Rare Bird Report 43-B-08

Parasitic Jaeger (Stercorarius parasiticus)
American Falls Reservoir
4 Oct 2008

Observers: Linda Mack & Scott Barnes

Field Encounter: Mack picked up a dark bird with a fast flight style and angular wings that we believed to be a jaeger, mostly based on previous experience with this genus.  We viewed the bird in binoculars as it moved northward from our viewpoint at the boat ramp at the southwest corner of the reservoir.  Later, we relocated the bird from a bluff about a half mile north along the western shore.  There we were able to view the bird in flight and compare it with flying Ring-billed Gulls and Bonaparte’s Gulls for size reference through scopes (Swarovski 20-60 and Nikon 38x).  The bird spent time flying around and floating the water for periods of time.  Eventually we lost the bird amidst the hordes of Ring-billed Gulls and other waterbirds present.

Description: floating on the water’s surface at a distance, we were able to see a dark brown bird with a warm yellowish-brown hind collar.  In flight the bird showed white flashes in the primaries and a wing-width (at base) not longer than the tail.  General behavior/GISS was of a dark and falcon-like bird in flight; powerful with fast movements; angular wings; size smaller than Ring-billed Gulls that were nearby in flight.

Similar Species: our identification was largely based on size, shape, structure, and comparative experience with all three jaegers.  Given the comparative views with nearby flying Ring-billed Gulls (larger), Bonaparte’s Gulls, and Common Terns (the latter noticeably smaller) we felt confident that the bird was a Parasitic Jaeger.  Long-tailed Jaeger would be smaller and more daintily-built—more along the size of a Common Tern or Bonaparte’s Gull, further the bird did not show a tail length longer than the wing length at the base and we felt the white visible in the primaries at this distance was too extensive; conversely the bird we saw was not big enough (in comparison with nearby Ring-billed Gulls) or heavily-built (bulky chest and very broad wings longer than the tail) for a Pomarine Jaeger. 

Previous Experience: both observers have seen many Parasitic Jaegers of various morphs and ages in our home state of NJ (from shore and on pelagic trips), as well as pelagic trips in Massachusetts, North Carolina, and California.  Similarly, both observers have experience with Pomarine and Long-tailed Jaegers from many pelagic trips off NJ, NC, and CA.

Scott Barnes

Senior Naturalist

Sandy Hook Bird Observatory/New Jersey Audubon Society

scott.barnes@njaudubon.org (work)

myiarchus16@yahoo.com (personal)