To understand the concept and implications of extinction using the example of the Passenger Pigeon, once an extremely abundant species that was completely eliminated by humans. To understand that technologies that were seemingly unrelated to the loss of the bird were actually central to its extinction.
This lesson was developed by two scientists, Drs. Penny Firth of the U.S. National Science Foundation, and David Blockstein of the National Council for Science and the Environment, as part of a set of interdisciplinary Science NetLinks lessons aimed at improved understanding of environmental phenomena and events. Some of the lessons integrate topics that cross biological, ecological, and physical concepts. Others involve elements of economics, history, anthropology, and art. Each lesson is framed by plain-language background information for the teacher, and includes a selection of instructional tips and activities in the boxes.
The history and ecology of North America are intertwined in a variety of ways. Students should be generally familiar with how the continent was settled, and how the telegraph and the railroads made communication and movement easier. In the case of the Passenger Pigeon, these developments brought slaughter, habitat destruction, disturbance of nesting, and ultimately extinction.
Students, having never seen a Passenger Pigeon, may have trouble appreciating that this is a bird that they will never get to see alive. There are several familiar pigeons still around, including the Mourning Dove, the Rock Dove or "city pigeon," and the domesticated Carrier Pigeon or "homing pigeon." But the Passenger Pigeon, once one of the most abundant birds in the world, has been lost from the planet forever. Students who are familiar with the film Jurassic Park may ask if the Passenger Pigeon can be brought back from DNA that might be recovered from museum specimens. The answer, at least for the present, is no.
It will be important for students to try to picture the North American forests as they were before they were cleared by European settlers. These forests were immense, far beyond anything that still exists in the temperate zone today. They periodically produced superabundant crops of mast. The word mast is from Old English mæst, meaning tree fruits such as nuts and acorns. Enormous Passenger Pigeon flocks located and fed on these seasonal mast crops. Understanding a little about mast will help students with this lesson.
Although mature trees produce some fruit every year, approximately every three or four years all of the oaks, beeches, and similar hardwoods in a region will produce a vast fruit crop. Such years are called "mast years" and the mast provides important food for forest animals such as deer, mice, turkeys, and—until a century ago—Passenger Pigeons. Predicting when and where a mast year will occur is very difficult, and scientists are just beginning to understand some of the environmental factors that seem to be involved (e.g. winter temperatures, El Niño). Masting is an important way that trees can satiate most seed eaters. By producing more seeds than will be eaten, the trees ensure that some seedlings will survive. You can ask students to look for oaks and beeches along the streets and in the parks near their homes. If they bring in fruits to show the class, remind them that Native Americans ate both acorns and beechnuts.
The scientific name of the Passenger Pigeon is Ectopistes migratorius. Ecto is from the Latin for "outside" and piste is from Italian for "trail." Ectopistes might be translated as "wanderer" or one who goes off the trail. Migratorius is from the Latin migrare, meaning "to change location periodically." Thus, the bird is very descriptively named the migratory wanderer. Incidentally, the common name was originally in French, "Pigeón de passage" or "pigeon of passage" because of the astounding size of the migratory flocks passing overhead.
This lesson will help the class consider the human forces that drove the extinction, including both the collective mentality regarding conservation and the new technologies that made extinction a possibility. The lesson will also show how the biology of this bird locked it into a death spiral once its population had declined below a critical threshold. Finally, the lesson will suggest some implications of the loss of an abundant species for the ecosystems of which it was a part and how events that occurred a century or more ago can impact our modern world.
Contact Dr. Firth at firstname.lastname@example.org.
What was happening in the United States in the last century of the Passenger Pigeon? We have provided a simple timeline of the 19th century in Passenger Pigeon Timeline. As a class activity, you may want to draw a larger version of this timeline on a large sheet of paper and hang it where students can see it. Using this paper, help your class mark it up with other historical events of the century. We have provided some possibilities on the Events to Consider for Passenger Pigeon Timeline. Students should feel free, however, to consult history books or do Web searches on topics of interest to them. Some examples might include African American history, Native American history, military history of the Civil War and Reconstruction, history of science and technology, art history, social history, music history, women's history, political history, history of cooking and domestic arts, and transportation history.
Once students have completed their timelines, discuss with them how the world of the 19th century differed from our present world. Why do they think it might be good to study an animal that no longer exists? Are there lessons that can be learned from this extinction that might have application today?
THE STORY OF THE PASSENGER PIGEON
In this section, students will be guided through the story of the Passenger Pigeon, including what the bird was like, how it migrated, how it raised its young, its strategies for survival, and finally the factors that led to its extinction. Throughout this section, you will be provided with substantial background information that you can use with your students, as well as some guiding questions and activities that they can do to help them understand how this bird became extinct.
When North America was being settled, the vast forests of the East and Upper Midwest supported immense numbers of a bird that no longer exists: the Passenger Pigeon. For centuries, they were used for food and other products by Native Americans. When European settlers arrived, they took advantage of the pigeons as well. In migration, their flocks—a mile wide and up to 300 miles long—darkened the sky from morning until evening as hundreds of millions of birds moved across the landscape. When these pigeons landed in massive numbers to roost, they broke down trees, covered the ground with a thick layer of droppings, and stripped the berries, acorns, and other food items from large areas. The Passenger Pigeon was probably the most numerous land bird on the continent.
It was when nesting that they were most vulnerable to predators, including humans. Adults and young (called squabs, a Scandinavian word meaning "fat flesh") were shot, netted, and knocked from their nests with poles. Trees containing hundreds of nests were cut down or set afire so that people could get the young birds, which were prized for their tasty meat. There was enormous waste as birds were killed for feathers, hog food, oil, and sport (trap-shooting). By today's standards, the extent of the slaughter was cruel and senseless. But when one of every three or four land birds in all of North America was a Passenger Pigeon, it was impossible to imagine that they could go extinct. The Passenger Pigeon needed large flocks to survive, from feeding to nesting in gigantic colonies. Without vast numbers, it slipped below a sustainable threshold very rapidly.
The Passenger Pigeon is now extinct. Destruction of nesting colonies prevented recruitment of young into the population and doomed the species. Recruitment in a biological sense means to successfully rear young to adulthood. Other factors, such as hunting and the clearing of forests to make way for agriculture, also contributed. The decline was well under way by the 1850s but accelerated out of control in the 1860s and 1870s—over a 30-year period there were no uninterrupted mass nestings, which were necessary to sustain the population. By 1900, they were all but gone. Rewards of up to $1,000 for information leading to finding a nesting pair or colony were never claimed.
WHO WAS THE PASSENGER PIGEON?
The Passenger Pigeon looked similar to the familiar Mourning Dove, but was about six inches longer, and colored differently. It had a long pointed tail and "brilliant fiery orange" eyes. The Chipper Woods Bird Observatory provides photographs of a stuffed specimen. Multiple paintings of the bird are available on the Passenger Pigeon Society website. One that we found most useful is a 1906 painting by Louis A. Fuertes listed as "Fuertes of the Passenger Pigeon and Dove." In this painting, the relative size of the Passenger Pigeon compared with the Mourning Dove is obvious.
Passenger Pigeons were found in deciduous forests and bred primarily in the Northeast and Upper Midwest. The clearing of forests and disturbance of nesting colonies exterminated them first in the East. They probably declined beyond the point of recovery by the late 1880s in the Midwest.
Vast Passenger Pigeon nesting colonies were established where significant mast remained from the previous winter. These colonies, called "pigeon cities," were up to 850 square miles—almost twice the size of the city of Los Angeles! In 1871, the largest nesting ever described covered most of the southern two-thirds of Wisconsin, with other nestings in adjacent Minnesota. Within the nesting area, nearly every tree held nests, and sometimes scores of nests were built in a single tree. (A score is a group of 20.) In fact, when roosting or nesting, birds packed extremely densely, to the extent that observers often reported pigeons piled atop one another. In roosts, the number of birds that tried to land on a branch was often so great that even thick branches broke beneath their combined weight.
How Big Were the Colonies?
Migrating flocks of Passenger Pigeons were a stunning sight. The extravagant numbers of birds flying over for hours at a time inspired many to record vivid word images such as countless numbers, blocking out the sun, flocks with neither beginning or ending, length or breadth, processions as far as the eye could reach, flocks passing like a living torrent.
Several people attempted to estimate the numbers of birds in some of these superflocks by estimating the breadth of the column, the rate of speed of the birds, and how dense the birds appeared to be. Can you imagine a flock of a billion birds? How about one three times that size? These were the estimates of some experienced observers.
The speed, maneuverability, and flying ability of the Passenger Pigeon were legendary. Flocks wandered in response to short-term changes in food supply and weather, and their swift flight (over 60 mph) allowed them to cover a lot of territory in a short time. In an interesting behavior, the flocks followed exactly the movements of birds in front, so that if those birds swerved to avoid a predator, the following birds swerved as well, even long after the predator was gone. This meant that the flocks behaved like colossal ribbons in the sky, weaving and swooping along: an awe-inspiring sight for all who saw them.
PASSENGER PIGEON STRATEGIES
Much of Passenger Pigeon ecology and behavior can be considered a response to predators. The immense numbers of individuals that congregated in breeding and migrating flocks effectively satiated predators. There were simply so many pigeons in a flock that not only was each individual effectively shielded by the others, but no predator could make a dent in their numbers. Scientists now believe that once the species' numbers had declined to the point where predator satiation was ineffective, predation at the nest was a major factor that led to extinction.
Now review with your students masting (synchronous seed set over a large area, such as by oaks) that we described in the Context section. Masting also effectively satiates predators: seed predators such as birds and deer. At least it does these days. Ask your students whether they think the large-flock foraging behavior by Passenger Pigeons made masting a less-effective strategy for the trees. Might the evolution of the Passenger Pigeon have been influenced by the masting of the trees? Which do they think came first?
Each pair of Passenger Pigeons laid a single white, slightly glossy egg in their nest and the parents took turns incubating it for almost two weeks before it hatched. The nestling was fed "crop milk" by both parents for a few days before softened mast was introduced. Bird milk is an extremely rich food, mostly lipids, proteins, vitamins, and minerals. All members of the pigeon family produce crop milk, and it is one reason that pigeons have the fastest growth rate of any nestling birds. Ask your students to name other animals that produce one offspring per mating (e.g. deer, humans). Now ask them to name some animals that produce multiple offspring per mating (e.g. many insects, most birds). How big a parental care investment do the parents of single offspring make versus the parents of multiple offspring?
Passenger Pigeon parents reportedly abandoned the colony en masse when the nestlings were two weeks old, before the tubby youngsters could fly! Fledglings were a mass of fat—sometimes heavier than their parents—and were greatly sought out by humans for food. Once abandoned, fledglings sat in the nest begging for a day or so, and then fluttered to the ground, where they begged from any adult that was in the vicinity. (If this sounds funny to you parents of young adults, I’m not telling it right.) After three or four days, the little lardballs could fly well enough to escape human capture by hand, and within a week all of the fat had been absorbed. Now that's a weight-loss plan!
The hundreds of millions of birds in the nesting colonies spent late summer moving through the northern forests and wetlands searching for berries, acorns, and other food. In autumn, flocks of Passenger Pigeons began their migration to southern wintering areas, seeking food sources and appropriate roosting habitat.
THE TECHNOLOGIES OF EXTINCTION
Every Passenger Pigeon colony that was accessible to humans was exploited. There were no laws restricting the way pigeons were killed, and certainly no limits on how many could be taken. What limited the take for a while was lack of access to markets for the meat, fat, and feathers, as well as inefficient communications that kept hunters from easily finding the roosting and nesting sites. People killed as many birds as they could use locally, but until the great city markets were accessible, the impact on pigeon populations was minimal. The late 19th century saw revolutionary changes in human infrastructure, most notably the greatly expanded railroad system and the telegraph. In addition, the population of the country was exploding, from just over 5 million people in 1800, to 23 million in 1850, to 76 million in 1900. (Incidentally, there are now over 280 million people living in the United States.)
Railroads allowed easy access for market hunters to reach nesting colonies and ship millions of pigeons out for city markets. The telegraph provided a way for scouts who located colonies to inform the professional pigeon trappers. When professional hunters started netting and shooting the pigeons for city markets—where they often sold for as little as fifty cents a dozen—the populations began to noticeably decrease.
|Where Were the Railroads? And When?
Take your students to this Railroad History site where they will see important milestones in English and American railway development. How quickly did railroads expand? What forms of transportation did they replace? How did the telegraph (whose lines usually followed the railroads) change communications?
If railroads had never existed, do you think the passenger pigeon might have survived? What is the difference between commercial market hunting and other kinds of hunting? Since all of the market hunters of passenger pigeons had a stake in the pigeon's continuing survival, why do you think they failed to work together to conserve the species?
Often hundreds of thousands of adults and squabs were shipped from a single nesting. Large numbers of birds were destroyed by locals or otherwise killed but not transported. A million birds could be lost at a single nesting. Yet overhunting did not exterminate the Passenger Pigeon as is commonly believed. Rather, the disturbance of the nesting colonies led the birds to abandon the nestlings prematurely. This, together with slaughter of nestlings as well as adults, largely eliminated replacement of the population. As late as 1878, tens of thousands of birds were killed per day at a mass nesting near Petoskey, Michigan. When the adult birds left and attempted a second nesting, they were located by professional hunters and killed before they had a chance to raise any young. Thus, for nearly thirty years, well over twice the lifetime of the average bird, there were not successful mass nestings.
Deforestation was also a major factor in the decline, because it reduced the opportunities for nesting and roosting colonies. Because nesting colonies formed only where there was sufficient mast, the reduction in the forest meant that in some years, there was no nesting at all. The portable saw mill, introduced in the 1870s, sped the destruction of what had once been a completely forested landscape. By 1880, about 80% of the original forest of New England had been cleared. Deforestation occurred from east to west, following settlement, but the pigeons disappeared before the last deciduous forests were cut. Students can view the Forests—Human Impact video, from the PBS American Field Guide to get an idea about how humans affect the environment.
Because of the loss of forests and the persecution by humans at what had been ideal nesting sites, the Passenger Pigeons were driven to nest farther north and west and under conditions that were less favorable (i.e. less food, colder temperatures). Eventually, the larger part of the great flocks consisted of old birds. Once the population reached a level of thousands, rather than billions, the species was unable to recover. But persecution continued nearly to the end. Scientists believe that by 1892, the majority were no longer breeding in colonies, but rather in isolated pairs. This would make them extraordinarily vulnerable to predation. It is also possible that the smaller flocks might have had difficulty finding food patches (masting forests) large enough to sustain themselves because the species had evolved to depend on "social facilitation" of foraging. That is, the large numbers of birds could cover huge territories when foraging for mast and thus find and exploit patches that might be missed by smaller flocks. By the time the Passenger Pigeon population was reduced to individual pairs, foraging was likely not a problem.
In any case, the point is that the Passenger Pigeon had evolved certain strategies for success as a species, namely predator satiation and social facilitation of foraging. Once its numbers dropped below the level necessary to achieve these evolved strategies, the population was unable to maintain itself. Ironically, it was the massed, colonial way of life—necessary for the survival of the species before humans—that made human slaughter, disruption of nesting, and ultimately extinction, possible.
To gauge student understanding about the various causes of the extinction of the Passenger Pigeon, ask questions like these:
- What two technologies contributed significantly to the decline of Passenger Pigeon populations?
- How is it that these technologies helped to bring about the extinction of these birds?
- How did population growth in the United States impact the Passenger Pigeon?
- What effect did deforestation have on the birds' opportunities for nesting and roosting. What about food?
- How did the Passenger Pigeon's own survival strategies contribute to its extinction?
The last recorded wild Passenger Pigeon was shot by a 14-year-old boy of Sargents in Pike County, Ohio on March 24th, 1900. The boy, Press Clay Southworth, died at the age of 94 in 1979. In 1970, he recounted the details of that day:
- While feeding the family cows, Press observed a strange bird eating grains of corn in the barnyard. He was very familiar with local birds but did not recognize this one. Young Press asked his mother for permission to take the shotgun and shoot the bird, which he most certainly did in a single shot. His parents quickly identified the bird as a Passenger Pigeon, having seen them in great numbers in their youth. They told him to take the bird to a local lady who was known to do taxidermy. Mrs. Barnes mounted the Pigeon and used buttons for its eyes, hence the birds' nickname "Buttons." Many years later, Mrs. Barnes offered the bird to the state museum in Ohio, and apparently it was not until then that ornithologists determined it to be the last authentic record of a wild Passenger Pigeon.
A group of Passenger Pigeons lingered in captivity in the Cincinnati Zoo for the first years of the 20th century. The last remaining bird died on September 1, 1914. Her name was Martha (named after Martha Washington), and she was the last individual of one of the most abundant bird species on the entire planet!
Have your class do a group reading of this passage by Aldo Leopold, from A Monument to the Pigeon, 1947. Assign from one to three students per phrase.
Men still live who, in their youth remember pigeons;
trees still live that, in their youth, were shaken by a living wind.
But a few decades hence only the oldest oaks will remember,
and at long last only the hills will know.
We grieve because no living man will ever see again
the onrush of victorious birds,
sweeping a path for spring across the March skies,
chasing the defeated winter from all of the woods and prairies.
There will always be pigeons in books and in museums
but they are dead to all hardships and to all delights.
They cannot dive out of a cloud,
nor clap their wings in thunderous applause.
They know no urge of seasons;
they feel no kiss of sun,
no lash of wind and weather,
they live forever by not living at all.
CENTURY-OLD LEGACIES CAN IMPACT THE MODERN WORLD
The Passenger Pigeon moved a lot of plant nutrients across the landscape. The birds would regularly fly 60 to 80 miles in the morning to forests rich with mast, and return to the roost site in the evening. Imagine these ecological engines of movement, millions of them, flying dozens of miles each day and roosting in massive flocks. As they ate and defecated, prodigious quantities of dung accumulated under the roosts. Dung, as you probably know, makes very good fertilizer. We will never know how the loss of this ecological service affected soil fertility and forest ecosystems in Eastern and Midwestern North America.
Ask your class where fertilizer comes from, and how it might move across the landscape today. Mixed commercial fertilizer was first sold in 1849. According to the History of American Agriculture, from the Agriculture in the Classroom project, it quickly became popular, so that during the 1890s, the average annual consumption of commercial fertilizer was 1.8 million tons. By the 1920s, 6.8 million tons were used annually, and by the 1960s, 32.4 million tons were applied annually.
Are there any migratory animals that move nitrogen, phosphorus, potassium, and other elements around on a large scale? (Hint: Think of land animals such as the grazing herds on the Serengeti Plain in Africa, as well as aquatic animals such as salmon.)
Could an event that happened one hundred years ago cause health risks in our woodlands and suburban backyards today? Could the Passenger Pigeon’s extinction have contributed to current outbreaks of Lyme disease?
Ecologists Richard Ostfeld and his colleague Clive Jones, based at the Institute of Ecosystem Studies, in Milbrook, NY, discovered the relationship between the masting patterns of oaks and the occurrence of Lyme disease. In The Acorn Connection, Dr. Jones describes interrelations among Lyme disease, Gypsy Moths, forest masting, deer, and mice. These scientists noticed that Lyme disease risk increases two years after a bumper crop of acorns (i.e. a mast year). The story they discovered is complex, but fascinating: Deer move into the acorn-rich area, Ixodes ticks attach and feed, then drop off and lay eggs the following summer. The woods are now thronged with larval ticks. White-footed mice are also fattening on the acorns, and their local population skyrockets. Now you have woods full of larval ticks and mice. The ticks attach to the mice (most of which carry the Lyme disease pathogen) and get a tasty mouse-blood meal. A year later, the ticks have matured. The area that, two years ago, had an abundance of acorns now has countless disease-carrying ticks. Unfortunately, these ticks attach to humans and pass on Lyme disease to the unwitting blood donor. The Centers for Disease Control Lyme Disease homepage shows images of the life stages of the deer tick as well as the bacterium that causes the disease: Borellia burgdorferi.
In the days of the Passenger Pigeon, enormous flocks of southbound birds searching the landscape for mast fed on acorns. According to one observer, “In their travels they make vast havock [sic] among the acorns and berries of all sorts, that they waste whole forests in a short time, and leave a famine behind them for most other creatures.” Why is Lyme disease so prevalent now compared with a century ago? We know that deer populations have increased since the beginning of the 20th century due to the loss of large predators and changes in the landscape. Could the absence of Passenger Pigeons, and hence greater availability of mast, also have contributed? We will never know.
Some states approved laws prohibiting disturbance at Passenger Pigeon nesting colonies, but the laws were weakly enforced and were for the most part, too late. The density and abundance of the pigeons were such that few people recognized that there were any risks to the species. Arguments that there was no need for protection generally doomed any proposed legal protection. In any case, the forest clearing, farming, and railroads that came with an expanding population were diametrically opposed to the needs of the Passenger Pigeons: huge deciduous forests.
Watch the PBS American Field Guide video entitled Wildlife - The Age of Extermination. The focus is on the state of Alabama, but the lessons apply everywhere. Discuss with your class what was meant by the phrase manifest destiny. Were there any laws governing market hunters? What famous people called for conservation? Were any of them politicians? Were any of them writers? What were the effects of their efforts?
The one valuable result of the extinction of the Passenger Pigeon was that it aroused public interest in the need for strong conservation laws. Because these laws were put into effect, we may have saved other species of our migratory birds and wildlife. The extinction of the once limitless flocks of pigeons, along with the near extermination of the American bison, introduced Americans to the concept of human-induced extinction, and helped the beginnings of the conservation movement.
Students should now be familiar with the story of the Passenger Pigeon in the context of the history and ecology of North America. They should understand the concept and implications of extinction and understand that technologies that were seemingly unrelated to the loss of the bird were actually central to its extinction. They should also appreciate that events that occurred a century or more ago can impact our modern world.
In order to bring this lesson to closure, have your class, working in pairs or teams, design and construct a Passenger Pigeon Totem Pole from styrofoam, cardboard, or similar lightweight materials. The vertical sections of the totem pole could represent any of the take-home messages from this lesson. For example, the vast numbers of pigeons that once lived on this continent (feathers, images), the forests that supported the flocks (acorns, branches), the nesting colonies (abandoned bird nests, or student-constructed nests), the animals that shared the Passenger Pigeon food web (raptors, foxes), the technologies that were central to its extinction (wire, toy train tracks), the market hunters that exploited the nesting colonies (Monopoly money, nets), and the impacts of extinction (toy bugs, fertilizer, conservation advocacy).
Ask students to be as creative as possible in representing what they learned from this lesson. Each team should be given about 5-6 minutes to explain to the class what they have put on the totem pole and how it relates to the messages of this lesson.
Then, invite student reporters from the school newspaper to come photograph the totem pole and its architects, and invite them to write a story with the message from the students: Just because a resource is superabundant, does not mean that it cannot be completely eliminated. Understanding how biology, technology, ecology, history, and economics are interrelated is very important.
The PBS American Field Guide video Forests – Human Impact presents different opinions on present forest management, as well as depictions of Native American use of forests, effects of settlement and market exploitation, and regrowth in recent decades. One of the points made in the video is that many hardwood forests have been replaced by pine plantations. If the Passenger Pigeon had survived, how might this have affected it?
Passenger pigeons were important food resources for animals such as foxes, lynx, marten, and mink, and for several raptors, such as falcons, hawks, and owls. How would the loss of this food source have affected the predator populations? Might smaller predator populations have caused changes in the populations of other prey species? If these other prey species were herbivores, how might this have affected the populations of plants that they fed on?
Many people see the Rock Dove, a relative of the Passenger Pigeon, every day in American cities. Some would say there are far too many of them, especially when looking for a clean park bench to sit on. Can you imagine the Rock Dove becoming extinct? Why or why not?
Are there other species that seem very abundant, but may be close to slipping below the threshold of survival? Colonial water birds or seabirds such as these Snow Geese, for example? Colonial habits increase the vulnerability of species to exploitation and extinction.