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The Albatross Conundrum

Common sense tells us that the albatross should not survive. After all, it builds its nest hundreds and sometimes thousands of miles from where it feeds. In human terms that's like owning a house in New York but shopping for groceries in Japan. Yet somehow the albatross makes these bizarre logistics work.

First, a few albatross basics. An oceanic bird, the albatross spends most of its life far from land. It feeds primarily on fish and squid on the open ocean, killing these creatures near the water's surface. It also will eat dead animals that it finds floating in the water, and some albatross species have been known to follow ships and feed on refuse thrown overboard.

The only time an adult albatross comes ashore is to nest. A female will lay one egg each year, usually on a remote island, then both parents will take turns incubating the egg and minding the chick once it hatches. But unlike other birds that share parenting duties, a shift at the nest for an albatross can last a week or more. While its mate travels in search of food, the albatross sits and waits . . . and waits . . . and waits. How can it survive without food for a week? How does the chick survive without fresh food after it hatches? And, most perplexing, how does the bird that's looking for food continue to fly for days on end without running out of energy?

One answer is that the albatross's digestive tract functions differently than those in most birds. In essence, it stores the food consumed in different chambers. The first chamber, called the proventriculus, houses liquid fats -- the gastrointestinal equivalent of long-term storage -- while water, proteins, and other non-fat particles continue on to the remainder of the digestive tract. These latter substances provide immediate fuel for the albatross, and their quick absorption frees up space for additional food to be consumed and more fat stored before the bird returns home.

It's the stored fat that powers the bird between food runs. Whenever the albatross needs a boost it allows a small portion of this liquid fat to pass from its proventriculus to the rest of its digestive tract. And since fat packs more calories per ounce than other foods, what's inside the proventriculus can sustain the bird weeks. There's even enough for the chick when it hatches. All the parent has to do is regurgitate some of the fat, then pass it to the chick from beak to beak.

As for how the albatross flies such long distances without using up all its fuel, the answer is that it doesn't flap its wings to fly like other birds. Instead, the albatross soars for most of its journey by taking advantage of subtle and not-so-subtle differences in wind direction and wind speed over the ocean. Scientists call the process dynamic soaring, and at its most basic it requires the bird to alternate between downwind gliding and cross-wind gliding. In other words, the albatross zigzags to its destination -- not the fastest route, to be sure, but the one that conserves the most fuel.