BIRDS OF NANTUCKET

This week's bird is a parasite - at least that's what its name implies. The dictionary tells us a parasite is something that lives off the work of other creatures and does nothing for them in return. In ancient Greece the term referred to a "professional dinner guest." Both these terms approach the reality of this animal.

Let's look at the scientific name - Stercorarius parasiticus. The first word means "having to do with dung." The second one recites the parasite theme. We're not climbing higher on the popularity scale, are we?

The full name of this bird is the Parasitic Jaeger. The "J" is pronounced like a "Y." Jaeger is a word that originated in Holland, meaning hunter. My reference says the word "yacht" has the same origin. I'll let you chew on that for a moment. It's ironic that in Europe, where the word jaeger originated, birds of this group are called "skuas," a word from the Faroe Islands, halfway between Iceland and Scotland. In Europe, they call the Parasitic Jaeger the Arctic Skua. I'm sure that somewhere the bird-mavens are arguing about this even as I am writing.

There are three species of jaegers, the Long-tailed, the Pomarine, and this week's bird, the Parasitic. The Long-tailed is considered "accidental" here with only three records within the last 50 years. Both the Pomarine and Parasitic are "uncommon" at this time of year. They are tricky to tell apart since most seen here are not in adult plumage. The bird books make distinguishing them look easy because of the difference in their tails. Indeed, the Eskimos use this trick, calling them "knives, forks, and spoons," but they see adult birds in breeding plumage. We'll discuss the cutlery rules later on.

Jaegers are dark, hawk-like sea birds the size of a small gull. Like birds of prey, they have color phases from almost black all over to lighter colored with white bellies. Most of the jaegers we see are light-phased birds. If you see one that appears white from the throat on down, you have a Parasitic. Pomarines always show a dark band across the upper breast. Young birds of both species are mainly brown, but Parasitics look more mottled. Parasitic Jaegers are also slimmer and more long-winged in flight.

We see them in ones and twos along our ocean beaches where there are large flocks of gulls and terns. What you notice first is a disruption of the flock as a darker bird sweeps through. Their intent is to make any bird panic and drop whatever food it's caught. Many times an individual bird will be pursued until it drops or actually regurgitates what it has just swallowed. The jaeger then swoops down to claim its prize before it reaches the water.

Parasitic Jaegers are found all around the world. They nest in the high Arctic across Alaska, Northern Canada, and Greenland. Also they are found in Scandinavia and Arctic Russia. Their nests are simple scrapes on the ground, flimsily lined with grass or lichens. They lay two eggs and spend the summer purloining eggs from the myriad of bird species also nesting on the tundra, as well as snatching their young.

Like many arctic nesting species young jaegers are fed to the point where they outweigh their parents and are literally too fat to fly. The adults solve this problem by heading south, leaving the youngsters to trim down and get into the air. Any adult birds seen here are usually in August and September. At this time of the year, this year's new crop of jaegers is making its first trip south. Most of them stay at the fringes of visibility off our eastern shores but sometimes come into Nantucket Sound with a northeast storm.

Birds passing here now will spend their winter at sea from the waters off southern Florida all the way south to the Straits of Magellan at the southern tip of South America. Jaegers can swim so they can rest and feed on the water's surface. When not harassing gulls and terns, they pick up decaying matter from the water's surface, tying them to their "dung" connection.

In May and June they wing their way past Nantucket again. The best chance to see them over the next few weeks is to watch for action around the big flocks of the delicate Bonaparte's Gulls that will be congregating near Codfish Park and Low Beach.

Oh - and regarding the cutlery reference. Adult Long-tailed Jaegers have marvelously long central tail feathers, making up as much as one third of their length. They are the knives. Pomarine Jaegers have shorter central tail feathers, the ends of which rotate 90 degrees. These are the spoons. And this week's Parasitic Jaeger adults have shorter but very pointy central tail feathers, the forks. I

George C. West creates illustrations for these articles.

If you enjoy "social" birding, join the Nantucket Bird Club for a walk any Sunday starting at 8 a.m. in the Nantucket High School parking lot. Dress for the weather. Plan to be out until about 10:30 a.m. and perhaps meet for breakfast afterwards.

To hear about rare birds, or to leave a bird report call the Massachusetts Audubon hot line at 1-781-259-8805.