Bird Lore: Parasitic Jaeger

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Jaegers and their close relatives the skuas are both scavengers and predators in the marine world. The Parasitic Jaeger, often called the falcon-like jaeger, is a September-October visitor to Puget Sound while on its way to its wintering waters of Mexico, Central America and the Caribbean. In Edmonds, the public pier and Sunset Avenue are good locations to look for the Parasitic Jaeger as it harasses gulls and terns for the fish they forage.

To the casual observer, the Parasitic Jaeger looks like a dark gull. It is distinguished from the dark Heermann’s Gull, with which it overlaps on the waterfront, by the white flashes on the upper and under sides of the wing tips, seen in flight. It is a fast flier that engages in acrobatic pursuit, often twisting upward as it chases down gulls and other seabirds in pursuit of food. You can see the white flashes of the wing tips as this jaeger chases a gull for its food: https://www.youtube.com/watch?v=557W8YbVlQQ. This is a one-minute video of a jaeger chasing a gull or tern: https://www.youtube.com/watch?v=zpmWlfQ5tMI.

The Parasitic Jaeger spends most of its life at sea, mostly over the continental shelf and within a few miles of land. At sea and at its coastal nesting grounds, its diet is mostly fish stolen from other birds. On land it will eat small birds and their eggs, rodents, insects and berries. This jaeger is named for the two main strategies it uses to forage. Parasitic refers to its habit of pursuing gulls and terns, forcing them to drop their food. Jaeger comes from the German word for hunter, as this bird at times will prey on small mammals, eggs and small birds.

An Arctic breeder, the Parasitic Jaeger prefers open country such as tundra, but also breeds on rocky barrens and at coastal marshes. It first breeds at 4-5 years of age. It is flexible in that it will breed both in isolated pairs and in colonies. Pairs or groups will perform acrobatic display flights. Other courtship displays include upright posturing, calling, and the male feeding the female.

The male selects a nest site on the ground in the open. The nest, built by the female, is nothing more than a shallow depression with a sparse lining of plant materials. Both sexes incubate the two eggs for about 25-28 days. Downy young will leave the nest a few days after hatching but will remain near it. Both adults feed the young by regurgitation. Young birds are 25-30 days of age at first flight. They will remain with the adults for a few more weeks.

The global population of the Parasitic Jaeger is estimated at 3.5 million. For conservation purposes the species is considered to be of low concern. Most of its breeding range is remote from human disturbance and there has been no evidence of major changes in the population. In the 1800s, populations in Scotland declined because of shooting. Gamekeepers thought that the Parasitic Jaeger caused a decline in the numbers of gamebirds. In the 1900s, Baltic Sea populations declined due to human destruction of nests. The apparent reason was an aversion to this bird’s predatory habits.

Calls from a pair of birds near their nest can be heard here: https://www.xeno-canto.org/203452.

— By Carol Riddell

Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.

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