSULT A FIELD GUIDE OR OTHER REFERENCE WORK?
Yes, later the same day
WHICH GUIDE(S) OR REFERENCE(S): DID YOU CONSULT?
National Geographic Guide to Birds of North America (6th edition), Sibley Guide to Birds (2nd edition).
DESCRIPTION OF THE BIRD(s)
Clearly a member of the Stercorariidae family by their thin bills, long wings, gull-like shape, agility, and harassing behavior. Very similar in size to Ring-billed and California Gulls they were harassing. Both birds showed a conspicuous single white patch on underside of primaries and medium-length wedge-shaped tail.
BEHAVIOR OF THE BIRD(s)
Both were distinctly falcon-like in flight, as opposed to somewhat tern-like flight in LTJA and powerful and bulky flight as in POJA. Very twisty and agile flight when harassing gulls. Most of the time the birds harassed and rested on the water as a pair. Very similar in size to Ring-billed and California Gulls they were harassing.
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
The size of the birds and flight style were crucial. Also tail shape and pattern aided in identification. The fact that both birds were dark morphs also helped in the ID because ~80% of PAJA are dark morph and dark morphs of the other two species are not nearly as common (Sibley, 2nd edition).
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
The distinct falcon-like flight pattern and size relative to the gulls ruled out larger and bulkier Pomarine and smaller, tern-like Long-tailed Jaegers. Additionally, lack of double white flash ruled out Pomarine Jaeger.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
Field experience very limited. However, I have observed countless illustrations and read countless descriptions and watched many a video on jaegers.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Extensive and advanced. I have been seriously birding for about 8 years but I have been a birder for longer than that. Most of my time has been in the intermountain west, I am very familiar with the local species.
WERE PHOTO(S), VIDEO, AND/OR AUDIO OBTAINED FROM THIS SIGHTING?
Photo
Video
SUPPORTING IMAGES
SUPPORTING VIDEOS

FIRST ROUND VOTING:

Cliff Weisse
Accept

I feel the video shows characteristic peregrine-like flight style and is enough to support identification of Parasitic Jaeger.

Shirley Sturts
Accept

Well described - other two Jaegers eliminated

Dave Trochlell
Accept

I thought that the observer made a convincing case for this identification. The relative size and flight characteristics mentioned in the report were good evidence for Parasitic Jaeger.

Darren Clark
Accept

Combination of description/photos/video/ and likely species based on time of year supports Parasitic Jaeger.

Carl Lundblad
Accept

Documentation a bit rough but carefully considered, and all seems to support the identification.

Jay Carlisle
Accept

Described well and helpful photos/video

Doug Ward
Accept

Based on the description of size, structure, but particularly “falcon like” flight, believe the observer got the identification right. The video included does show these key points and was convincing enough for me to “accept” in this round.