Tuesday, Apr 23, 2024

The Mystery of Migration; How Did Birdbrains Learn to Navigate the Globe?

Imagine spending several weeks loading up on fatty foods and then walking nonstop from New York to Florida (about 1,200 miles) to spend the winter. Once there, you marry, immediately have children, fatten up again, and then return to New York for the summer. Meanwhile, your fast-track kids grow up in New York (without you), fatten up at fast food mills and, before summer gets too hot, they also walk to Florida without the apparent help of a map, road signs, a relative or even a guide (forget about GPS or Waze).

Sounds ridiculous – and for humans, of course it is, but this is representative of what millions of birds do every year.

Some of the distances traveled are unbelievable. These include the graying goose (1,800 miles), the whooper swan (1,500 miles), the bald eagle (1,800 miles), the snow goose (2,500 miles), the Eurasian crane (2,500 miles), the white stork (3,100 miles) and the bobolink (6,000 miles),

One incredible bird, however, beats them all many times over.

Birds of the Sun

The long-distance record for migration belongs to a little bird from the far north – arctic terns (Sterna paradisaea). They have been called the Birds of the Sun, because they spend more than eight months a year in the perpetual daylight of the Arctic region near the North Pole and migrate all the way down to Antarctica, near the South Pole.

Although the location of their primary nesting grounds in the north and feeding areas in the south were identified in the 1960s, the birds were impossible to track over the open sea. Then, in 2007, Carsten Egevang of the Greenland Institute of Natural Resources accurately mapped the tern’s migration by tagging them with “geo-locators” (also called “loggers”). It wasn’t easy. In the summer 2007, his team attached the 1.4-gram device onto the leg of about 50 terns. They then let the birds go, hoping they would return the next year.

In July 2008, Egevang began the seemingly impossible task of retrieving the loggers. They spent a lot of time staring up at the air at hundreds of arctic terns, hoping to find one of the tagged birds in the air and then follow it to its nest. They were looking for a small ring with a small marker. Once they spotted a tagged bird, they kept their eyes focused on it until it landed. This revealed its nest and allowed them to set a trap to capture the bird. Then they downloaded the data.

In January 2010, Egaveng published his findings. They were startling. After leaving Greenland, the birds stopped to feast for nearly a month in deep waters of the Atlantic rich with marine life. From the North Atlantic, the terns headed southeast toward the coast of Africa. When they neared the equator, they surprised Egevang by splitting their path. Half of the birds continued along the African coast while the others turned west toward Brazil. Though now separated by thousands of miles, the birds remained focused on their ultimate destination. By November, both sets arrived in Antarctica as temperatures warmed in the southern hemisphere.

In early April, now rested and refueled, the terns sensed the approach of winter and, within days, the entire population moved north. Flying almost non-stop for two months, they traveled up to 300 miles a day and arrived together at Sand Island, their original location, during the first week of June. The timing of the return was critical, for the window available to lay their eggs and raise their chicks is only about eight weeks.

By mid-August, another Arctic winter was at hand and once more these Birds of the Sun instinctively headed south. Along the way, they would again endure the challenges of distance, weather and navigation. Some arctic terns will undertake this journey 30 times during their lives.

It stretches scientific imagination how they are able to find their way so far away and then get back to exactly the same spot where they spent the summer last year. The annual round trip of the arctic tern is around 45,000 miles. If you extrapolate that throughout their life span, it adds up to about 1.5 million miles – the distance to the moon and back again three times.

If humans did that, think of the technology necessary. Picture the cockpit of an airplane perhaps. The tern not only comes ready-built with its own “cockpit,” but all the “electronics” are highly miniaturized, extremely reliable, maintenance free and easily reproduced. Furthermore, this remarkable bird needs no training. It begs the question how such amazing “equipment” could have evolved.

As amazing as the tern is, more amazing is the migration of a creature with an even smaller built-in “electronics.”

The Monarchs of Migration

The annual migration of North America’s monarch butterflies is nothing short of miraculous. Each year, up to 300 million monarchs travel more than 2,000 miles from northern America and Canada to a remote forest 200 miles west of Mexico City. They do so even though not one of them has ever made this trip before and they are on the way to an area that they have never seen. Regardless, they arrive at the same remote area high in the Mexican mountains every year at exactly the same time. It’s not only a feat of endurance and navigation unlike anything else, but one of the most profound mysteries in the natural world.

A monarch’s wingspread is 10 centimeters and it weighs half a gram. Its flight to Mexico is the equivalent of a human being circling the Earth 11 times on foot. To prepare for its epic flight, it engages its voracious appetite. As a caterpillar it eats milkweed, poisonous to every other animal including humans. A frog that tries to eat a monarch will vomit A bird will have a heart attack. But a monarch caterpillar can eat 3,000 times its weight in milkweed!

The miracle of the monarch begins in late August at a place just north of Lake Huron in Canada. The tiny caterpillar destined to become a monarch butterfly will outgrow and shed its skin four times. The fifth time the caterpillar disappears, it is transformed into a chrysalis, a delicate case within which a completely new being takes form. The caterpillar is dissolved into a stew of genes that brews up a new being. The nibbling jaws become a long tube. Twelve beady eyes meld to become two. After about ten days in the chrysalis, the new creature is complete. All traces of the caterpillar are gone and in its place is a butterfly with four delicate wings. The newly developed monarch butterfly must wait a few hours for its wings to harden before it can finally fly.

Their migration is part of an amazing, carefully timed movement that defies explanation. The mystery starts at the very beginning, because no one knows exactly what triggers the exodus from Canada. How they survive their marathon migration is another mystery. They only fly when conditions are perfect. If it’s too cold, they get sluggish and can’t flap their wings. If it’s too hot, they stop flying so they don’t get overheated. They must also stop often for nectar and water. Every time they land, they risk being eaten by predators such as spiders and praying mantises. Bad weather is also the monarch’s enemy. A rainstorm can be deadly.

If it survives predators and bad weather, a monarch that started in Canada has to fly at least 50 miles a day to get to Mexico. The physical effort this requires is remarkable for a creature so small with such fragile wings. Compounding the miracle, butterflies are the worst possible body form for trying to make a long-distance migration. Every time they flap their wings, they’re using energy at least 20 times the rate than when they’re not flapping. They’re burning their fuel at a great rate. They compensate by soaring like a glider on rising air. The sun heats the ground and the ground heats the air above it. As the air heats, it expands, becomes lighter and begins to rise. Pretty soon, a column of rising air creates conditions that allow the butterflies to maintain an altitude. It’s like a free ride. Soaring is the key for them to get to Mexico.

On the shores of the Great Lakes, just days into their journey, the monarchs face their first geographic hurdle – miles of open water and constantly shifting winds. The Great Lakes also present a barrier they can’t see across. Even with no land in sight, monarchs somehow know how to navigate in the right direction. If a headwind in the wrong direction threatens to blow them off course, they stop and wait. When they sense that the wind has shifted in their favor, they fly on.

One scientist remarked, “I’m quite frankly amazed that an insect the size of a monarch butterfly…would know enough to stop at a certain location when the winds wouldn’t be favorable and wait until they get the wind to shift in a way that’s going to help them get across a large body of water or a large area of land. It’s quite frankly amazing.”

At the University of Kansas, Chip Taylor studies the forces at work in the monarch migration. One of his tagging experiments had a surprising outcome.

“We ran some experiments a few years ago. We took butterflies from Kansas and transferred them to Washington, DC. Initially, they behaved as if they were still in Kansas. They started out flying in the same direction they would have taken to Mexico from their original home in Kansas, almost directly south. Starting from Washington, that flight path would never get them to Mexico. Amazingly, after a few days, the displaced monarchs somehow reoriented themselves and changed course to a strong southwest heading. That meant that even starting from an unfamiliar location, they still ended up in the right place in Mexico!”

Monarchs live in other parts of the world in warm climates, but only Canadian and North American monarchs migrate such an incredible distance to avoid the certain death of a cold winter. Exactly how they navigate from Canada to Mexico is an unsolved mystery to scientists. However they do it, the ultimate destination of their incredible journey is a tiny area of pine trees about 60 square miles and 10,000 feet high in the mountains of Mexico. Huddling for warmth, hoarding their energy, the monarchs cling to the pines for five months. When spring arrives, they tilt their wings to bounce sun onto their backs, warming up for flight. They’ll ride the rising summer breeze and head north. Once more, the ancient cycle will be renewed.

Nothing about a monarch makes it seem capable of its epic quest. It is truly a miraculous creature whose abilities defy explanation by ascribing it to its pinhead-sized brain.

The Mystery of Migration

How do birds make the tremendously long trip, year after year, to arrive at some faraway destination – very often at the same date and at the same exact location as the previous year? The answer isn’t simple. Indeed, it’s one of the great mysteries of modern science.

To find north, humans look to a compass. Man-made compasses work by using Earth as an enormous magnet and orienting a tiny magnet attached to a needle to the planet’s north and south poles. Some scientists speculate that birds may use an internal compass to navigate between their nesting areas and wintering grounds. Even though some research helps explain how this natural compass may work, other scientists caution that there are more pieces to the puzzle of how birds navigate on their long migrations.

“An animal that has to migrate over great distances needs to have both a compass and a map,” said biologist Cordula Mora. “If you have a compass, you know where north, south, east, [and] west [are], but you don’t know where you are, so you don’t know where you should be going.”

Robert Beason is a wildlife research biologist with the US Department of Agriculture in Sandusky, Ohio, and an expert on bird navigation. He noted that stars – not the magnetic field – may also either fully or in part provide the birds with their visual bearing. Think about that. Imagine it’s a clear night and you’re travelling along the road. Suddenly, you realize you’re lost. Lost? No problem. Just look at the stars, right? Well, when it comes to star navigation, most humans don’t know the first thing, and those who do have studied it thoroughly. How do birds with their birdbrains know?

Other scientists favor a theory that birds are tuned into polarized light. (If you don’t know what that is, you’re in good company.) Another possibility is that birds are “tuned in to the Earth’s infrared rays.” Another is that they are “tuned into slight changes in barometric pressure.”

Think about that. Science has taken centuries to develop very sophisticated technology to identify and measure things like the Earth’s magnetic field, the movement of the stars, polarized light, infrared rays and barometric pressure. Yet, long before satellites with their multi-million-dollar antennae orbiting the Earth, birds apparently knew all about these things and were using them to survive.

In truth, nobody can say for sure how they do it. And even if they did know how, science has no concrete evidence detailing the steps necessary how the ability developed.

By Chance?

A site called Evolution News analyzes and fact-checks research in scientific journals and media coverage of scientific issues. One review involved a study of migrations patterns of the European bee-eater (Merops apiaster) and its journey between Germany in summer and Angola in winter, a distance of 8,700 miles. To the researchers’ surprise, some birds separated from the main flock in small groups, flew thousands of miles apart on another route, and then re-joined the main flock up to five days later, even though the sub-flocks probably encountered different environmental conditions along the way.

The writers at Evolution News had this to say:

The wonder of this behavior can be appreciated by reversing roles. Imagine the birds running an experiment on humans. They remove all smartphones and electronic devices, outfit them with loggers the people can’t read, and send them through uncharted territory in Africa in small groups of mixed people who don’t know each other, telling them to meet in Germany. Wouldn’t the birds be flabbergasted to watch small groups split off from the main group, hike for a thousand miles on a different route without communication, and then re-join the main group a week later? Even if the humans used ultralight aircraft, it would be astonishing to see them find one another.

Try to build a robot that can fly and power itself by capturing and consuming insects. While you’re at it, make it beautiful to look at and able to sing a beautiful song. Fit all that capability into two ounces and give it software to find a target 9,000 miles away. Then endow it with the ability to make copies of itself. If you succeeded at all this, would you not be offended to hear some people say it “emerged” by chance?

(Next week, we will explore the amazing migrations of non-flying creatures.)


Better than Meteorologists’

A recent study of migrating birds adds to the notion that animals make better meteorologists than humans do. The evidence is a flock of birds that flew away from its nesting site days before there were any signs of danger and well before forecasters predicted the arrival of a massive storm system that spawned 84 confirmed tornadoes and killed at least 35 people in April 2014.

“Meteorologists were predicting that the storm might come our way,” said the study’s lead author, Henry Streby, a research fellow and visiting scholar at the University of California, Berkeley. “But by the time they were saying they were sure it was coming, the birds had already figured it out and were gone.”

The golden-winged warblers normally spend winters in South America and fly up to Tennessee to nest, Streby says. They had been at their nesting site for just a couple of days before they turned around and headed south again.

The discovery was not intended. Researchers had been testing to see if a new kind of geolocator could be carried by the tiny birds. The geolocators were a success and stayed on the warblers for a year, recording everywhere the birds went. When the researchers recaptured the birds and analyzed the location data, they were stunned to discover that the warblers had taken off from their breeding grounds in the Cumberland Mountains of eastern Tennessee, where they had only just arrived, for an unplanned migration south taking them out of the path of the oncoming storm. All told, the warblers travelled 932 miles in five days to steer clear of the tornado-producing system.

Streby suspects that the birds were alerted by low-frequency sound waves sparked by the tornadic storm. Those waves would be right in the range birds can pick up, but undetectable by human ears. “They might be able to hear the storms coming and make a decision to leave and come back rather than hunker down and try to survive the tornadoes,” he says.

Tornado expert John Allen isn’t convinced that the birds are hearing the sounds of developing whirlwinds, once more demonstrating that scientists are at a loss to pinpoint the precise nature of this ability. Though no one can say for sure how animals know a storm is brewing, “It’s clear they are better forecasters than we humans are,” Allen says.



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