Foundations of the Eart: Global Ecological Change and the Book of Job

Along the shoreline in the Torres Islands,1 Vanuatu (the archipelago nation formerly known as the New Hebrides), a medium-sized gray sandpiper appears on the beaches in October. It is the tuwiä, or, in English, the wandering tattler (Tringa incanus), a migratory bird that breeds in the summer along the alpine mountain streams of Siberia, Alaska, and northwestern Canada. In the nonbreeding season, it migrates and eventually circumnavigates the Pacific.² It pushes southward down the edge of the Pacific Rim. Then it crosses the Pacific Ocean, arriving at the Hawaiian Islands in August, Samoa in August, Fiji by late August, and the Torres Islands in October.

When the Melanesian yam farmers of the Torres Islands see the tuwiä on their shore, they sing to it, “‘Tuwiä, tuwiä, nút mad gor? [Tuwiä, tuwiä, has the Palolo worm come yet?]” The head-bobbing behavior of the birds is taken to mean “Yes,” and it signals that the seas will soon swarm with the tasty segments of Palolo sea worms (Palola viridis). The Palolo worm is a reef creature about twenty-five centimeters long. Two times a year, on the days of the waning quarter of the moon in October and November, the Palolo sheds its rear segments, which float to the surface and emit sperm and eggs.³ The seas can be full of these worm segments, which are harvested with baskets woven specially for the occasion. Locally, the worms are considered a delicacy. Palolo feasts bring people together and set the stage for annual planting and harvest times. The tuwiä is the harbinger of the Palolo worms and of the agricultural lifecycle. When harvesting the first fruits of the yam crop, the farmer sings, “May the mena⁴ of the tuwiä give the people much food.” Mena (or, more generally, mana in several Polynesian languages across Oceania) is a term that on the Torres Islands means “capacity” and refers to the capability to evoke transformative forces inherent in the living world.⁵

This example from remote islands located between the Coral Sea and the South Pacific may seem jarringly unfamiliar to the Western observer, but it has direct similarities to the manner by which familiar religious celebrations such as Easter, Passover, or Ramadan are determined. The Palolo worm and the tuwiä combine the two aspects of the Joban whirlwind questions cited for this chapter: knowing the ordinances of the heavens and knowing the cycles of nature.

Neolithic cultures depend upon their agricultural productivity for survival. Knowing when to plant crops is and was essential to their success and sustenance. If one knew that the year had about 365 days, then one could simply count the days to know when to plant. This would provide an approximate solar-based calendar. Unfortunately, difficult challenges hide in understanding the “ordinances of the heavens.” The year is not exactly 365 days long. The time it takes for the Earth to revolve around the Sun, based on a fixed reference such as a star (a sidereal year), is 365 days, six hours, nine minutes, and 9.76 seconds. If the Earth’s orbit-based year is measured as the time between equinoxes or solstices (the tropical year), the slight shift in the Earth’s orbit, called precession, produces an average year of about 365 days, five hours, forty-eight minutes, and forty-five seconds. A heliacal year is the interval of time between the rising of a star. If the star is the star Sirius, the brightest star in the sky, the year is called a Sothic year. These are also affected by precession. There are Gaussian years, Besselian years, Draconic years…While this may enrich the reader’s ability to solve really hard crossword puzzles, one should stop here.

The Islamic calendar is a lunar calendar. Each month starts with the sighting of the first crescent of a new moon. The moon-based year in the Islamic calendar, as well as other lunar calendars, is a bit less than eleven days shorter than the solar year. For this reason, Islamic holy days, such as Ramadan, migrate throughout the seasons over time.

Similarly, the Borana people of northern Kenya and southern Ethiopia calculate a lunar-month calendar to time agricultural activities and religious events.6 The Ayantu, who are experts on the observation of the sky, regulate the Borana calendar by adding an extra month about once every three years. The Ayantu make their calendric alteration based on the rise of different clusters of stars (constellations) above the horizon in relation to the rising of the moon.⁷

Easter is also a “moveable feast” based on modifying moon calendars to reset their drift against the solar calendar. The result is called a lunisolar calendar. In Western churches, Easter is observed on the first Sunday after the full moon that occurs on or after the spring equinox, which is fixed as March 21.⁸

Boranas, Jews, and Christians are, in these examples, all using the astronomical observations of the sun, stars, and moon to correct a lunar calendar so that it remains close to an annual calendar or to constrain important dates from drifting through the year. Just as the arrival of the spring equinox resets a moon calendar to pin the date of Easter as occurring sometime between the dates of March 22 to April 25, the arrival of the wandering tattler and the spawning of the Palolo worms reset the lunar harvest calendar in the Torres Islands.

The Neolithic world bristles with monumental architecture, some of which are thought to be used to observe and commemorate the ordinances of the heavens. The collection of striking and ancient architecture from the earliest times of the invention of agriculture and even earlier are found in disparate locations: Mayan ruins in Central America, Incan high-altitude cities in the Andes, stone circles in Europe, and prehistoric temples from Mediterranean islands.⁹ Machu Picchu, Chichen Itza, the Ring of Brodgar, and other similar places are simultaneously mystical and compelling. One’s imagination races to understand the almost tactile impact of these places. Perhaps it is the magic that seems to reside there that inspires the development of the various pseudoscientific explanations of their intent.

The term “archaeoastronomy,” the interdisciplinary study of astronomy and anthropology, was first used in a paper by Elizabeth Chesley Baity in 1973.¹⁰ The scale of her review paper is epic. It has 867 references to previous work, comments from nineteen other researchers (of the fifty to whom she sent advance copies of the paper), and her responses and/or rebuttals to these comments. Sponsored by the International Union of Astronomers, archaeoastronomers attended an initial successful conference at Oxford in 1982 and since that time have had several subsequent “Oxford” conferences at different locations around the world.¹¹ The Ninth “Oxford” International Symposium on Archaeoastronomy met in January 2011 in Lima, Peru. There is also a scholarly journal, Archaeoastronomy. Needless to say, scientifically rigorous archaeoastronomers are plagued by popularizations that range from highly speculative assertions to pure lunacy.

One of the more challenging aspects of interpreting the alignment of megaliths and monuments is that in the deeper past the apparent locations of rising and setting stars and other celestial events were different from today. The Earth wobbles on its axis over very long intervals, on the order of 26,000 years. This wobble is caused by interactions in the gravitational pull of the Sun and the Moon on the Earth’s bulge at the equator. Any star directly over the northern axis is a pole star, which currently is the star Polaris in the constellation Ursa Minor (the Little Dipper). Polaris would have also been the pole star 26,000 years ago. Halfway between these two times, 13,000 years ago, the star at the imaginary point in the sky above the North Pole would have been Vega, in the constellation Lyra. Vega would have been a great pole star: it is the second brightest star in the northern sky. For archaeologists, what this means is that one does not simply stroll into an archaeoastronomical site and start siting lines to star-related positions. One must know the time the feature was constructed and then compute the correction for the wobble or, as it is technically known, “precession.”

Recently, the International Council on Monuments and Sites (ICOMOS) and the International Astronomical Union compiled a list of significant heritage sites (and objects from them) for astronomy and archaeoastronomy worldwide.12 A sampling of these locations and artifacts provides at least a glimmer of the sorts of astronomical knowledge acquired by Paleolithic and Neolithic people:

2. The Thaïs bone—a piece of bone, a bovine rib, excavated from Thaïs cave (Saint Nazaire en Royans, France) in 1968–1969. The bone dates from 12000 bp and is engraved on both sides. On one side there are seven long lines scratched into the bone, with perpendicular cross-hatchings across these lines. The Thaïs bone documents the existence of a calendar system based on the phases of the moon with a seasonal factor provided by observing the solar solstices.¹⁴

3. Stonehenge World Heritage Site—an extended set of monuments (Stonehenge, Avebury, Durrington Walls, etc.) along with over seven hundred archaeological features located in the county of Wiltshire, in the United Kingdom. Construction at Stonehenge appears to have initially begun with the digging of three pits with timber posts around 8000 BCE. Around 3000 BCE, a ditch and bank were dug, and “blue-stones” from distances as much as 240 kilometers away were added, as were “sarsens,” more-local stones weighing up to forty metric tons. All of the main monuments in the larger area and Stonehenge itself have astronomical features.¹⁵ Stonehenge aligns with the solar solstices, as do several of the other monuments in the vicinity. Archaeological evidence on the timing of feasts and the solstice-aligned avenue at nearby Durrington Walls implies interpretations involving seasonal processions and rituals.

4. Chichen Itza, Yucatan, Mexico—a regional civic and religiousceremonial center as early as the sixth century CE. Its peak was in the Mayan Late Classic and the Terminal Classic periods, roughly the tenth and eleventh centuries CE. A civil war caused a decline after 1221 CE. The site is filled with ornately decorated large monuments with astronomical capabilities. Examples of archaeoastronomical features include El Castillo, or the Temple of Kukulcan, which displays light and shadow at the solar equinox; El Caracol, with several astronomical features such as solar solstice sunset alignments, the northernmost setting position of Venus, sunset at the equinoxes, sunsets on April 29 and August 13 and others; The Great Ball Court or Temples of the Jaguar, which points to the sunsets on April 29 and August 13; Las Monjas, decorated with images of the Mayan zodiac; the Temple of Venus, which has eight solar years (or five Venus cycles) represented by decorative icons; and many others.

Tupaia, according to journals of both Cook and Banks, knew the location of the ship at sea and of future landfalls far better than the Europeans. In December 1770, just eighteen months after he joined the voyage of discovery, Tupaia died in Batavia (modern Jakarta, on the island of Java). He left two copies of a remarkable chart of the Pacific Islands centered on Tahiti and showing many islands strewn over a 4,200-kilometer span of the Pacific Ocean.¹⁸ His chart is not a conventional map. It illustrates headings to Pacific Islands based on a star compass and the distance in terms of time sailing.¹⁹ Also shown are positions of shipwrecked European vessels.²⁰ One chart was owned by Richard Pickersgill, an officer who had sailed both with Cook on the Endeavour and with Captain Samuel Wallis, the discoverer of Tahiti in 1767. It is now lost. The one surviving copy, once the property of Sir Joseph Banks, resides in the British Library.

Polynesian navigation involves dead reckoning (estimation of how far a vessel has traveled at sea) and the use of stars as a compass. Since the stars and their constellations rise and set at the same location when one is on the Equator,²¹ one can determine the heading from one location to another from the stars. Studies on the Caroline Islands found that indigenous navigators and their “star compasses” involve the navigator memorizing the relative rising and setting positions of about fifteen stars.²² At any time or place, the navigator observes the stars that are near the horizon and then “imagines” the rest that cannot be seen below the horizon.

These navigation methods are augmented by the ability to detect islands that are over the horizon by observations of the flight paths of birds and from patterns of sea waves. A device designed to read the complexities of wave patterns, a Micronesian example of a navigation stick chart from the Marshall Islands (Ratak Chain, Wotje Atoll), is illustrated at the beginning of this chapter. This particular example was collected in 1960. Several of these charts are shown in different ethnographic papers over the past hundred years,23 for example, the 1899 Smithsonian Report.²⁴ Navigation stick charts augment the teaching of how one interprets the positions of distant islands using complex variations in the regular patterns of waves. They use the “swell,” the rhythmic waves produced by storms and winds that can travel long distances over the oceans.²⁵ Go to a beach: one can watch swells; they generate the rhythm of the waves. When the swells interact with islands and shallow water they can bend and travel in different directions. Marshallese navigators observe these patterns by observing and feeling the ocean’s waves slapping against the hulls of their boats. To detect the wave patterns generated by distant islands, they lie against the hulls in their dugouts and feel the small vibrations.²⁶ The Marshallese likely had navigational skill beyond that of their first European contacts.

Similarly, there is a certain irony that Tupaia’s navigational capabilities seemed on a par or better than those of Cook, particularly given that the mission of the HMS Endeavour on this voyage was to make astronomical observations intended to improve the ability of European navigators to determine longitude.²⁷ Their navigation skills gave the Polynesians the remarkable capability to travel and populate the vastest region of any peoples on Earth.

There are a thousand other facts of this kind and the same Nature has also bestowed upon many animals as well, the faculty of observing the heavens, and of presaging the winds, rains, and tempests, each in its own peculiar way. It would be an endless labour to enumerate them all; just as much as it would be to point out the relation of each to man. For, in fact, they warn us of danger, not only by their fibres and their entrails, to which a large portion of mankind attach the greatest faith, but by other kinds of warnings as well. When a building is about to fall down, all the mice desert it before-hand, and the spiders with their webs are the first to drop. Divination from birds has been made a science among the Romans, and the college of its priests is looked upon as peculiarly sacred. In Thrace, when all parts are covered with ice, the foxes are consulted, an animal which, in other respects, is baneful from its craftiness. It has been observed, that this animal applies its ear to the ice, for the purpose of testing its thickness; hence it is, that the inhabitants will never cross frozen rivers and lakes until the foxes have passed over them and returned.28

Some auguries work in one location but not at all in another. The American robin (Turdus migratorius) is a year-round resident in the American South but is the harbinger of spring in the northern United States and Canada.29 A century ago in Quebec, the first robin was thought to bring good crops and good luck on whomever’s farm it nested.³⁰ Perhaps an indication of the desire to see the end of winter here in Virginia, one often hears, “I’ve seen a robin, so spring must be coming soon.” One might think that the perceived value of auguries would depend upon their predictive capability, but evaluating how good an augury is in its predictions may be a more complex task than it might appear at first. For robin watchers in the South, if one senses the lengthening of days, knows the date, and is ready to see the end of winter, then one notices the “first” robin whether they have been around, unnoticed, all winter long or not.

In some quixotic cases, auguries may “work” by not being predictive at all. The use of bird auguries has been described for several different tribes in Borneo and especially for the Kantu’ people of West Kalimantan.31 The Kantu’ cultivate dry-land rice and other food crops in the cleared forest patches, or swiddens, used in cut-and-burn agriculture. Traditionally, the Kantu’ live in longhouses of ten to twenty families. Seven species of birds serve as auguries to determine what crops to plant and when and where to plant them.³² These omen-birds’ songs, locations, and behaviors all instruct individual farmers on their future agricultural decisions.

Individual farmers differ in their orthodoxy to the auguries; “stronger” omens were more likely to be followed than “weaker” ones. The complexity of the interpretations is less important here than to recognize that the omen-bird auguries add an element of randomness into what each farmer does with his swidden planting. Why might such randomness be important? The region is influenced by the El Niño climatic cycles, which manifest as floods in some years and strong droughts in others.³³ If all the farmers planted what worked best last year (or over the last few years), everyone would go down together with crop failures in the periodic bad year.

In this example, using the bird-omen auguries is not predicting anything; instead it is adding a random “bet-hedging” strategy to the local agricultural cropping system. Significantly, planting using bird-omens is not the most productive agricultural strategy in a given year, but it has significant implications for the long-term sustainability of the farming practice. Similar use of auguries to promote a random component and diversity in survival strategies include such diverse cultures as the Naskapi Indians of Labrador³⁴ and swidden agriculturalists on the Philippine Island of Luzon.³⁵

Other auguries are the products of complex chains of interactions that are reliable in their predictions. The arrival of the wandering tattler, the spawning of the Palolo worm, and the best time to plant yams in the Torres Islands all are driven by natural seasonal cycles. The mena of the wandering tattler (and its power as an augury) certainly is mysterious. Simultaneously, it is the product of keen observation and the consequence of several interrelated underlying causes.

Phenology has deep roots in several cultures, and there are ancient traditions of compiling dates of significant natural events. For example, dates of cherry blooming (and cherry blossom festivals) in China and Japan have been recorded for well over a millennium. Modern phenology as a scientific discipline originated with English naturalist-gardeners in the eighteenth century. From his estate Stratton Strawless in Norfolk, Robert Marsham published his record of phenological events (thrush sings, snowdrops flower, swallows appear, wood anemone flower, etc.) for each year from 1736 to 1787.36 Gilbert White from Selbourne, Hampshire, and William Markwick from Battle, Sussex, observed similar seasonal events for over four hundred plant and animal species between 1768 and 1793. These data, reported as the earliest and latest dates for events, appeared in an augmented edition of White’s Natural History and Antiquities of Selborne.³⁷ Natural History³⁸ has been continuously in print since its initial publication in 1789 and may be the fourth-most printed book in the English language.³⁹

Plant phenology is largely regulated by light and temperature. The potential complexity of the environmental control of plant phenology can be remarkable. For example, to germinate seeds of the flowering dogwood (Cornus florida), collect the seeds and then place them in a warm moist environment for sixty days. If rushed for time, put them in sulfuric acid for three or four hours or scratch the seed coat with a file to simulate the conditions of being digested by a bird, the normal way these seeds are dispersed in nature. Then, put them in a cool place—a refrigerator will work—for sixty to 120 days. Finally, cover the seeds with about a centimeter of topsoil, water them, and hope for the best.40 The process is a bit reminiscent of the witch’s brew in Shakespeare’s King Lear, not quite as complex as Macbeth’s “fillet of a fenny snake, in the caldron boil and bake; eye of newt, and toe of frog, wool of bat, and tongue of dog,” but complex, nonetheless.

Different species of plants or varieties of the same species in different locations typically have such complicated formulae to unlock and time the key phases of the life of the plant. In wild plants, the selection pressure pushes evolution to “tune” the plant’s biochemistry to match the environment correctly. This produces local adaptations. Horticulturalists, agronomists, and foresters intensively research the phenological responses of the species so that they can plant varieties to match regions.

The phenological responses of plants often depend on external environmental signals to set the timing of a plant’s growth and development patterns. Moving species from one location to another has produced myriad examples of potentially useful plants failing to prosper when their phenological life history was mistimed to the environment of a new location. Climatic change can produce an analogous mismatch between plant timing and environmental timing. Indeed, climate change has the potential to disrupt ecological processes at several different levels.

In the dogwood seed example, the seeds needed to be warmed for a period of time. Indeed, many plant phenological events need exposure to some cumulative amount of warm conditions, sometimes calculated by number of hours above a base temperature or the summation of temperatures above a reference temperature for each day (called growing degree-days). Also like the dogwood, other plants need to be exposed to a summation of hours or degree-days below a certain temperature (chilling degree-days) before their seeds will germinate or flowers will bloom.

Plants also have the ability to register biochemically the changes in quality, quantity, and duration of light, which provides information on changes in the local environment and in the seasons. For detecting changes in light, plants have evolved a series of highly specialized chemical receptors. These chemicals include the red and far-red light-absorbing phytochromes and the blue/ultraviolet light-absorbing cryptochromes and phototropins. These biochemical molecules “sense” light, but the incorporation of this information into the overall biochemistry and timing of the plant is complex.41 Exposure to progressively longer days induces many species to bloom in the spring. Other plant species are the opposite case. They bloom on shortening days in the fall. Different species use these environmental sensors in one way for one process (flowering on lengthening days in the spring) and in another way for a different process (preparing to drop leaves induced by shortening days in the fall). Manipulating temperatures and day lengths allow horticulturalists to produce blooming orchids, lilies, and other plants year round or to induce tropical poinsettia plants to flower during the holiday season.

Robert Marsham’s phenological observations from his estate in Norfolk, England, the first such records published in English,42 began in 1736 and were continued by five generations of his relatives on the estate until 1947.⁴³ Another significant long record, but of a different sort, was the fifty-year one collected by Charles Keeling, who began measuring the levels of carbon dioxide in the atmosphere atop the volcano Mauna Loa in Hawaii in 1958.⁴⁴ Keeling’s data showed increasing levels of carbon dioxide in the atmosphere. These changes were associated with the burning of fossil fuels and the associated atmospheric release of carbon dioxide. Increases in carbon dioxide and other “greenhouse gases” in the atmosphere strongly imply an increase in global temperature. It is ironic that the Marsham family’s two-hundred-plus-year record of the coming of spring at Stratton Strawless ended before the record of atmospheric carbon dioxide at Mauna Loa began. While the Marshams’ record may have ended, the interest in phenology by early naturalists inspired others to make similar observations. These observations have implications for the magnitude of effects that might come from human-induced climate change.⁴⁵ Indeed, they seem to be signaling climate change in the form of a warming over the over the past several decades.

A phenological network across Europe (twenty-one European countries) has produced a data set of over 125,000 observations of 541 plant species and nineteen animal species. Recent analysis (for the interval of 1971 to 2000) has shown that spring is coming earlier to Europe, about 2.3 days earlier each decade.⁴⁶ Seventy-eight percent of all leafing, flowering, and fruiting records have advanced to earlier times in the season. The primary driving factor appears to be temperature. Indeed, in Europe the pattern of change for temperature measurements indicative of spring have advanced 2.2 days each decade—a strong agreement with an advance of spring seen in phenological observations that we have just discussed.⁴⁷ These temperature measurements all across the Northern Hemisphere indicate that its average “coming of spring” has advanced about 1.3 days each decade.⁴⁸ Other similar temperature findings are an increase in growing-season length, averaging seven days longer since the 1960s⁴⁹ and 1.3 days per decade advance in the last spring freeze in the United States.⁵⁰ There is evidence from British plant phenology (based on 385 plant species) that the rate of spring becoming earlier is accelerating.⁵¹

A different measurement from satellites determines the change in the greenness of the planet. Using daily records of surface conditions obtained from weather satellites, the “greening up” of the vegetation over the Northern Hemisphere became earlier over the decade of 1981 to 1991.52 The greening of spring came earlier over this decade, in total about eight days earlier, and in patterns consistent with computer models of the climate changes expected from greenhouse gas planetary warming.⁵³ Of course, global warming is an expected consequence of doubling the atmosphere’s greenhouse gas content. This was initially predicted in calculations on the physics of the atmosphere made over one hundred years ago.⁵⁴ The magnitude of these estimates (around a 2.5°C increase in average global temperature with a doubling of the amount of carbon dioxide in the atmosphere) has been surprisingly consistent ever since—even with a progression of increasingly sophisticated climate-system models, as scientists have progressed from hand calculations to modern high-speed computers.⁵⁵ This will be the topic for the following chapter.

Three different ways of looking at the Earth’s climate—through collating elaborate phenological data, through processing temperature data, and through inspection of satellite-based observations—all point to an earlier spring in the recent decades. Presumably, increased temperatures drive this change. The ecological responses are seen both at the level of individual species (in the phenological record) and at the level of the responses of the entire ecosystems over a large area (in the satellite data). Given that three different perspectives all point to similar change, it is both wise and prudent to understand the cause of such patterns well.

One of the whirlwind questions quoted at the head of this chapter asked if Job knew when certain animals give birth. The length of life, number of offspring, and the number of times organisms reproduce under different conditions can vary significantly among species as well as within different varieties of the same species.⁵⁶ To survive, it is essential that the life stages of different plants and animals are coordinated with their environment—the genes of individuals prone to have young during times of resource shortage are soon selected out of a population.⁵⁷ This evolutionary selection produces the timing of the births of deer and mountain goats mentioned in the whirlwind question.

How do plants and animals maintain their biological timing? They have “clocks” that can carry timing. These clocks can also be reset or adjusted by external factors in the environment. Many invertebrates have annual spawnings that are synchronized by lunar cycles.58 The striking regularity of the Palolo worm’s biological cycle is something of an extreme example. The Palolo worm’s clock is precise to the day within the year for its spawning behavior, even if clouds hide the moon. The animal and its relatives carry an internal clock that tabulates lunar time.⁵⁹ Most animals do not keep a lunar clock,⁶⁰ but bacteria, fungi, algae, plants, and animals display an internal daily periodicity close to a day, the circadian rhythm.⁶¹ The details of these vary across organisms, but they essentially work by having internal biochemical “oscillators” that keep track of the time of day. One or more of these chemical oscillators, called “pacemakers,” can set their timing by daily variations in the environment, typically the daily cycle of light and dark. These pacemakers then interact with the other oscillators to produce a daily clock.

There is also another internal cycle of about a year, the circannual rhythm, which is found in a wide variety of animals and plants.⁶² In mammals, there are two designs for the biochemical mechanisms that provide the individual with an accounting of the passing of years. Some mammals have what can be thought of as a “timer” that is reset by the seasonal change. Once reset, it has a long interval before it can be reset again. When these interval timers are between being periodically reset by environmental conditions, they provide an internal calendar to the animal. If the animals are placed in constant conditions, then the “timer”-type species run through a series of states: nonreproductive, physiologically able to reproduce, shedding fur, growing new fur, etc. When the timer for these events runs out after six months or so, the individual ceases to change until the timer is reset. Other species have an internal timer that operates more like a clock. These clocks can be reset to the time of year, but when the individuals are placed in constant conditions for long periods of time, their clocks and patterns keep the schedule for years. Like the circadian rhythms, the two types of calendars, timers and clocks, are products of biochemical networks and their internal interactions. It is interesting that there is great variability in how species maintain timing to match the changes in the seasons. Both the clock and the timer circannual systems have evolved independently many times in different species.⁶³ Timers and clocks seem to be the two of many possible ways to anticipate change in the season.

Migratory birds perform remarkable feats using their clocks in conjunction with a surprising capability to travel over large distances. They provide an example of a particularly sophisticated set of internal capabilities.

The phenomenon of bird migration represents a notable example of synchronizing a species’ biological cycles and the periodicities in the environment. The whirlwind question asks by what wisdom a bird flies south (Job 39:26). This issue is alluded to in other parts of the Bible as well. For example in Jeremiah (8:7), “Even the stork in the heavens knows its times: and the turtle dove, swallow and crane observe the time of their coming; but my people do not know the ordinances of the Lord.”

Migration in birds reveals one of the most complex integrations of biological and environmental information to be seen in any organism. Probably among the most remarkable of these avian feats, the wandering tattler sends itself on one of the most arduous migrations of any animal. Departing Siberia and Alaska after the breeding season, it crosses the equator and migrates down the east side of the Pacific, then crosses the great ocean to return home to its nesting grounds by flying up the west side of the Pacific. Not every creature follows migration pathways as challenging as those of the tattler. In birds and other animals with simpler patterns of migration, nomadic movements allow the animals to utilize areas that sometimes would be unusable or even hostile to survival. In either case, the animals must be able to return home.

The classification of animals as migratory or nonmigratory is really a simplification of a range of behaviors and adaptations. Some species do not migrate at all but reside in a given region for all of their lives. Other species appear to be quite opportunistic and erratic in their migrations. Still others are highly programmed and perform improbable feats, like flying across vast expanses of open ocean water or returning precisely to the location where they were born from wintering grounds thousands of miles away. Movement over great distances involves risks. Large-scale migration costs energy and also produces physiological stress. Thus, one would expect migratory behavior to evolve in cases in which the benefits minus the costs of being a migrant are greater than the benefits minus the costs from remaining in place.64

Probably the most straightforward form of migration is the irruptive movements seen in species that are periodically stressed by shortage of food or environmental stresses. Goshawks (Accipiter gentilis) and snowy owls (Nyctea scandiaca) feed on small mammals and birds in the far northern boreal forest and tundra. When there are negative shortages in prey, these striking predators invade regions in North America and Eurasia that are thousands of kilometers further south, often to the great excitement of naturalist birdwatchers. Similarly, seed failures in the cone-bearing trees that make up the dark, coniferous boreal forest spill flocks of evening grosbeaks (Coccothraustes vespertinus) and red crossbills (Loxia curvirostra) south to search for food and to decorate the bird feeders of suburban homes.

The opposite extreme is found in obligate migrants—species that breed in one region during a favorable period and then migrate to faraway wintering grounds when conditions become unfavorable. Obligate migrants are adapted to take advantage of regions with temporary high productivity where there is a pronounced and predictable seasonal variation in environmental conditions. We have already spoken of the wandering tattler. Another obligate migrant is the tiny blackpoll warbler (Dendroica striata).65 These birds breed across the boreal forest of North America to as far west as Alaska. From as much as 2,400 kilometers away for the birds on the Alaskan breeding grounds, black-poll warblers gather in staging areas in New England, perhaps to as far south as Virginia. Fueling up on insects and storing fat, they form small flocks and make an eighty- to ninety-hour, open-ocean flight of 3,500 kilometers across the open Atlantic Ocean to their wintering grounds in South America. This is a truly amazing feat, and it is accomplished by a tiny warbler that normally cannot land at sea. One of the reasons we know that they are out there is that they occasionally do land on ships in the open ocean.⁶⁶

Between the species of either irruptive or obligate migrants are the partial migrants—species composed of some individuals that migrate and others that do not. In some cases, these partial migrant populations differ genetically with respect to traits that involve migration. In other instances, partial migrants have some segments of the populations (such as younger birds or behaviorally subordinate individuals) that are migratory while others are not. In this latter case, an individual can be migratory at one time in its life and nonmigratory at another.⁶⁷

Irruptive, partial, or obligate migrants all need to be able to return “home” to the breeding grounds once conditions have become more favorable there. This is an intrinsically difficult challenge. As well as a sense of location and an ability to navigate to a particular location, the animals need to know when to return. Most people even when armed with maps and compasses would be challenged to get themselves home over several thousand miles of ocean. It is hard to comprehend how small animals with little brains can accomplish such feats. Their toolkit includes clocks, compasses, maps, and evolutionary programming:

Birds, like the other organisms we discussed in the section above, have two clocks built into their physiology. One of these clocks, the circannual rhythm, is more or less like an annual calendar. The other, the circadian rhythm, is more of a daily clock. Much as the Palolo worm and the other examples in the section above, the daily cycle appears to be reset by timing cues from the environment such as the light/dark cycle of the day or daily temperature fluctuations.⁶⁹ The circannual calendar involves the regular progression of internal physiological cycles that are associated with breeding, molting, seasonal changes in plumage, and gains and losses of weight. This circannual cycle is maintained even when caged birds are placed in constant conditions with twelve-hour days and twelve-hour nights. Programmed into the cycles of obligate migrants is a condition called Zugenruhe, a German term for restlessness. In Zugenruhe, birds become more active at night than day. This is the condition associated with readiness for migration in obligate migrants.

If you were boxed in a closed crate and then stuck into a windowless van and driven around the countryside, you likely could not immediately point the correct direction home when discharged in a remote and unfamiliar forest clearing. Pigeons can.70 The sport of homing pigeons is based on returns from just such distant release points under just such conditions. When released, homing pigeons usually fly immediately in the direction of their home roost. There seem to be two aspects in accomplishing this remarkable feat: a “map” to determine position and a “compass” to move in the direction indicated by the map.⁷¹ Birds appear to have four different compasses.

The first such compass is the one most familiar to humans. If one knows the time (which for birds would involve utilizing the circadian clock mentioned above), then the position of the sun in the sky indicates direction. The sun is in the east in the morning and in the west in the afternoon. Homing pigeons apparently can use a “sun compass” to find their way back home. However, many of the obligate migrants fly by night, so they must be equipped with other navigational tools as well.

The second compass is the ability to read stars. At night, caged birds in a state of migratory unrest or Zugenruhe will hop on the side of their cages in the direction that they would move if they were free and making a migratory flight. When these birds are placed in a planetarium, experiments on bird navigation can be conducted under the planetarium’s artificial starry skies, which can be manipulated by changing the projector. In the planetarium with changed skies, birds change their direction of hopping, as if they are star navigating. It appears that birds learn the stars of the night sky in the first year of their lives and are able to use the stars as a second compass.

The surprising third compass that birds (as well as several other animals) appear to have is the ability to sense magnetic fields. The lines of force in the Earth’s magnetic field are vertical over the magnetic poles and become flatter as one moves away from the magnetic poles. A bird uses its sense of magnetic fields and determines the dip angle or verticality of these lines of force and thus is provided a sense of direction.⁷² Migratory birds in Zugenruhe held in the same sorts of experimental cages used in the planetarium experiments can be placed in controllable magnetic fields using Helmholtz coils. When the magnetic field surrounding the birds is altered, so is the direction of hopping movements in the cages.⁷³

Birds have a fourth compass, a sense that humans also have but rarely utilize. This is the ability to sense polarized light. If you look at a lamp through a polarized sheet of plastic (or even polarized sunglasses), a yellowish hourglass figure appears. It rotates when you rotate the plastic sheet. This figure, called “Haidinger’s brush,” points in the direction of the polarization of the light.74 It can also be seen looking at a white area on a LCD flat-panel computer screens. Haidinger’s brush is relatively easy to observe under the correct conditions, but our brains usually edit this phenomenon out of our perception. It is not clear what birds see, but they can detect the pattern of the polarized light that is created by the atmosphere acting as a weak polarizing filter on sunlight. Thus, birds know the position of the sun from patches of sky even when the sun is obscured from view. Similarly, insects can detect polarized light and use this information as a sun compass.⁷⁵

Geese and cranes dependably return to the same stopover points during migration in different years. This indicates a rather precise ability to navigate from year to year. Armed with their multiple compasses, birds have the information to sense direction under a range of conditions: daytime or night, cloudy or clear. An accurate clock and the knowledge to read the stars, tell north from south, detect the dip of the Earth’s magnetic fields, and determine latitude are certainly sufficient information for navigation. However, the calculations are complex, and the clocks and senses would need to be remarkably accurate to allow birds to migrate with the exactitude that some birds are known to have. Without a superaccurate clock but armed with a compass (or multiple backup compasses), one still needs a map to navigate back to home base. We know less about how this aspect of avian migration works.

Much of the work to understand the map used by birds has been done with homing pigeons. That homing pigeons can return to their lofts even when fitted with frosted contact-lenses implies that senses in addition to sight are involved.76 Birds are now known to have small organs in their heads that contain magnetite crystals—this provides a magnetic sense.⁷⁷ Pigeons appear to use the magnetic fields and magnetic anomalies (places where, for example, large iron ore deposits disturb the pattern of the Earth’s magnetic fields) as maps. There is evidence that pigeons and other birds may use a sense of smell for certain odors blowing in winds from different directions to find their way.⁷⁸ It has also been proposed that birds can use the inaudible, extremely low frequency sound called “infrasound” that is generated by the Earth’s surface as a kind of map based on sound reflections.⁷⁹ It seems plausible that long-distance migrants could use their sense of direction and clocks to travel in appropriate directions at appropriate times and to then use magnetic, chemical, or infrasound clues to find their homes. The direction taken by birds on their first migration appears to be inherited genetically.⁸⁰

The migratory phenomena can develop (or be lost) from a population in a relatively short period of time, even in obligate migrants.⁸¹ Ten thousand years ago, the breeding areas that blackpoll warblers now target for their spring return were covered by continental glaciers or equally inhospitable polar deserts. Thus, the complicated behaviors of long-distance migration must have developed in this obligate migrant during this period of time. Ten thousand years is relatively short in the scope of evolutionary changes, but development and loss of migratory behavior has occurred in short enough time periods as to be observed by human observers—in time spans measured in decades rather than in millennia.

The nonmigratory house finches (Carpodacus cassinii) introduced to Long Island, New York, in the 1940s have now spread across the upper half of the eastern United States. The species is a common bird-feeder visitor in suburbs of the east and has become a partial migrant. Rufous hummingbirds (Selasphorus rufus) from the Pacific Northwest of the United States and Canada that normally migrate to Mexico for the winter now have learned to migrate by the hundreds to backyard hummingbird feeders in the southern states of the Gulf Coast. Other migratory species when introduced to new situations have become nonmigratory in equally short periods of time.82

In a time when some see religious faith at odds with science, it is worthwhile to remember that the scholarly observation and interpretation of the natural world were significant positive attributes in biblical sages.⁸³ For example, King Solomon, the epitome of a royal sage, was characterized as a man of great wisdom and insight into the workings of the Earth:

For it is he who gave me unerring knowledge of what exists, to know the structure of the world and the activity of the elements; the beginning and end and middle of times, the alternations of the solstices and the changes of the seasons, the cycles of the year and the constellations of the stars, the natures of animals and the tempers of wild animals, the powers of spirits and the thoughts of human beings, the varieties of plants and the virtues of roots; I learned both what is secret and what is manifest, for wisdom, the fashioner of all things, taught me.

(Wisdom of Solomon 17:17–22)⁸⁴