Laurence A. Marschall
Nature's Compass: The Mystery of Animal Navigationby James L. Gould
We know that animals cross miles of water, land, and sky with pinpoint precision on a daily basis. But it is only in recent years that scientists have learned how these astounding feats of navigation are actually accomplished. With colorful and thorough detail, Nature's Compass explores the remarkable methods by which animals find their way both near home/i>
We know that animals cross miles of water, land, and sky with pinpoint precision on a daily basis. But it is only in recent years that scientists have learned how these astounding feats of navigation are actually accomplished. With colorful and thorough detail, Nature's Compass explores the remarkable methods by which animals find their way both near home and around the globe. Noted biologist James Gould and popular science writer Carol Gould delve into the elegant strategies and fail-safe backup systems, the invisible sensitivities and mysterious forces, and incredible mental abilities used by familiar and rare species, as they investigate a multitude of navigation strategies, from the simple to the astonishing.
The Goulds discuss how animals navigate, without instruments and training, at a level far beyond human talents. They explain how animals measure time and show how the fragile monarch butterfly employs an internal clock, calendar, compass, and map to commence and measure the two-thousand-mile annual journey to Mexico--all with a brain that weighs only a few thousandths of an ounce. They look at honey bees and how they rely on the sun and mental maps to locate landmarks such as nests and flowers. And they examine whether long-distance migrants, such as the homing pigeon, depend on a global positioning system to let them know where they are. Ultimately, the authors ask if the disruption of migratory paths through habitat destruction and global warming is affecting and endangering animal species.
Providing a comprehensive picture of animal navigation and migration, Nature's Compass decodes the mysteries of this extraordinary aspect of natural behavior.
Laurence A. Marschall
Barbara J. King
"Though animals are the book's stars, animal-navigation scientists come a close second. The innovation and sometimes pure cheek of experiments contrived to learn about nature's compasses are fun to read about."Barbara J. King,Times Literary Supplement
"What the Goulds have written is both an absorbing tale of biological discovery and a tantalizing scientific cliffhanger."Laurence A. Marschall, Natural History
"Nature's Compass provides a wonderful account of efforts to unravel the mysteries of animal migration. Effectively drawing on their own experiences and the extensive scientific literature in the field, the Goulds explain what we currently know about how animals locate their positions. Their survey also offers an accessible starting point for those who might wish to improve our understanding of the topic."Homare Yamahachi, Science
"James L. Gould and science writer Carol Gould explain the amazing ways in which animals orient themselves and make their way through the world. Scientist James details biology experiments that reveal how animals measure time, locate landmarks, and direct themselves across the globe, while writer Carol eloquently shows readers the beauty of the monarch butterfly's trip across the United States and into Mexico, the complex dance of honey bees, and homing pigeons' internal GPS system. Throughout the book, the authors combine their strengths to demonstrate both the scientific wonder and beauty of the internal compasses in animals. With an eye toward larger issues, the Goulds also examine the ways in which global warming and habitat destruction affect and endanger these magnificent and complex animals. . . . Recommended."Susan E. Brazer, Library Journal
"Nature's Compass: The Mystery of Animal Navigation is an excellent resource for interested arm-chair ecologists and also undergraduate students who wish to understand the scientific history of analysis of how animal navigation occurs. At the same time, Nature's Compass: The Mystery of Animal Navigation is also an excellent book describing how sometimes it is difficult for Home sapiens to accept the cognitive intelligence and capacity of others who reside in our animal kingdom even when we are presented with the bare facts supporting these obvious assertions."Gabriel Thoumi, MongaBay.com
"Research on animal navigation sits at the interface of physics, biology, and many different cultures, and has seen many heated debates, past and present. Nature's Compass is an excellent introduction to the field and hopefully will serve as inspiration for new research. . . . I found it enjoyable and would recommended it to anyone interested in the subject."Anders Hedenström, Times Higher Education
"This scholarly and engaging book is the first in more than twenty years to summarize for the layman the latest research on the wonders of animal navigation. . . . Comprehensive and fascinating, the book cites extensive research, including a significant amount conducted by the authors themselves. While illuminating, the book also raises many questions that it cannot yet answer. We have much to learn from these wondrous creatures but, as this book makes clear, much of their mystery remains."Kristen Rabe, Foreword Reviews
"Nature's Compass is as much about navigation as it is about animals' abilities to navigate. Biologist James Gould and science writer Carol Gould fully describe the information needed for navigation, accurately pointing out that this applies equally to a diversity of organisms ranging from butterflies to humans. Their description serves the work well since readers gain an appreciation of the challenges and mysteries surrounding animal navigation. . . . Overall, this is a fascinating treatment of animal navigation. Readers will gain insight into how animals manage to navigate in three dimensions, including a profound appreciation of their ability to 'solve' complex problems."Choice
"While this is certainly a book for birders, beekeepers, and lovers of the natural world, it's also a book for sailors, pilots, and anyone who has ever had trouble finding their car in the parking lot."Susan Meadows, Santa Fe New Mexican
"I found this to be an enjoyable and informative read. I would recommend it to any biologist interested in animal navigation and I would make it part of any curious student's reading list."Verner P. Bingman, Quarterly Review of Biology
Read an Excerpt
The Mystery of Animal Navigation
By James L. Gould, Carol Grant Gould
PRINCETON UNIVERSITY PRESSCopyright © 2012 Princeton University Press
All rights reserved.
Navigating — Problems and Strategies
* Devil Birds of the Atlantic
It was a navigator's worst nightmare. Shortly after midnight on a cloudy September night in the middle of the North Atlantic, the ship was suddenly attacked. Out of nowhere the screeching and wailing ghosts of long-dead sailors swept through the rigging, terrifying the superstitious seamen and drowning the captain's shouted orders. The panicking crew knew instantly that they had trespassed on the infamous Isles of Devils, haunted by the souls of the thousands of crewmen who had perished on the treacherous shoals. But by the navigator's reckoning, they were far to the west of the legendary death trap.
Within minutes, though, over the din came the fatal sound of waves breaking on a lee shore to the east. Turning the ship and piling on sail was their final mistake: the keel ran hard into one of the lethal coral reefs that ring the islands. The ship sank almost immediately, joining countless others that had suffered the same fate in that graveyard of the Atlantic that is the Bermudas. What had gone wrong?
Long-distance navigation is a life or death challenge for many nonhuman animals as well; the difference is that they know what they are doing. Few sights are more impressive to earthbound people than an isolated formation of geese passing overhead on their way to distant summer or wintering grounds. Theirs is not a journey on a wing and a prayer: all but first-year birds have a detailed map of the route in their brains, complete with remembered landmarks for piloting. After dark in the spring and fall literally billions of songbirds traverse the skies each night unseen, often to destinations hundreds or thousands of miles away. Unlike waterfowl, these passerines are using multiple compasses and a mystical GPS sense to find their way. At least 30 species would have been passing overhead on that fatal night in the Atlantic, maintaining their steady course for 2300 miles from Nova Scotia to South America.
Animals were on the move in the surrounding waters of the North Atlantic as well, racing against time to reach new habitats as the seasons changed. Humpback whales migrate past Bermuda on thousand-mile journeys with maps and compasses adapted to the gloom of the ocean. Many fish and sea turtles are similarly equipped for equally monumental seasonal redeployments. Below them on the seafloor spiny lobsters prance in tandem lines on arduous journeys, knowing their location in the cold darkness to within a few feet.
On a more local scale, honey bees and many other insects on the Bermuda islands, as elsewhere, commute scores of times each day from home to sources of food, water, or building materials, using a series of backup compasses and learned landmarks. Relative to their small body size and myopic vision, these trips are nearly as epic as those of geese, and each journey is a life-or-death event. Nesting birds on this mid-Atlantic refuge log many hundreds of miles shuttling back and forth first to collect nest material and then food for their young; getting lost would mean starvation for the next generation. Mice do much the same on the ground, but must employ a different set of cues and processing strategies more suited to running mazes than finding distant continents. Monarch butterflies flutter 2000 miles south from the United States and Canada to a remote mountain peak in Mexico, orienting by the ever-moving sun and a mysterious sense of location.
Faced with what is to us an alien task in an unforgiving world, humans stand in awe of the judgment and precision with which animals use cues — often undetectable by us — that are frequently ambiguous and ephemeral. We must depend on luck as much as talent, trying with clumsy approximations to replicate the compass sense that animals use innately to work out the rules of piloting and mapping, and to pinpoint our position on the globe without the seemingly magical combination of sensory abilities and inborn processing circuits that for other species comes as standard equipment. The navigators whose ships came to grief on Bermuda's reefs were, in fact, employing an amalgamation of generally reliable animal strategies. What went wrong for that ill-fated ship beset by devils?
When Fernandino deVerar set sail in his well-armed, two-masted, 300-ton Portuguese merchant ship San Antonio in 1621, he understood the risks. He had sailed that spring from Cadiz in southwestern Spain for Cartagena in what is now northern Colombia with a load of goods for the American colonies. Like all human navigators of the time he was unable to judge his east–west position (the longitude) when out of sight of charted land, so his ship had sailed south with the northern coast of Africa clearly visible to larboard (the left, or port, side of the ship). He had abandoned this piloting strategy once his collection of instruments, charts, tables, and measurements of the sun's elevation combined to tell him he was 12° north of the equator — roughly the latitude of his destination 3000 miles on the other side of the Atlantic. Then deVerar had turned west and, using a magnetic compass, sailed along this latitude until he reached the Caribbean. This vector strategy is similar to the way many migrant songbirds navigate their first season, before they learn enough to plot routes that incorporate the subtle realities of spherical geometry.
Going south before "westing" to the New World allowed sailors to take advantage of the trade winds, which blow generally from the northeast in the northern tropics. The resulting "broad reach," with the breeze coming diagonally from behind, extracts the maximum force from the wind. The ocean current at this latitude, part of the North Atlantic gyre, also provides a welcome two-mile-an-hour push to the west. Hundreds of species of migrating birds, sea turtles, and fish also know how to take advantage of these winds and currents.
The problem for sailors came with the return journey, their ships laden with treasure looted from Mexico and Peru. September is the height of the hurricane season in the Atlantic; the San Antonio, one of many vessels waiting in Cartagena, did not load her share of the booty until late August. It was a rich haul: thousands of hides, 6000 pounds of indigo, 30,000 pounds of tobacco, 5000 pounds of sarsaparilla, and 5000 English pounds worth of gold and silver. But there was not a moment to lose before bad weather set in.
Unfortunately deVerar and his convoy could not simply sail back east; that would take them into the teeth of the wind and current. Without wings or fins to propel them, they instead had to return to the gyre and sail north amid often contrary winds, piloting their way through the islands of the West Indies. The captain's plan was to use his magnetic compass in a two-step strategy of vector navigation. The compass would allow him to bear north to the latitude of Cadiz and then (resetting his course to the east) let the westerlies and the gyre carry him across the Atlantic. As the San Antonio left the last of the well-charted Caribbean islands behind and plunged north toward her turning point at 36.5° north latitude, she necessarily lost track of her exact position.
The convoy depended on occasional sightings of the sun and stars for latitude; for longitude they had to rely on dead reckoning, a common procedure used by animals that we will look at in detail presently. This all-too-appropriately named strategy keeps track of approximate headings and speeds and times (with, in the case of humans, nothing more sophisticated than a compass, a knotted rope, and an hourglass), and then attempts to reconstruct location by integrating over the various legs of the journey. As with any bird or fish in the same situation, small errors in judging distance, direction, time, or velocity inevitably accumulate, making the resulting estimate ever less accurate. And once out of sight of land there is no way to factor in the drift induced by currents or wind. A sideways drift alters the actual direction traveled; a drift along the axis of travel — equivalent to a headwind or tailwind while flying — changes the distance covered.
The part of the gyre they were in as they left the Caribbean is notoriously unreliable. They might be in the center of the flow, being carried north or northeast at 3 mph; they might be a bit to the east in the Sargasso Sea, the huge calm eye of the gyre; or they might be in the Gulf Stream, which peels off unpredictably to the NE, warming Europe as it carries tropical waters to the British Isles. To make matters worse, the convoy was racing before a tropical storm, and had gone without a sighting of the sun or stars for some days.
By the first hours of September 12 deVerar's ship was at 32.3° latitude, about 250 miles south of their intended right turn. Unaware of the branch current that was propelling the ship and with no celestial sightings (the clouds hid the first-quarter moon, which in any event had set at midnight), the navigator's dead reckoning placed them about 50 miles south of his actual position — a harmless enough mistake on its own. The rest of the convoy, scatted by the storm, was about 20 miles behind and slightly to the west. Unfortunately, the San Antonio and the other ships also had drifted about 100 miles east of the northerly track they were trying to maintain, carried by a warm offshoot of the Gulf Stream. The tide was at its highest about 2 a.m., just covering the treacherous reefs.
Just ahead, the "devils" had taken wing about three hours earlier. Nocturnal gadfly petrels known as cahows spend their nights flying low over the water in search of squid, punctuating their hunting with loud, eerie screeching. The lights aboard the San Antonio had drawn them like moths as the ship pushed blindly NNE, just to the west of the islands that were home to the seabird colony. The terror inspired by the unearthly shrieking of the birds combined with the navigational incompetence of her human pilots and the shortcomings of their instruments to doom the ship.
Unlike the sailors, the cahows are superb navigators. They seem to know their longitude to within a mile and their latitude with even better precision, clouds or no clouds. Their internal compasses are far more reliable than anything the hand of man could produce at the time. The islands were the birds' breeding grounds; this was their one landmark in a sea empty for hundreds of miles, a beacon of safety rather than danger. And the cahows are by no means exceptional. The ocean around Bermuda is full of equally adept navigators, many of which know just where they are at any given moment. Green and loggerhead sea turtles, white-tailed tropicbirds, American eels, yellow-fin tuna, and humpback whales — none of these animal navigators are in danger of losing track of their position for long. Only our species earns this dubious distinction.
An animal's ability to know its location and the direction of its goal is one of the greatest mysteries of science. Increasingly, though much remains to be discovered and understood, this ability seems less magical. Some of the mysteries are merely products of our opposing desires to romanticize behaviors on the one hand and oversimplify them on the other, and thus to look in the wrong places for answers. We also are prone to anthropomorphize, imagining that animals see challenges in the same way we do and use the same strategies to solve the problems they encounter. As a result, we have often overlooked some surprising alternative approaches that make complex tasks much simpler for well-programmed animals. In particular, we have assumed that our fellow creatures cannot measure orientation parameters any more accurately than human instrumentation, and ought in fact to do less well than our elaborate and expensive equipment.
Our plan is to look briefly at the range of orientation strategies evident in animals, from the simple to the astonishing. Because an essential component of many of these strategies is the ability to measure periods and intervals, we will examine time sense. The next most basic component is an array of alternative compasses to orient movement. We will then look at how time and compasses combine with memory to permit piloting and inertial navigation. This will lead us to the greatest challenge to human understanding, the map sense. With a fuller picture of how animals navigate, we will conclude with the imminent threats humans pose to navigators: habitat destruction and climate change.
As we will see, understanding animal navigation is often critical to conservation, and the recent gigantic steps in decoding the workings of the compass and map sense have come not a moment too soon. Consider the plight of the cahows, whose superb navigational skill and unearthly voices proved no defense against hungry colonists or their rats, cats, and rooting hogs.
The wholesale slaughter of the birds continued despite one of the earliest efforts at conservation, a 17th-century edict by the governor against the "spoyle and havocke of the Cohowes." They were thought to be extinct on the mainland by the late 1620s, less than 20 years after the islands were first settled.
After more than three centuries with no confirmed sightings, however, 18 nesting pairs were discovered on a small, inhospitable islet on the southern fringe of Bermuda in 1951. None of their young survived that year, decimated by rough weather, competing tropicbirds, and scavenging rats. After an intensive breeding effort there are now 250 individuals, their survival dependent on dedicated conservationists who transfer the chicks painstakingly to handmade burrows on larger islands.
Our knowledge of the cahow's behavior, and particularly the way the chicks imprint on the location of their burrows and the coordinates of their particular tiny island, is still a bit sketchy. Each pair lays only one egg. Several nights after its parents leave for the open ocean the fledged but inexperienced chick walks out of its burrow to the edge of a nearby cliff, looks at the stars overhead, makes some mental measurements (probably of magnetic field strength and inclination), spreads its wings, and plunges into the dark to take up its destiny as a wandering seabird. Without specialized instruments, charts, or tables, the cahow depends day after day on its innate ability to orient and navigate the North Atlantic. Five years later each steers its way back to Bermuda to breed. How do they do it?
* Getting Warmer
Cahows are, to be sure, pushing the limits of evolutionary technology. For most species of navigators and migrants the challenges are less extreme, though every bit as important. Sightless coral larvae spawned on the reefs just off Bermuda must make their way up near (but not too near) the surface at the right time of day to avoid predatory reef fish, feed for a few weeks, and then return to the reefs to find a suitable place to settle and start growing. Bacteria, protozoans, and plankton that inhabit the island soil and the inshore waters also move up and down, responding to cues that indicate danger or safety, food or toxins, forever improving on their location as best they can in a changing world. The bees tirelessly carrying pollen and nectar from the island's semitropical vegetation back to their hives are among the most elegant navigators on the planet.
To combat what he saw as an anti-intellectual wave of anthropomorphism in animal psychology, the 19th-century psychologist C. Lloyd Morgan asserted that when multiple theories compete, the explanation that introduces the fewest steps is likely to be the best. The sensible injunction to researchers to account for an animal's behavior in the simplest possible manner is known as Morgan's Canon. In the first half of the 20th century behaviorists even used this mantra to account for human behavior entirely in terms of conditioned responses to stimuli.
Because animals were seen as little more than machines, researchers invoked the canon to explain navigation and migration in terms of automatic responses to immediate environmental cues. Whether in bees or bacteria, petrels or protozoa, much of orientation and navigation is based ultimately on a limited set of sensory cues and processing tricks. But while these strategies are largely inborn, it does not follow that they are simple.
Zooplankton, the minute drifting organisms in the sea that ultimately feed nearly all of the ocean's fish, migrate down daily and back up at night. The logic of this redeployment is simple. Their prey — the photosynthetic bacteria, protists, and algae collectively known as phytoplankton, or drifting plants — are near the surface around the clock. But the many fish with excellent vision that eat the zooplankton are generally diurnal, active during the day. For copepods and other zooplankton, dining on phytoplankton at night and plunging into the relative safety of the depths during the day makes perfect sense.
The massive migration of zooplankton has been simplistically explained as an alternation between an aversion to light when the sun is available, and a balancing aversion to gravity when the sun is not present. In fact, however, the zooplankton begin their journeys before light levels change, actually anticipating dawn and dusk.
While much of animal (and human) behavior is in fact rooted in relatively simple responses, navigational abilities typically depend on sophisticated processing as well as multiple sensory and endogenous (internal) inputs. Even with microorganisms, for instance, something far more interesting than simple reactions is going on. Zooplankton moved from the ocean to a darkened aquarium still redeploy down in the daytime and up at night, at least for a few days. This surprising persistence of vertical movement is not based on some trick for sensing the sun through solid walls; instead the organisms have a 24-hour timer that has "learned" which are the daytime hours and which are associated with night. The rhythm persists in constant light or dark. The internal timer, not the appearance and disappearance of the cues, controls the creature's response preferences. Shift dawn artificially by a few hours and plankton experience jet lag, only slowly getting back into phase with the sun.
Excerpted from Nature's Compass by James L. Gould, Carol Grant Gould. Copyright © 2012 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Meet the Author
James L. Gould is professor of ecology and evolutionary biology at Princeton University. Carol Grant Gould is a science writer who has published widely. Together, the Goulds have written nine earlier books, including The Animal Mind and Animal Architects.
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