Flights of the Albatross

The wandering albatross (Diomedea exulans) flies extraordinarily long distances in search of food. Riding the wind on long, thin, rigidly outstretched wings, it skirts the waves as it glides for hours over the ocean surface. Its white plumage, white beak, black wing tips, and wingspan of eleven feet or more make the wandering albatross a dramatic sight in the sky.

Wandering albatross. JJ Harrison

Truly a world traveler, this seabird regularly circles the globe at southern latitudes, plunging into the sea to scoop up squid and fish along the way and sometimes following cruise ships and other vessels to pick up scraps thrown overboard. In one week, it can travel thousands of kilometers on a single foray to gather food for its baby chick.

Biologists at the British Antarctic Survey have investigated the role of seabirds and seals as the top predators in the marine food web of the southern ocean. Their long-term goal is to assess the impact of these animals on the ecosystem.

As one component of this effort, biologist Peter Prince and his coworkers equipped wandering albatrosses with electronic recorders or radio transmitters for satellite tracking to determine the birds' foraging behavior and identify patterns in the way they search for food.

In one experiment, the researchers attached electronic activity recorders to the legs of five adult birds, who made 19 separate foraging trips. The devices recorded the number of 15-second intervals in each hour during which the bird was wet for 9 seconds or longer. The wet periods indicated interruptions in a bird's flight path when it alighted on the water to eat or rest.

To cope with the large quantity of data generated by such studies, the biologists enlisted the aid of a team of physicists to identify patterns in the way albatrosses search for food. According to the analysis performed by the physicists, the data showed that the flight patterns of wandering albatrosses—as they fly, settle on the sea, then fly off again—fit the type of random motion characteristic of a Lévy flight (see "Galaxies and Coffee Cups"), in which the birds make long journeys interspersed with short foraging flights clustered in a small area.

Ecologists speculated that the flight patterns of the wandering albatross had evolved to exploit the patchy distribution of fish and squid, which may reflect the distribution of plankton in the restless ocean, and this patchwork in turn may arise from ocean turbulence effects.

Such patterns may also occur in other biological systems. Some scientists have suggested that Lévy random walks and Lévy statistics may apply to the behavior of ants and bees, but the evidence remains spotty. Others have studied the possible uses of these models in physiology and medicine, including the characteristics of heartbeat rhythms and the branched structure of the lung's airways.

It's possible that in biological systems there's an evolutionary advantage to behaving according to Lévy statistics. Because the environment appears to be fractal, an organism that behaves fractally can better take advantage of such patchy opportunities. For the wandering albatross, this means wide-ranging, stop-and-go searches for food that may be unpredictably scattered across the ocean.

"Newtonian physics began with an attempt to make precise predictions about natural phenomena, predictions that could be accurately checked by observation and experiment," physicist Michael Shlesinger and two colleagues noted in a 1996 essay titled "Beyond Brownian Motion." The physicists further explained, "The goal was to understand nature as a deterministic, 'clockwork' universe."

The application of probability to physics developed much more slowly, the authors contended. The earliest uses of probability were in characterizing data—how the average represented the most probable value in a series of repeated measurements, and how the various measured values fitted the familiar bell-shaped curve of a Gaussian (or normal) distribution.

In the nineteenth century, such distributions also came to represent the behavior of molecules in a gas. In constant motion, molecules repeatedly collide and change speeds. At a given temperature at any moment, however, the largest number of molecules travel at a well-defined characteristic speed, and the distribution of speeds among all the molecules fits a specific type of curve.

Thinking about random walks ("Walking Wild I") and Brownian motion ("Quivering Particles I"), about Lévy flights and chaos, and about Markov processes and fractals means tangling with the complex interplay of pattern and randomness in nature and in human activity.

It's no simple matter to analyze phenomena that change randomly and uncontrollably from moment to moment, whether those changes are physical, biological, or mathematical. Making such efforts, however, begins to cast light on the essence of life, which seems to teeter far out of equilibrium and perpetually on the brink of randomness.