Weidensaul, Scott. Living On the Wind: Across the Hemisphere With Migratory Birds. North Point Press: New York, 1999.
The evolutionary fabric of life, adapting to gradual geological and climatic circumstance over slow eons, is visited in the daily revelations that come from a careful observation of living things. Perhaps the most easily observed of natural creations (besides our ever abundant fellow hominids) are those found in the class Aves, a flowing tapestry of genetic flux reaching back to that deified moment when bipedal carnivorous dinosaurs converted scales into feathers and flew away from the sprawling chaos of the post-apocalyptic late Jurassic world.
For a growing number of Americans there is little that compares to the subjective thrill of viewing animals—particularly birds—in what is left of the wild. In fact the money spent on wildlife observation, a “hobby” (some would say obsession) that is the fastest-growing outdoor leisure activity in the United States, makes it the top-ranking pastime in America in terms of dollars spent toward gratification. And birds are so pliant to our whims: many species will come to our prepared feeders and accept as nesting grounds the meager woodlots interspersed between our expanding housing developments. Oftentimes we tend to take them for granted. But the familiar songbirds we see cracking black-oil sunflower seeds outside our windows have within them a legacy of seasonal wanderlust that continues to astound scientists with its meticulous exactitude, heroic effort and awesome persistence. Those fantastically colored wood warblers, orioles and tanagers that greet us each spring in a multihued circus of tropical delight are products of a ruthless winnowing over evolutionary time, perfected by millennia of combating storms and starvation to ensure the survival of their kind. The shorebirds that to us appear bizarre in shape and purpose as they dig and probe their way along the tideline are genetic realizations of flying mastery and endurance, animals whose physiology and unfathomable sense of direction has been honed through epochal accretions of knowledge—knowledge of the atmosphere, of the seasons, of the swelling curvature of the planet itself. For migrating birds the planet is big, but it is comprehensible.
Scott Weidensaul’s Living on the Wind, like the volume reviewed previously in these pages, does much to help us understand and appreciate natural phenomena, and his tale is told in a compelling and vibrant manner throughout. Bird migration is still not fully understood by the ornithological community, but Weidensaul allows us to savor the experience of not knowing to its fullest degree; indeed, the singular ability of entire species to undertake mass movements across continents to arrive at a precise destination appeals to our sense of the wonderful and the sublime. Like quantum physics and the new reaches of astronomy, certain aspects of the living world are imbued with an incontestably spiritual aura.
Among the few objective certainties that we can use to comprehend bird migration, Weidensaul points us to recent discoveries such as crystals of magnetite that are found in the nasal cavities of certain bird species, including the bobolink and pintail duck, as well as in honeybees and other organisms that depend upon a long-range, geometric sense of direction. But opinion is divided as to whether it is the earth’s magnetic field or the changing pattern of constellations (most bird species migrate at night) that ultimately directs the traveling flocks: “more recently, the consensus has been that birds use the navigational clues available to them in a hierarchy, with visual guideposts like the sun and stars a clear favorite.” Again pushing the limits of the miraculous—like rumbling whalesong that may be heard from across the globe—birds “can detect infrasound, extremely low-frequency waves of the sort generated by wind, ocean surf, volcanic eruptions, earthquake tremors, and thunderstorms, and which can travel for hundreds or thousands of miles. In theory, at least, a bird migrating down the Great Plains can keep the sound of the Atlantic in one ear and the Pacific in the other, and thus stay on course.” Who would ever have reckoned the ubiquitous American robin (Turdus migratorious) to be possessed of such godlike senses?
Just why do birds migrate? Competition is the short answer; birds migrate into areas where their fellows are fewer in number and the food is more plentiful. A munificent availability of food means a heightened chance of breeding success, and the continuation of the species is of course the oldest and strongest drive of all, even if playing the odds means twice-yearly travel from the Aleutian chain off Alaska to Tasmania (bar-tailed godwit) or east Africa (northern wheatear) or Patagonia (American golden-plover). But what about the yearlong residents of these places? How do seasonal migrants keep from competing directly with the locals, thereby negating any nutritional advantage of migration? Two scientists that Weidensaul accompanies in Panama offer an explanation: “They found that the migrants (thrushes, warblers and flycatchers) focused their attention on two main kinds of food—hard-shelled insects like ants and beetles or invertebrates like millipedes and termites that produce toxic chemicals.” These food sources are thought to be of lower nutritional value than the caterpillars and spiders that the native birds primarily hunt; the thrushes also partook of fruits that ripened at the time of their arrival. The scientists therefore “found very little overlap between the diets of migrants and residents but quite a bit of competition between migrants of the same ‘guilds’—ecological shorthand for groups of species with similar feeding techniques, like foliage-gleaning insectivores.” Nobody said it was going to be easy.
The physical demands of long-range migration are extreme indeed: “a Kentucky warbler flying 600 miles across the Gulf [of Mexico] will use four or five grams [of fat] on its nonstop flight, arriving up to 35 percent lighter than when it took off.” Strong headwinds can add considerably to the stresses of migration, and chance storms can wipe out hundreds of thousands of birds at a stroke. When the passage has been especially difficult, the starving arrivals rely completely on the availability of intact coastal habitat in which to find ready protein; it is the increasing destruction of such ecosystems along the Gulf and both oceanic coasts that has contributed to the desperate waning of Neotropical species, birds like warblers, thrushes and tanagers that spend much of their lives in the humid rainforests and riverine jungles of South and Central America but breed in the United States.
Living On the Wind is a boon to those seeking a highly readable collection of data illuminating the biannual wonder of bird migration; it is also a testament to the fragile grace of the creation we in our aggressive ignorance threaten with destruction. Once again the enduring North Point Press format is aesthetically pleasing and sturdily designed, with thorough notes and bibliographic references.
The evolutionary fabric of life, adapting to gradual geological and climatic circumstance over slow eons, is visited in the daily revelations that come from a careful observation of living things. Perhaps the most easily observed of natural creations (besides our ever abundant fellow hominids) are those found in the class Aves, a flowing tapestry of genetic flux reaching back to that deified moment when bipedal carnivorous dinosaurs converted scales into feathers and flew away from the sprawling chaos of the post-apocalyptic late Jurassic world.
For a growing number of Americans there is little that compares to the subjective thrill of viewing animals—particularly birds—in what is left of the wild. In fact the money spent on wildlife observation, a “hobby” (some would say obsession) that is the fastest-growing outdoor leisure activity in the United States, makes it the top-ranking pastime in America in terms of dollars spent toward gratification. And birds are so pliant to our whims: many species will come to our prepared feeders and accept as nesting grounds the meager woodlots interspersed between our expanding housing developments. Oftentimes we tend to take them for granted. But the familiar songbirds we see cracking black-oil sunflower seeds outside our windows have within them a legacy of seasonal wanderlust that continues to astound scientists with its meticulous exactitude, heroic effort and awesome persistence. Those fantastically colored wood warblers, orioles and tanagers that greet us each spring in a multihued circus of tropical delight are products of a ruthless winnowing over evolutionary time, perfected by millennia of combating storms and starvation to ensure the survival of their kind. The shorebirds that to us appear bizarre in shape and purpose as they dig and probe their way along the tideline are genetic realizations of flying mastery and endurance, animals whose physiology and unfathomable sense of direction has been honed through epochal accretions of knowledge—knowledge of the atmosphere, of the seasons, of the swelling curvature of the planet itself. For migrating birds the planet is big, but it is comprehensible.
Scott Weidensaul’s Living on the Wind, like the volume reviewed previously in these pages, does much to help us understand and appreciate natural phenomena, and his tale is told in a compelling and vibrant manner throughout. Bird migration is still not fully understood by the ornithological community, but Weidensaul allows us to savor the experience of not knowing to its fullest degree; indeed, the singular ability of entire species to undertake mass movements across continents to arrive at a precise destination appeals to our sense of the wonderful and the sublime. Like quantum physics and the new reaches of astronomy, certain aspects of the living world are imbued with an incontestably spiritual aura.
Among the few objective certainties that we can use to comprehend bird migration, Weidensaul points us to recent discoveries such as crystals of magnetite that are found in the nasal cavities of certain bird species, including the bobolink and pintail duck, as well as in honeybees and other organisms that depend upon a long-range, geometric sense of direction. But opinion is divided as to whether it is the earth’s magnetic field or the changing pattern of constellations (most bird species migrate at night) that ultimately directs the traveling flocks: “more recently, the consensus has been that birds use the navigational clues available to them in a hierarchy, with visual guideposts like the sun and stars a clear favorite.” Again pushing the limits of the miraculous—like rumbling whalesong that may be heard from across the globe—birds “can detect infrasound, extremely low-frequency waves of the sort generated by wind, ocean surf, volcanic eruptions, earthquake tremors, and thunderstorms, and which can travel for hundreds or thousands of miles. In theory, at least, a bird migrating down the Great Plains can keep the sound of the Atlantic in one ear and the Pacific in the other, and thus stay on course.” Who would ever have reckoned the ubiquitous American robin (Turdus migratorious) to be possessed of such godlike senses?
Just why do birds migrate? Competition is the short answer; birds migrate into areas where their fellows are fewer in number and the food is more plentiful. A munificent availability of food means a heightened chance of breeding success, and the continuation of the species is of course the oldest and strongest drive of all, even if playing the odds means twice-yearly travel from the Aleutian chain off Alaska to Tasmania (bar-tailed godwit) or east Africa (northern wheatear) or Patagonia (American golden-plover). But what about the yearlong residents of these places? How do seasonal migrants keep from competing directly with the locals, thereby negating any nutritional advantage of migration? Two scientists that Weidensaul accompanies in Panama offer an explanation: “They found that the migrants (thrushes, warblers and flycatchers) focused their attention on two main kinds of food—hard-shelled insects like ants and beetles or invertebrates like millipedes and termites that produce toxic chemicals.” These food sources are thought to be of lower nutritional value than the caterpillars and spiders that the native birds primarily hunt; the thrushes also partook of fruits that ripened at the time of their arrival. The scientists therefore “found very little overlap between the diets of migrants and residents but quite a bit of competition between migrants of the same ‘guilds’—ecological shorthand for groups of species with similar feeding techniques, like foliage-gleaning insectivores.” Nobody said it was going to be easy.
The physical demands of long-range migration are extreme indeed: “a Kentucky warbler flying 600 miles across the Gulf [of Mexico] will use four or five grams [of fat] on its nonstop flight, arriving up to 35 percent lighter than when it took off.” Strong headwinds can add considerably to the stresses of migration, and chance storms can wipe out hundreds of thousands of birds at a stroke. When the passage has been especially difficult, the starving arrivals rely completely on the availability of intact coastal habitat in which to find ready protein; it is the increasing destruction of such ecosystems along the Gulf and both oceanic coasts that has contributed to the desperate waning of Neotropical species, birds like warblers, thrushes and tanagers that spend much of their lives in the humid rainforests and riverine jungles of South and Central America but breed in the United States.
Living On the Wind is a boon to those seeking a highly readable collection of data illuminating the biannual wonder of bird migration; it is also a testament to the fragile grace of the creation we in our aggressive ignorance threaten with destruction. Once again the enduring North Point Press format is aesthetically pleasing and sturdily designed, with thorough notes and bibliographic references.
