With the 26th annual Kachemak Bay Shorebird Festival just having wrapped up, it’s a good time to contemplate the mystery of migration. Come spring, with clockwork regularity, billions of birds embark on their journeys northbound to mate and rear young.
Using their reserves of fat like gasoline, migrating birds fuel up before departure, some flying nonstop across oceans spanning thousands of miles. To put it into perspective, these oceanic pilgrimages have been described as the equivalent of a human running 12,000 consecutive four minute miles. Western sandpipers, one of the most common birds spotted during the Shorebird Festival, migrate from as far away as South America to breed on the arctic tundra of Alaska.
Not only is this feat of endurance impressive in itself, the various species of birds often arrive within a few yards of the precise locations they were born or nested in the year before. Our feathered friends amaze us; where is their compass, where is their map?
From ancient mythology to modern scientific inquiry, avian migration has always been difficult to observe, and comical hypotheses have emerged over history. In ancient Greece, Aristotle reported the annual movements of birds to warmer climes, but he also reported that some birds hibernated in riverbank mud or transformed into other species.
The ancient notion that storks bring babies is likely rooted in their migration and roosting habits, the storks arriving and breeding in springtime. As classicist Richard Armstrong notes, in medieval Europe the explanation for barnacle geese appearing in late winter was that they grew on trees, and the Roman author, Pliny the Elder, wrote that flocks of migrating quails could sink ships by landing on their sails at night.
With the clear knowledge of foresight, bird enthusiasts can look back at these notions as fanciful. Yet they underscore how deeply humans desire to understand. Much of avian life was ultimately unknowable, so people filled the gaps with stories and beliefs.
The turning point in migration theory came in 1822, when a German hunter happened to shoot down a stork with an arrow in its neck. The arrow was determined to be from Africa, providing the most striking evidence that birds traveled thousands of miles. From this starting point, countless studies have been conducted to unravel the mystery of migration.
To terrestrial humans, a tiny songbird’s migration of thousands of miles might seem extreme, mysterious. The evolution of the migratory trait could be a response to one of the most lasting and dependable features of the Earth: seasonal change. Predictable and yearly changes such as monsoon rains, insect hatches, fruiting of trees and spring growth are all cyclical, providing dependable food resources at different times of year in different regions. The rich breeding grounds of the Yukon-Kuskokwim Delta and Arctic Coast — the ultimate destination for many Alaska-bound shorebirds — is a cornucopia of food for forage. Birds also stop along the way to refuel in the Copper River Delta and here in Homer. Migratory birds have evolved over millennia to adapt to the seasonality of the planet.
The next question that arises, then, is how do birds unerringly find their way to these food sources?
The aerodynamics of birds in flight, using motor and sensory cues, is incredibly complicated; scientists from biology and quantum physics still struggle to understand the complexity. The ornithologist Ronald Lockley’s famous 1950s study highlighted just how little we know about homing. In his study, he placed a Manx shearwater from its home in Wales and placed it in a covered box on a flight to Boston. Once released, the bird reoriented itself from its rather rude departure, headed East over Boston Harbor, and was back in its own burrow in Wales in a mere 12 days, baffling the scientists. Migrating birds seem to have an inherent consciousness of the magnetic topology of the Earth, the workings of which is hard to pin down.
Often flying at night, according to a recent National Geographic article, they are thought to recognize patterns of stars and the tilt and rotation of the night sky, as well as being able to attune to the earth’s magnetic field. For most creatures capable of orienting themselves with respect to magnetic fields, a mineral called magnetite is thought to be the major sensory agent.
According to a 1993 New York Times article by Malcolm W. Browne, researchers also believe that migrating birds can visualize a dark polarized band in the sky 90 degrees from the sun. The tilt of this band, which is invisible to human eyes, is hypothesized to inform the bird of the position of the sun and therefore his orientation on earth.
But magnetite and polarized light bands can’t explain homing entirely. Like many features of nature, the migratory ability is emergent: arising out of sensory cues of many different sources working together. It’s a synergistic quality, this homing instinct, using a myriad of sensory cues ranging from the stars and sun to magnetic and gravitational fields to the topography of the land itself.
An interconnected system, such as a flock of birds, is more than the sum of its parts. Chelsea Wald notes in a January 2014 article in Nature how studies on flight precision amaze scientists; recent research has shown birds utilize energy saving formations in flight, flapping their wings in sync with the bird directly in front of them to reduce wind resistance. This requires an almost preternatural awareness of not only themselves in space, but also their orientation to the wing flaps of the bird in front of them. In these precision flights, each individual is exquisitely attuned to its position in the overall hierarchy of the structure, like a network of individuals forming one conscious unit. Dragonflies, tuna, salmon, ants and bees do this too.
What’s amazing is that these minerals and visual abilities are imbedded in their very brains, allowing them to orient themselves towards a larger celestial body seemingly without effort.
Any talk of migration wouldn’t be complete without mentioning landscape change. Habitat loss severely threatens the success of migratory journeys. Since it’s such an arduous yet delicate mission, a lack of stopover points or feeding grounds can mean death for migrating birds. And these tiny birds, far from frivolous in their fragile and delicate beauty, hold entire ecosystems together: they keep insect populations under control, and are responsible for pollination and seed dispersal of countless plants. It would be a very different world without birds.
While people build rockets to the moon, a godwit accomplishes a similar feat using its evolutionary instinct. Soaring above humanity, one thing is clear; so much about migration is still an abiding mystery.