Beak of the Week – Pomarine Jaeger

The Pomarine Jaeger is a rare and fascinating seabird, the largest of the three jaegers. Field identification of jaegers can be difficult due to the high variation in their populations; however, Pomarine Jaegers are the most barrel-chested of the jaegers and have the most obvious “wing flash” created by the white bases of the primaries near the tip of the wings. Pomarine Jaegers also have thick bills, and adults sometimes display two long, half-twisted tail feathers. Jaegers can be separated from gulls and terns from a distance by their large size, brown appearance, and kleptoparasitic behavior against other bird species. Pomarine Jaegers will sometimes tackle and harass gulls and terns to steal their food, though they don’t rely on this strategy as much as the Parasitic Jaeger. 

Pomarine Jaeger reproduction depends entirely on the availability of brown and Arctic lemmings in their Arctic breeding grounds. Reproduction is typically only successful once every three or four years and is coupled with the lemming population. However, in years with fewer lemmings, jaegers will hunt more shorebirds and eggs to compensate. Adults capture lemmings by spotting them from a perch or the air and use only their beaks to catch their prey. Pomarine Jaegers will also form foraging groups with other individuals and dig lemmings out of their burrows using their bills. Pomarine Jaegers are socially monogamous, and both parents assist with raising the young. On years with lots of lemmings, two eggs are laid in a slight depression in mid-June and hatch early-mid July. Each parent develops two brood patches on their underside and takes turns incubating the eggs. The young are fed pieces of lemming until fledging. Jaegers are nomadic when not breeding and can be found over the ocean in both the northern and southern hemispheres. 

Pomarine Jaegers can occasionally be seen flying far out over the ocean from the Bolivar Flats Shorebird Sanctuary. One was recently photographed loafing on the beach there, so keep your binoculars focused on the ocean; eventually, you will see one of these fantastic birds!