Tuesday, February 14, 2012

MEET THE ALCIDS


Do you know your alcids? Most people know what gulls and terns are, and sandpipers are familiar even if the multitude of species can't be distinguished. Skimmers and skuas are less known, but it doesn't take a stretch to believe it when you learn they are related to gulls and terns. These birds are all in the same order, Charadriiformes, indicating their close relationship. But there is another group in the order that is not so obviously related to the others. These are the alcids, members of the family Alcidae.

Alcids are diving birds, much like loons and grebes and ducks in their general appearance and habits. They are relatively short-necked compared with other diving birds, so that in flight they look as much like footballs as birds. These footballs have wings, of course, but they use them not only for swimming but also for flying. Very few birds swim underwater with their wings rather than their feet, but these birds do. This method of locomotion is called wing-propelled diving.

The best-known wing-propelled divers are penguins, but they can't fly. Alcids do both, and quite well. In flight their relatively small wings keep them from soaring or gliding like a gull or turning on a dime like a sandpiper, but as long as they keep them beating at high speed they do very well in powered forward flight. When they try to turn, they slide sideways in the air before changing direction.

Wing loading is weight divided by wing area. The wing loading of these birds is very high, so they have to run along the water to take flight, into the wind whenever possible. They try to get all the lift they can, so they flatten their body and spread out their tail and webbed feet to increase the lift surface. Sometimes they splash along the surface before actually getting airborne.

Four species of alcids are common in Puget Sound, and all are fish-eaters. Common Murres and Rhinoceros Auklets breed widely in large colonies, the murres on cliff ledges and the auklets in burrows they dig. Both species are present in the Sound primarily in winter, but the auklets breed as close as Protection Island, and many forage in the northern part of the Sound during that period.

Both of these species are adapted to go where the fish are, and as schools of herring and sand lance are local and on the move, the birds adopt the same strategy. In an area with currents, diving birds commonly float downcurrent through areas rich in marine life, often around upwellings, feed as they can, then fly upcurrent to make the same journey again. Obviously these activities change with the changing of the tides, and they can be seen best in rich areas with powerful tide exchange such as Admiralty Inlet.

Marbled Murrelets feed in the same areas and even on the same fishes, but they are much less common. That species is unique in being a forest breeder. Pairs remain together throughout the year, then fly into old-growth forests in the spring to nest on a branch high in a big Douglas-fir. Because they use old growth, their populations have declined greatly in historic times.

Pigeon Guillemots breed locally in the sound, either in holes they dig at the tops of banks or in crevices under docks. They feed primarily on bottom fishes such as sculpins and gunnels, and they are the only one of the group that uses their feet as well as their wings as paddles as they move slowly over the bottom searching for prey.

The alcids are characteristic and charismatic birds of Pacific Northwest marine environments, and ferry travel is a good way to see them. Spend time at and especially on Puget Sound and learn about them for yourself.

Dennis Paulson









1 comment:

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