Pirates of the High Seas

     He was an opportunist, a professional marauder. He took risks and was comfortable in his skin, for larceny was in his DNA. Sweeping low across the waves with steady wingbeats, his dark eyes searched for easy “marks” among the terns and gulls that were dipping and diving on a school of anchovies. His streamlined body and tapered, falcon-like wings enabled him to reach high speeds and change directions fast: useful skills for an avian terrorist, a pirate of the high seas: a parasitic jaeger. Suddenly, he swerved into a flock of elegant terns, barely avoiding several mid-air collisions, isolating a tern that had just seized a good-sized fish. He harassed it mercilessly, the terrified “host” zig-zagging repeatedly, but clearly no match for its attacker. It surrendered its catch and fled. The triumphant jaeger snatched it up, then soared aloft, giving a vigorous full-body shrug, so each of its feathers fell back into pre-scuffle place. Grooming is important, even for pirates.

     Feathered Freebooters: Parasitic jaegers, Stercorarius parasiticus, regularly feed in the food-rich waters of Greater Farallones National Marine Sanctuary and adjacent waters. These large, dark, gull-like birds demonstrate a distinctive seasonally-split personality: on their summer breeding grounds they are true to their namesake “jaeger”–German for hunter— preying directly on shorebirds, songbirds, waterfowl, and their eggs, with some rodents, berries and carrion for variety. But in fall, winter and spring at sea they become shameless “kleptoparasites,” pilfering prey from their fellow seabirds.

     Parasitic Parenting: Parasitic jaegers nest in circumpolar tundra habitats, near coasts or rivers. Mated pairs form long term bonds; they create a nest – a simple depression on a slight rise, pressing moss and lichens into a lining.  One to three eggs are laid, the downy chicks hatching after a month and are tended for a further month until ready to fledge, though they sometimes linger (Gen-Xers, or millennials?). Breeding over, the adults go their separate ways back to sea, but return the next year to reclaim both nest and mate. Young non-breeding birds may remain at sea two or more years before ever returning to land.

     Stalking The Stalker: Jaegers are visitors to California waters each spring and fall, feeding to build strength and stamina during their epic migration. Fall sea conditions off our coast are often calmer than in spring, making whale watch or pelagic birding day-cruises more comfortable. As to singling them out from other seabirds, their habitats and habits are a dead giveaway. Parasitic jaegers prefer ocean waters over the Continental Shelf, out to about 50 miles, but can be found nearer shore, and in estuaries, even at river mouths. To look for jaegers, just look for trouble: a very fidgety seabird flock, or a dark, powerful bird in a high-speed chase with an erratically flying gull or tern desperate to escape flyway robbery.

     Global Paracitizens: Parasitic jaegers are found in all ocean basins. From their Arctic breeding grounds, our local stock migrates to the Southern Hemisphere, arriving in October and November, and feeding in the South Pacific and Southern Oceans, off South America and eastern Australia. They embark the following February and March on their journey home.

     Parasitic jaegers are protected by the Migratory Bird Treaty Act, and their numbers worldwide are stable, due to the remoteness of their Arctic breeding grounds. Much of their West Coast feeding range is protected through national marine sanctuary designation, which helps ensure the health and bounty of the seas that sustain them. 

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For more information on the sanctuary’s seabird research, education and resource protection, see https://farallones.noaa.gov/eco/seabird/, and https://farallones.noaa.gov/science/access.html