Pomarine Jaeger
Pomarine Jaeger
Stercorarius pomarinus
At a Glance
Powerful and fast-flying, a predator and pirate of the ocean and the far north. The largest of the three jaeger species. Not seen from shore as often as Parasitic Jaeger, but usually the one seen in greatest numbers on boat trips offshore. In northern Alaska, this is a major predator on the brown lemming: During summers when these rodents are in low numbers, many Pomarine Jaegers do not attempt to nest.
All bird guide text and rangemaps adapted from by Kenn Kaufman漏 1996, used by permission of Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Category
Gull-like Birds, Gulls and Terns
IUCN Status
Least Concern
Habitat
Coasts and Shorelines, Lakes, Ponds, and Rivers, Open Ocean, Tundra and Boreal Habitats
Region
Alaska and The North, California, Eastern Canada, Florida, Great Lakes, Mid Atlantic, New England, Northwest, Plains, Southeast, Texas, Western Canada
Behavior
Direct Flight
Population
1.100.000
Range & Identification
Migration & Range Maps
Most migration is offshore. Migrates later in fall than other jaegers, especially young birds, with juveniles rarely seen south of the Arctic before October. Some apparently migrate to far southern oceans, but others remain off North American coasts in winter. Very rare inland, but such strays may appear in summer as well as during migration seasons.
Description
22" (56 cm). Adult has wide, blunt-tipped central tail feathers. Pattern of underparts highly variable: white, dark, heavily barred, often with dark chest band. Looks heavy-billed, very black on head. Juvenile in first fall usually dark brown with buff barring. Later immature stages quite variable.
Size
About the size of a Crow, About the size of a Mallard or Herring Gull
Color
Black, Brown, White, Yellow
Wing Shape
Broad, Pointed, Tapered
Tail Shape
Long, Pointed, Square-tipped, Wedge-shaped
Songs and Calls
Harsh chattering calls; a harsh which-yew.
Call Pattern
Falling, Flat, Rising, Undulating
Call Type
Odd, Scream
Habitat
Open sea, coasts (offshore); tundra (summer). Spends most of year at sea, often over continental shelf, but usually stays farther from land than Parasitic Jaeger and may occur far out in mid-ocean. Concentrates over upwellings and boundaries of currents. In summer on tundra, generally low-lying areas near coast.
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Behavior
Eggs
2, rarely 1-3. Olive to brown, blotched with dark brown. Incubation is by both parents, 25-27 days.
Young
May leave nest a few days after hatching, but remain in general area, are fed by both parents. Age at first flight about 31-27 days; dependent on parents at least 2 more weeks.
Feeding Behavior
Forages at sea by dipping to surface in flight to catch fish, by catching small birds in flight, also by harassing other birds and forcing them to drop their food. Forages over land mostly by hovering and dropping on prey.
Diet
Includes fish, rodents, birds. Diet varies with location. At sea, usually eats fish, also smaller birds and some carrion or refuse. Breeding birds feed heavily on lemmings and other rodents; non-breeding birds in summer around tundra have more varied diet, including birds, eggs, fish, carrion, insects.
Nesting
At least in some regions, much more likely to nest in years when rodent populations are high. Birds younger than 4-5 years old attempt nesting only in such good seasons. Defends nesting territory against other species of jaegers. In courtship, members of pair face each other, vibrating wings and calling. Male may feed female. Nest site is on open ground, sometimes on slightly raised ridge or hummock. Nest (built by both sexes) a shallow depression, often lined with bits of plant material.
Climate Vulnerability
Conservation Status
Local breeding numbers fluctuate strongly along with population cycles of lemmings and other rodents. Worldwide jaeger population difficult to monitor, but no evidence of major declines. Most of breeding range is remote from impacts of human activity.
Climate Threats Facing the Pomarine Jaeger
Choose a temperature scenario below to see which threats will affect this species as warming increases. The same climate change-driven threats that put birds at risk will affect other wildlife and people, too.