The Geography of Bird Migration

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This article was downloaded by: [University of Missouri Columbia]On: 17 March 2013, At: 20:34Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UKJournal of GeographyPublication details, including instructions for authors and subscription information: Geography of Bird MigrationPhilip R. PrydeVersion of record first published: 16 Aug 2007.To cite this article: Philip R. Pryde (2002): The Geography of Bird Migration, Journal of Geography, 101:5, 207-221To link to this article: SCROLL DOWN FOR ARTICLEFull terms and conditions of use: article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.The Geography of Bird Migration Philip R. Pryde ABSTRACT The following material has been designed as a curriculum module to famil- iarize students with the geographic con- cepts associated with the migration of North American birds. These concepts include breeding territories, orientation, weather factors, mapping, and flyways. This module would be most suitable for grades 4 to 8. The subject matter is inher- ently interdisciplinary in nature, encom- passing concepts from geography, the nat- ural sciences, and environmental studies, and should help meet "teaching across the curriculum" requirements. It can also be adapted to extra-curricular offerings, such as special after-school classes or courses taught by organizations such as the Audubon Society. Teachers may modify the material to match the classroom time they have available. Key words: migration, breeding habitat, f l y - ways, orientation, wintering habitat Pkilip R. Pryde is. a professor in the Department of Geography at San Diego State University. His teaching and research inter- ests include geographical aspects of environ- mental policy, with an emphasis on preserved natural areas. He is also a past president of the San Diego Audubon Society, for which he leads field trips and teaches courses on the field identification of North American birds. INTRODUCTION nating subjects for adults and children alike. The migration of birds has intrigued people for thousands of years, having been discussed by Aristotle, among many others. North American interest in bird migration dates back at least to the observations of the artist Mark Catesby (1682-1749), and the writings of William Bartram (1739-1823) (Cruikshank 1957; Field 2000). In 1918 Congress passed the Migratory Bird Treaty Act, which gave the first legal protection to migratory birds. Many fascinating works exist on the topic of where and how birds migrate (Able 1999, ch. 2; Berger 1961; DeGraaf and Rappole 1995; Elphick 1995; Hagan and Johnston 1992; Mead 1983; Rappole 1983,1995). In recent years attention has been increasingly directed to the apparent reductions in numbers of many migratory bird species and to losses of their habitats (Martin and Finch 1995; Terborgh 1989). For a book on bird migration written in a more popular vein, try Weidensaul (1999). Here, the subject of bird migration is presented as a curriculum module designed to acquaint students with the geographic concepts inherent in patterns of bird migration in the Western Hemisphere. It is designed for use by students in grades 4 to 8. Components of the module include: Why birds migrate, The mechanics of migration, Other aspects of migration, Migration and habitat, and a classroom exercise and reading assignment. This curriculum module address- es National Geography Standards 1, 8, 14, and 26. reasons why birds migrate, how they do it, and what some of the most impor- tant geographic aspects of migration are. The emphasis is on neotropical migrants (birds that migrate from North America to Central and South America and the Caribbean - see Glossary in Appendix E), though other interesting migrants are discussed as well. Secondary goals are to acquaint students with a variety of bird families, to increase their familiarity with the political subdivi- sions of North and Middle America, and to help develop their atlas and map- ping skills. The material as presented here is designed as a guide for teachers. A one-page reading assignment for students in grades 4-6 is included as Appendix D. The homework exercise (Appendix A) is most suitable for grades 6-8, but can be attempted in grades 4-5 at the teacher's discretion. Teachers may modify the material as presented here to match the time available for presenting this unit. WHY Do BIRDS MIGRATE? excessively cold weather and to reach a more reliable food supply during the winter season. The farther north you live in North America, the shorter the growing season, and the Ionger the coId season with reduced food supply and higher energy requirements. Thus, for most birds, a reliable food base exists in the northern regions only in the summer months. In most cases this means Birds, and their manner of flight and migration, are intrinsically fasci- The primary goals of the module are to familiarize students with the The main reasons that birds migrate southward in winter are to avoid Journal of Geography 101: 207-221 02002 NationaI Council for Geographic Education Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 208 Pryde migrating to a warmer climate during the winter, where food will be more readily available. But if there is adequate food in their wintering region, why then do they fly north in summer? One expla- nation of the northward migration phenomenon is that for some species of birds, nesting in the more northerly forests or sub-arctic may have some distinct advantages. Among these are less competition for nesting sites and food and a more predator-free environment. Some types of carnivores that elsewhere would prey on juvenile birds (such as snakes) are relatively scarce in the far north. Also, summer days are longer in the north, and thus more feeding time is available. The longer days also produce smaller diurnal temperature changes, another advantage for newly-hatched chicks. long-distance migration to breeding grounds. For example, consider birds that nest in boreal conifer forests. At the end of the ice ages, the northern limit of conifers was prob- ably much farther south than it is today. As the glaciers retreated, and climate gradually became warmer, conifers began growing in increasingly higher latitudes. The birds took advantage of this, colonizing the new conifer forests as the trees advanced farther and farther north. With time, what might have been a relatively short migration to suit- able winter habitat became a journey of many hundreds, or even thousands, of miles. At the same time, a tendency towards over-population on traditional breeding grounds may have pushed some members of essentially tropical species towards the less heavily populated new forests to the north. incentive for migration than cold temperatures (Greenberg and Lumpkin 1991). Even small birds such as chickadees will remain in their breeding areas throughout the winter, despite occasional bitterly cold temperatures, because their food supply remains plentiful and accessible. In a similar manner, well-maintained bird feeders will induce some individuals of species that normally migrate to over-winter in a residential neighborhood. Note, though, that this prac- tice might prove harmful to some birds if the person tend- ing the feeder happens to move away in the middle of a particularly harsh winter. Long-term climatic change may also help explain A reduction in food supply is a more important Do all birds migrate? no need to migrate, as food and warmth are available year- round. Even in mid-latitude regions (such as most of the United States), some species (most types of woodpeckers, grouse, and jays, for example) can find adequate suste- nance throughout the year, and do not need to migrate to more tropical realms. But in the northern states and in Canada, most species do migrate. One study found that of 215 species of breeding birds in the state of Michigan, fewer than 20 did not migrate at all (Berger 1961). ber of species, such as snowy owls, ravens, and snow No, not all. Most species of birds in the tropics have In extreme northerly latitudes, only a small num- buntings, are able to adapt to winter-season conditions. There are various mechanisms that allow this to take place. In most cases, over-wintering birds have food preferences that are available year-round, such as seeds for chickadees. Thus, they have a reliable energy supply that enables them to survive the cold winter months. Their feather structure usually has excellent insulation properties, as well. In a few cases, certain species are able to engage in torpor (meaning their heart rate, body temperature, and metabolism markedly slow down) during long, cold winter nights, or even for a few days at a time. Only one species, the poor- will of the American West, has been suggested as engagng in all-winter hibernation (Jaeger 1948). Vertical migration Migration doesnt always have to be latitudinal, that is, occurring in basically a north-south direction. It can also be altitudinal, or vertical. In this latter type of migration, certain birds will move seasonally up and down the slopes of major mountain ranges. During summer, food sources and attractive habitat will be available at the higher eleva- tions; conversely, food is more readily available at the lower elevations in winter. Rosy finches, pine grosbeaks, and some species of chickadees, nuthatches, and jays are exam- ples of North American birds that engage in vertical migra- tion. Some populations of juncos migrate vertically, while other juncos travel hundreds of miles north in spring and south in fall (USFWS 1979, 91). Two anomolies are mountain quail and blue grouse. Mountain quail, apparently in no great hurry, walk down the mountainside in fall. Blue grouse breed at lower mon- tane elevations and winter in high elevation pine forests (Berger 1961, 119). tical feet up a mountainside is the equivalent of travelling about 300 miles northward. In both cases, the cooler cli- mate restricts vegetation. This is why the treeless tops of high mountains are called alpine tundra. area (about 5,500 feet elevation) to a meadow at 9,500 feet in the Rocky Mountains, that would be like flying from Denver to approximately where in Canada? How many miles would it have to fly to reach this Canadian location? At about what latitude would it be? (See Appendix F for further information on these exercises.) In addition, there are also a few examples of longi- tudinal migration, that is, instances where birds migrate mainly in an east-west direction. Species in which at least a part of the population does this include evening grosbeaks, California gulls, and white-winged scoters (Berger 1961). And in at least one case, Heermanns gull, the wintering region (the California coast) is north of the breeding regon (the Gulf of California). In terms of climatic variation, moving a thousand ver- Exercise #1: If in spring a bird flies from the Denver Dispersal and irruptions Migration means a regular seasonal movement to a more These terms describe other types of bird movements. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration 209 supportive biogeographic environment for the purpose of finding either suitable breeding habitat (summer) or a more reliable food supply (winter). As we have seen, migra- tion can be either horizontal or vertical. Dispersal refers to a somewhat more random move- ment at a particular time of year, most typically after the nesting season has ended and the young are now strong enough to fly on their own. This is called "post-breeding dispersal." The usual purpose of this is to find different and hopefully more abundant feeding areas for the newly expanded family. The direction of the dispersal may even be northward; many species of birds may head northward for a month or two in late summer before later heading south. Also, the nest itself is an attraction for predators; the sooner it can be abandoned, the better. Later, when the weather turns cooler and the young birds are stronger, the whole family may take part in migration, though not neces- sarily as a family group. means that in a particular year a large number of birds of a given species start showing up in locations (usually during the fall or winter) where they are normally rare or absent. One possible reason for this is an excess of younger birds in the customary breeding region. But some species, such as Lawrence's goldfinch, seem to wander irregularly for reasons that have not yet been identified. There is also the concept of an "irruption," which THE MECHANICS OF MIGRATION How far do birds migrate? migrate only a short ways, others cover huge distances. As noted above, birds that engage in vertical migration may need to travel a relatively few miles. Among the species that move southward in fall, some travel only a few hundred miles. A portion of the population of robins, There is a great deal of variation; some birds Figure 1. Black-and-white warbler (Mniotilta varia), a common migratory and breeding species over much of eastern United States and Canada. Drawing by David Stump, San Diego Audubon Society. '"$ I I I / I . y y Figure 2. Some major f lyways f o r migratory birds between Canada, the United States, and tropical America. meadowlarks, several species of sparrows, blackbirds, war- blers, and most ducks, for example, may go just from Canada and the northern tier of US. states in autumn to the Gulf Coast states, Arizona, or California. The winter range of many species, such as yellow-rumped warbler, white-crowned sparrow, Scott's oriole, white pelican, and many others, is partly in the U.S. and partly in Mexico. Some Arctic species, such as snowy owls, northern shrikes, and Bohemian waxwings, retreat southward only as far as the northern states of the US. in winter. winter and instinctively head for somewhere in tropical America. This includes most of our breeding orioles, swal- lows, flycatchers, tanagers, vireos, and warblers (Figure 1). We will look at the status of these "neotropical migrants" in more detail later on. migrants. Species such as the American golden plover, Franklin's gull, sanderling, barn swallow, bobolink, red knot, parasitic jaeger, Swainson's hawk, greater yellowlegs, and Arctic tern, may travel many thousands of miles from the United States or Canada to South America, or even far- ther. The Arctic tern, for example, breeds in the northern portions of North America, and winters as far south as islands offshore from Antarctica (USFWS 1979, 44). Their Over a hundred species, however, like it warmer in Certain species are remarkable long-distance Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 210 Pryde annual round-trip journey can be as much as 22,000 miles (about 35,000 km)! Some shorebirds, such as the surfbird and red knot, are almost equally as ambitious (Terres 1980, 604; Luoma 2001). What route do they take? dents to bird migration routes, the teacher can point out six commonly used migration corridors, called "flyways." Each of these follows an obvious physical geographic fea- ture. Two of these routes are along the Atlantic and Pacific coasts. Another common route follows the Mississippi River and its tributaries (called the Central Flyway), and a fourth follows the Great Plains, the eastern front of the Rocky Mountains, and the Rio Grande. Other easily fol- lowed routes are the Sierra Nevada and Cascade Range in the west, and the Appalachian ridges in the east (Figure 2). These migration corridors can be quite wide; birds typically migrate along a fairly broad "front," rather than along a narrow "path." corridors on a wall map of North America. Have them trace the migration route of an Arctic tern on a world map. Birds using the western and Rocky Mountain fly- ways are automatically funneled into Mexico, and from there into the narrow isthmus of Central America. Those flying down the east coast can travel from Florida to the Caribbean islands, and a few follow the Lesser Antilles all the way to South America. Some species using the Central flyway, however, prefer to fly non-stop over the Gulf of Mexico from the coast of Louisiana or Mississippi to the Yucatan Peninsula. They must store up enough fat before leaving land to sustain them while they cross the Gulf (Able 1999, ch. 4). Antilles and the Yucatan Peninsula on a world wall map. How far must a little warbler fly non-stop to go from New Orleans to Merida? American golden plover and the blackpoll warbler, ignore land altogether and fly directly across the Atlantic from eastern United States to South America (Able 1999, ch. 5; Greenberg and Lumpkin 1991). For the tiny blackpoll war- bler, this is a thousand-mile non-stop trip, an amazing feat. To do it, a favorable wind is a necessity (see below). In North America, for purposes of introducing stu- Exercise #2: Have students point out these flyway Exercise #3: Have a student locate the Lesser More remarkably, a few species, such as the Do all birds use these major flyways? six flyways mentioned above borders on over-simplifica- tion. Some types of birds (waterfowl, for example) are fairly regular in the flyway routes they use. For other species, their routes are more complex. Although many migrants may use a part of these flyways for some portion of their journey, the majority of species will head off in different compass directions at some point to zero in on their desired wintering venue or breeding grounds. A plot of the actual routes used by the various migrating species (and No; confining the topic of migration routes to the even of sub-populations within species) will show a maze of criss-crossing routes, as the birds follow age-old direc- tional patterns and landmarks that are as instinctive as the specific habitats they use for breeding. An excellent map that illustrates these complex patterns well was one that accompanied an August 1979 National Geographic article on bird migration (Fisher 1979). breed in Alaska (yellow wagtail, bluethroat, wheatear) take a southwesterly route and winter in Asia. Many Alaskan water birds head south to winter in the Aleutian Islands; some Alaskan shorebirds fly all the way to Hawaii. For at least some species, avoiding long over-water routes appears to be a fairly minor concern. Looking at a map of Middle America, you would think that the "easiest" route for eastern North America birds would be southward to Florida, a short hop to Cuba, from western Cuba to the Yucatan Peninsula, and then south (refer to Figure 2). Using this route, the longest over-water leg would only be about 160 miles (260 km). But in fact, this route is rarely used. A few birds (especially bobolinks) heading for South America, travel directly over water from Cuba or Jamaica to Colombia or Venezuela, an over-water route of about 450 miles (720 km). Many other eastern migrants fly directly from western Florida to the Yucatan, bypassing Cuba alto- gether (USFWS 1979, 69-72). It should also be mentioned that a few birds that Do birds migrate by day or night? It depends on the species, but radar studies indi- cate that most appear to migrate at night (Able 1999, ch. 2). Most insect-eating birds (wrens, warblers, flycatchers, ori- oles, vireos, thrushes, as well as most sparrows and secre- tive birds such as rails), migrate mainly by night. Species that can feed on the wing, such as swallows and nighthawks, migrate mainly by day (or at twilight), as do blackbirds, jays, waxwings, doves, and many larger birds such as hawks, cranes, pelicans, and vultures. Many species, such as swifts, herons, gulls, robins, kingbirds, ducks, grebes, hummingbirds, and others, are not particu- lar and may migrate either by day or night (Terres 1980, 605). "Think" exercise: If you were a small songbird, interested in your safety, why might you prefer to migrate at night? (Hint: Notice in the paragraph above when hawks migrate.) How do they know where they are going? The process by which birds know in which direc- tion to fly ("orientation") is a complex question that is still under investigation (Kerlinger 1995). In all probability, more than one orientation mechanism is used. Major land features such as rivers, coastlines, and mountain ranges are probably important. Birds can apparently also make use of the sun or the stars; southbound birds would know instinc- tively to keep the rising sun on their left wing, and the set- ting sun on their right. Numerous studies have shown that birds can also orient themselves on the basis of the Earth's Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration 211 magnetic field (Ambrose 2000; Weaver 2000). For those wanting more information, good summaries of research on the subject of migratory orientation can be found in Terres (1980, Migration, 606-608) or Able (1999, ch. 2). How does weather affect migration? Weather can play a role in migration in many ways. Although the birds may be aware of decreasing hours of daylight, it could be a strong cold front in September that provides the trumpet call to begin the southward movement. Major storms, of course, will delay their journey. associated with passing fronts. Migrating birds will wait (for days, if necessary) for a favorable tail wind; a head- wind could be disastrous for a small bird trying to cross the Gulf of Mexico. The locations where large numbers of migrants pause to wait for favorable weather (or to feed) are called staging areas. If there is a sudden change in wind direction, or a storm or fog develops, a fall out may occur. This means that large numbers of migrating birds will land at a convenient spot along the migration route until the winds or weather turn favorable. A late cold front might even cause a spring migrant to reverse direction and head south a ways before resuming the northward journey. Wind patterns are very important, especially those OTHER ASPECTS OF MIGRATION Do birds migrate to exactly the same spot each year? In spring, many species show great loyalty to a tra- ditional breeding territory, and in many cases will return to the exact same nest site they used previously. This is not the case in autumn; birds will usually migrate to the same general region, but they move around quite a bit within their general wintering territory. In winter, they just need to find food, and as a rule are not as territorial as they are in the breeding season. A good example is the cedar waxwing, some populations of which winter in the south- ern United States. In some winters you may see large num- bers of waxwings, and in others very few, depending on where they perceive the best food supply to be found. Of course, if the woods in which particular birds usually win- ter have been cut down, they have to look around for alter- native suitable habitat. Do they always take the same route? able, since the birds are mainly interested in finding food. In spring, the adult birds have a more specific objective, and tend to move northward in a more structured and determined manner. A few species may take a totally different return route northward in spring from that used the previous fall. A classic case of this is the American golden plover, that famous long-distance traveler. In the fall, as mentioned earlier, it may head out to sea from Nova Scotia and not touch land again until it reaches Suriname, on the way to its wintering territory in southern Brazil or northern Not necessarily. Fall migration can be quite vari- Argentina. However, the next spring, its preferred route will be to follow the Andes to Central America, cross the Gulf of Mexico, and head back to its Arctic breeding grounds via the Great Plains (Terres 1980, 603). How this pattern came about is not clear. The palm warbler, black- poll warbler, and Connecticut warbler also choose some- what different routes in the spring and the fall. Exercise #4: Have a student trace the American golden plovers two migration routes on a world map. About how many miles (kilometers) does it cover round- trip? How much fuel do you think an airliner would need to fly the same route? How high are they flying when they migrate? shown that most migrating birds are flying at 5,000 feet (1500 m) or less above the land surface, with the majority probably below 3,000 feet (900 m). However, shorebirds and waterfowl have been recorded over the Antilles as high as 22,000 feet (6700 m) (Able 1999, ch. 2). Nocturnal migrants seem to average higher flight elevations than day- time migrants (Nisbet 1963). The highest fliers may be bar- headed geese, which have been observed over the Himalayas, headed for India, at elevations near 30,000 feet (9,000 m) (Whiteman 2000). We would need supplemental oxygen to survive at that altitude; but the geese seem to do just fine. Some birds may fly high to gain stronger tail winds, or maybe just for the same reason airplanes do - less air resistance. This varies tremendously. Radar studies have How fast do they migrate? achievements are quite impressive. A lesser yellowlegs averaged 316 miles (about 500 km) a day for six straight days, a ruddy turnstone once covered 2,200 miles (3,500 km) in four days (an average of 550 miles or 880 km per day), and indigo buntings have been reported to have flown from the Yucatan Peninsula to Maine (about 2,000 miles or 3,200 km) in less than two days (Van Tyne and Berger 1976, ch. 3). Mallards have been known to cover 278 miles (445 km) in a day, Manx shearwaters over 400 miles (650 km), and white-crowned sparrows over 600 miles (1,000 km) (Welty 1982,568). Bar-headed geese may be able to cover as much as 1,000 miles (1,600 km.) in a single day (Whiteman 2000). The speed and daily range of migrants, of course, depends greatly on wind direction and velocity. Exercise #5: Have students calculate the average air speed (in miles per hour) of the white-crowned sparrow and the bar-headed goose, assuming that they fly continu- ally for the 24-hour period. This varies with the species, but some migration Do all birds of the same species migrate? sedentary local populations (sandhill cranes in Florida, for example) that do not migrate, even though the rest of the same species do. For certain other species (meadowlark, kestrel, blue jay, white-winged dove, and others), most of No, not necessarily. Some species have isolated, Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 212 Pvyde the more northern populations migrate, but the more southern ones do not. In some cases, the species is general- ly non-migratory (termed "permanent residents," or "sedentary populations"), but the very northernmost popu- lations may move south ("withdraw") a short distance to escape a hard winter at the northern fringe of their range. Examples of species that do this include various species of crow, black phoebe, and phainopepla. Are migration patterns permanent? birds are adaptable, and over time they may alter their migratory habits to reflect changes in climate or vegetation cover. An example is the Scott's oriole, which used to be seen in the southern California deserts only in spring and summer. Now a small number winter regularly in California's Anza-Borrego Desert State Park. As the North American climate gets warmer, the trend of birds wintering in more northern locations may continue. Not necessarily. As with many things in nature, Do birds in the Southern Hemisphere migrate north in the winter? Yes, if they need to. For example, many species of penguins would be unable to survive the harsh Antarctic winter, and so they migrate (by swimming!) to the Falkland Islands or other more temperate locations for the duration of the Austral fall and winter (that is, April to September). Because there are relatively few land masses between 40 and 60" south latitude, migrations in the Southern Hemisphere involve far fewer birds than in the Northern Hemisphere. Exercise #6: Have students locate the Antarctic Peninsula and the Falkland Islands on a world map, and determine how far the penguins have to swim. What's the name of the body of water they cross? Do the coastal areas along the Antarctic Peninsula freeze over in winter? Be sure the students know: What are the winter months in Antarctica? MIGRATION AND HABITAT It has been noted that many species of migratory birds appear to be diminishing in numbers in all or part of their range; regionally significant declines in at least 107 species of neotropical migrants have been documented (DeGraaf and Rappole 1995, 23). At least 13 of these are endangered. Typically, populations of most species are regionally variable, with numbers increasing in some parts of their range and decreasing in others (Peterjohn et al. 1995). In order to understand net decreases in a species' populations, all three areas of their life cycle - breeding grounds, wintering grounds, and migration routes - must be examined. How important is the preservation of breeding areas? cal. The loss of tropical forests is a major problem for migrating songbirds, but for many species the loss of Maintaining the viability of breeding areas is criti- breeding habitat in North America may be a worse threat. The main reason for this is that many species of birds are very fussy about where they nest. As mentioned earlier, wintering birds are more apt to be "footloose" (that is, will- ing to explore new areas for finding food) than are breed- ing birds. Many species require a specific type of breeding habitat, and will not nest in any other. California gnat- catchers breed only in coastal sage scrub, spotted owls require old growth conifer forests, grasshopper sparrows need particular types of grasslands, snowy plovers need sandy ocean beaches, and Kirtland's warblers nest only in young jack pines. It would be great if all our breeding birds could be more adaptable, in the manner of mourning doves, ravens, mockingbirds, and house finches. But for many species, that is not their nature. For the "fussier" species, we either preserve traditional breeding habitat, or we risk losing many of our migratory birds. Is loss of tropical forests a major problem for migrating birds? pace of forest destruction in tropical American countries (and elsewhere in the world as well). The loss of biodiversi- ty that is resulting is of great concern in terms of the potentially valuable genetic information we may be losing. In the process, large areas of wintering habitat for migrato- ry songbirds are being lost as well (Terborgh 1989). This unfortunate trend is partially mitigated by the fact that, although half of all tropical forests have disap- peared in the last fifty years, the number of migrating song birds has dropped in the same period by a smaller percent- age. Thus, as an overall generalization, there is almost as much winter habitat per bird as there was in the mid-twen- tieth century, despite loss of forests, because the total num- bers of migrating birds have been so greatly reduced. Of course, loss of particular areas of tropical forests may itself be a causal factor in the reduction in numbers of certain species of neotropical migrants. In general, the remaining tropical forests are not overcrowded with North American migrants. In most tropi- cal forests today, migrants make up a fairly small percent- age of the winter bird population. This is more the case the farther south you go; Mexico, for example, hosts 189 species of North American migrants, Costa Rica 69, Brazil 25, and Bolivia only 18 (Rich 1998). Many species may tend to inhabit forests edges rather than interior forests (Karr 1976). Overall, our knowledge of North American migrants while in the tropics is fairly poor, and it is often difficult to establish exactly where a particular population of birds is wintering (Berger 2000). For more information on North American migrants in the tropics see Rappole (1995) and DeGraaf and Rappole (1995). However, it was noted earlier that many species of North American birds winter north of the tropics, a few largely within the United States. Even here, wintering habi- tat is far from secure; as just one example, California's Salton Sea, home to millions of wintering water and shore Yes, a great deal has been written about the rapid Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration birds, is seriously threatened. 213 APPENDIX A Classroom Exercise How important is the condition of their migration route? Very, especially for birds that make frequent stops. And, unfortunately, conditions are deteriorating. We know that millions of migrating birds never make it to their win- tering grounds, due to technological hazards, such as radio towers and guy wires, and urban lights which disorient them (Malakoff 2001; Stangel 2002). Migration is a stress- ful and exhausting process, and at whatever point birds must stop to rest, there must be suitable habitat and food at those locations. When we cut forests, drain lakes, and channelize wetlands, we eliminate these expected rest stops: and make migration all that much more difficult. Maintaining quality habitat is particularly important at those locations, for example, where migratory birds make landfall after a long marine crossing. What will be the effect of global warming? It is likely that global warming, if it continues, will also greatly affect the ability of birds to breed. Average temperature changes of a few degrees per se may not be too important for nesting birds, but changes in precipitation patterns induced by temperature variations could be very significant (Solomon and Cramer 1993). Global warming will affect length of growing sea- son, amounts of soil moisture, and regional precipitation patterns, increasing these in some areas, decreasing them in others. In areas with less rain, for example, trees may bear less fruit, grasslands could become less productive, or certain insects used for food might be less plentiful. Thus, competition for food could become more intense, or par- enting birds might have to fly farther to find it. In such instances, they might be able to raise only one chick instead of two, or in extreme cases, none. Conversely, in some locations climatic change might benefit certain species. birds and the difficulties they are facing, various agencies have cooperated to create the annual International Migratory Bird Day, usually celebrated the second Saturday in May. Contact a local office of the U.S. Fish and Wildlife Service or the Audubon Society to see if any special activi- ties are being planned in your community to celebrate the next International Migratory Bird Day, and consider how the elementary school children in your classes might take part in them. To help publicize the importance of migratory This exercise will familiarize students with several families and species of migrant North American birds, help them to identify their likely migration routes, acquaint them with the states, provinces, regions and countries of North, Middle, and South America, and assist in developing their mapping skills. In this classroom exercise (or homework exercise, for older students), each student will select a particular bird species that appeals to them from Appendix A.l. The student will then look up the species in any standard field guide to North American birds (see Bibliography), and pre- pare a color sketch of it. Note that for some species, there may be a difference between male and female plumage. They could draw both, if they wished. map in Appendix A (Figure 3) available for each student. On their copy of this map, have the student sketch in their birds breeding regon, as well as the country, countries, or parts of one or more countries where it winters, as indicat- ed in the table in Appendix A.l. Ask them to indicate by means of a curved arrow the most likely migration route (or routes) this species might use. (Suggestion: read to them the paragraphs in the text sections entitled What route do they take? and How do they know where theyre going? and suggest they look for north-south rivers, coasts, mountain ranges, islands, and other landforms, sit- uated along or near the route that they might possibly fol- low). A sample map, using the black-and-white warbler as an example, is illustrated in Figure 4 (see also Figure 2). If you would like them to do a little additional map investigation, you could ask them to list some of the states, or major cities, that they might fly over (or rest in) along their migration route. The instructor should have copies of the outline Additional classroom exercise: If the teacher, or other personnel at your school, has some familiarity with local birds, during spring and fall migration, you could have the students compile a list of the migratory birds they see around the schoolyard, or at home (you may have to help them a bit with species identification). keeping a separate list of birds seen before the migration season starts (i.e., in mid-winter or late summer). Having a bird feeder outside the classroom, if feasible, would help. Start by Additional exercise: Contact a local Audubon Society, nature center, or similar organization, and inquire what kinds of native vegetation you could plant around your home or school that would attract migratory birds. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 214 Pryde 0 500 1000 miles 0 500 1000 2000 km - 'igure 3. Outline map to use with the classroom exercise (Appendix A). Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration 215 0 500 1000 miles 0 500 1000 2000 km - Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 216 APPENDIX A . l - FORTY SELECTED NORTH AMERICAN MIGRATORY SPECIES Pryde Species Eared grebe Upland sandpiper Greater yellowlegs Mississippi kite Broad-winged hawk Royal tern Burrowing owl Olive-sided flycatcher Scissor-tailed flycatcher Red-eyed vireo Violet-green swallow Putple Martin Wood thrush Sage thrasher Golder-winged warbler Chestnut-sided warbler Black-andwhite warbler Black-throated blue warbler Blackburnian warbler Hermit warbler Kirtlands warbler Palrn warbler McGillivray's warbler Hooded warbler Northern waterthrush Yellow-breasted chat American redstart Red-faced warbler Scarlet tanager Western tanager Lark sparrow Golden-crowned sparrow Green-tailed towhee Chestnut-collared longspur Rose-breasted grosbeak Diskcissel Lazuli bunting Bobolink Orchard oriole Common redpoll Breeding area (a) Saskatchewan, North Dakota North Dakota, Manitoba n. Ontario, n. Quebac s. Mississippi, Louisiana New York, New England states Gulf and Alantic states' coasts Wyoming, Montana Washington, British Columbia Oklahoma,Texas Tennessee, Kentucky Nevada, Utah New York, Vermont Indiana, Ohio Wyoming, w. Colorado Michigan, Wisconsin New York, s. Ontario Kentucky, West Virginia Maine, s. Quebec New Hampshire, Maine w. Oregon, n. California n. Michigan (only) n. Alberta, n. Saskatchewan Utah, Idaho Alabama, Georgia Alaska, Yukon Arkansas, Tennessee Montana, Alberta Arizona, New Mexico Ohio, Pennsylvania Oregon, Idaho Kansas, Nebraska s.Yukon, British Columbia Colorado, New Mexico North Dakota, e. Montana New York, Ontario Missouri, Kansas California, Oregon South Dakota, Minnesota Virgnia, N. and S. Carolina Alaska, Yukon Wintering area (a) s. New Mexico and Texas, n. Mexico Paraguay, s. Brazil Florida, West Indies e. Bolivia, sw. Brazil Brazil, Suriname Cuba, Jamaica, Haiti s. Texas, n. Mexico Andes Mtns., Columbia to Peru s. Mexico, Guatemala e. Columbia, e. Peru s. Mexico, Belize w. Brazil, e. Bolivia Honduras, Nicaragua w. Texas, n. Mexico Costa Rica, Panama Nicaragua, Costa Rica Yucatan, Guatemala Jamaica, Puerto Rico Ecuador, n. Peru Honduras, El Salvador Bahamas Florida, Cuba s. Mexico, Guatemala Belize, Yucatan peninsula Columbia, Venezuela se. Mexico, Belize Guatemala, Honduras Guatemala, El Salvador Ecuador, n Peru s. Mexico, s. Guatemala s.Texas, n. Mexico California, n.Baja California s.Arizona, Mexico (all) w. Texas, n. central Mexico Panama, Columbia Venezuela, n. Guyana w. Mexico e. Bolivia, e. Paraguay Coata Rica, Nicaragua Manitoba, North Dakota (a) For each species, one or two typical breeding and wintering states, provinces, or countries are given. It would be too cornplex to try to describe each species' entire breeding and wintering ranges. Abbreviations: n.= northern; e.= eastern; s. =southem; w.= western; se.= southeastem, etc. Sources: Terres; US. Fish & Wildlife Service; "No Place to Land"; Dunn and Garrett. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration 217 APPENDIX B Recommended Field trip Organize a field trip to a local nature preserve, or other suitable habitat, during late April - May, or during September - October, to look for migrants. Many urban areas have a privately operated nature preserve or a national wildlife refuge nearby where guided tours, or knowledgeable individuals, may be available. Contacting the nearest chap- ter of the Audubon Society is often a good way to get information about local nature preserves. Be sure to take at least one of the recommended field guides with you on the field trip (see Bibliography). Have at least one pair of binoculars with you on the trip, and preferably several pairs. Younger students will need help using them; it is not instinctively obvious to a child how to locate a bird in a tree through binocular lenses, or how to focus them. Having students wear baseball-style caps on the field trip will help avoid glare from the sun and make it easier to see birds. Long pants and appropriate footwear are also recommended. Depending on your location, you may want to have insect repellant or sunscreen available. Be sure you know if your school or district requires parental permission for field trips. APPENDIX C Materials needed for this curriculum module 6 Any field guide to North American birds (the National Geographic [3rd edition, 19991 field guide, and those by Kenn Kaufman [2000] and David Sibley [2000] are the most recent and informative - see the Bibliography). Outline maps of North America and the Western Hemisphere (or, simply reproduce the map in Appendix A). A wall map of the Western Hemisphere, or of the world. Desirable: Several pairs of binoculars for the field trip. Be sure to have at least one pair. A spotting scope would be even better, especially for younger children, if its possible to borrow one. * Additional references: If the teacher desires additional general reference works on birds, three recommended books are those by Attenborough (1998), Kaufman (1996), and Kress (2000) as listed in the Bibliography. The Los Angeles Audubon Society bookstore stocks numerous books for children on bird topics, as well as electronic resources (videos, CD-roms, etc.); they can be contacted at 323-876-0202 or APPENDIX D ONE-PAGE READING ASSIGNMENT (GRADES 4 - 6) Many birds that nest in the United States and Canada fly south to warmer regions to spend the winter. Then, the next spring, they fly north once again to return to their breeding grounds. This movement of birds twice a year is called migration. Northward migration in the spring occurs mainly from mid-March to mid-May. migration occurs mainly during the months from August to October. In the fall, southward Some birds travel only a short distance and winter in the southern part of the United States, but a few go all the way to South America. Most species of migrating birds winter somewhere in between, for example, in Mexico, Central America, or the islands of the Caribbean Sea. The main reason that birds migrate is not so much because of cold weather; rather it is more because food sup- plies become scarce in winter. Some birds that have a secure source of food in the winter do not need to migrate. When they migrate, birds often follow obvious physical features, such as coastlines, mountain ranges, and rivers. The routes that are most frequently used are called flyways, but migrating birds may go in other directions as well. In migration, they may also be able to tell direction by the location of the sun, or even the stars. They also may be able to follow the earths magnetic field, as though they had a built-in compass. The total numbers of many species of birds have decreased during the past forty years. This is mainly because much of the habitat they use, both in winter and summer, has been lost to bigger cities, new farms, forest loggng, and mining operations. Also, there are many new hazards that they encounter along their migration route, such as tall struc- tures and transmission lines, which human beings have created. We must be more careful that we are not accidentally preventing birds from successfully migrating. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 218 Pryde APPENDIX E Glossary Austral Relating to the Southern Hemisphere, especially its more southern portions. Biome Boreal Dispersal Refers to a major plant-animal community such as tundra, tallgrass steppe, temperate rainforest, etc. Relating to the sub-Arctic; boreal forests are the conifer-dominated forests of central Canada and Alaska. Random seasonal movements by some birds, usually following nesting and before starting migration. Fall-out A temporary rest stop by migratory birds, usually either to feed or to wait out unfavorable weather. Irruption Migration A route used by large numbers of birds during migration; typically along north-south rivers, coasts, mountains, etc. An irregular movement of significant numbers of a particular bird species to a different location than what is customary. The regular seasonal movement of birds or other animals to more hospitable locations, usually to find a better food supply. Neotropical migrant A bird that migrates from the cooler portions of the United States and Canada to more tropical regons of southern Mexico, the Caribbean, and Central and South America. Passerine A large order of birds that are often referred to as song birds or perching birds. Raptor A bird of prey (meat-eaters), including hawks, eagles, falcons, osprey, owls, etc. Riparian Pertaining to streams; stream-side vegetation used by birds is termed riparian habitat. Sedentary Non-migratory. Said of birds that are permanent residents of a given regon. Staging area Locations where birds congregate to feed, or to await favorable weather conditions for migrating Tundra The open, treeless region adjacent to the Arctic Ocean. High mountain areas above the tree line are alpine tundra. Vertical migration Seasonal movement up and down mountain ranges, usually to higher elevations in summer and lower ones in winter. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography of Bird Migration APPENDIX F Teachers Guide to the In-Text Exercises 219 Exercise #1: 4,000 vertical feet equals approximately 1,200 miles (1930 km) northward. 1,200 miles north of Denver would be a little north of Edmonton, Alberta. Exercise #2: The autumn route of the arctic tern can be simplified to extend southward from Alaska past Canada, the United States, Mexico, Central America, and on to the tip of South America, following an off-shore route. Then have the students trace the return route in the spring. Exercise #3: New Orleans to Merida is about 650 miles (1,050 km). Exercise #4: a. Use the description of the American golden plovers route given in the b. From Nova Scotia to Buenos Aires is about 5,600 miles (9,000 km) each c. No need for precision here - it would obviously depend on the size of the preceding paragraph to guide the student(s) working at the map. way, or about 11,000 miles (18,000 km) round trip. airliner. For young children, a response of tons and tons conveys the desired point adequately. Exercise #5: - White-crowned sparrow: 600 miles (1,000 km) a day equals a nonstop average - Bar-headed goose: 1,000 miles (1,600 km) a day equals a nonstop average of of about 25 mph (42 km/hour). about 42 mph (67 km/hour). Exercise #6: a. From the Antarctic Peninsula to the Falkland Islands is about 800 miles, or 1,300 kilometers. b. The Drake Passage, which is famous for high winds and huge waves. c. Yes. d. May, June, July, August and September. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 220 Pryde AJTENDLX G Bibliography Kaufman, K. 1996. Lives of North American Birds. Boston: Houghton-Mifflin. [gives information beyond what appears in field guides for all North American bird species] Able, K. P. 1999. Gatherings of Angels: Migrating Birds and Their Ecology. Ithaca, NY Comstock Books. [Good summary, not too technical] Kaufman, K. 2000. Birds of North America. New York: Houghton-Mifflin. [Field guide] Ambrose, S. G. 2000. Built-in compass may steer animals direction, Sun Diego Union-Tribune, August 9, F-5. Kerlinger, P. 1995. How Birds Migrate. Mechanicsburg, PA: Stackpole Books. Attenborough, D. 1998. The Life of Birds. London: BBC Books. [the life-styles of birds] Kress, S. W. 2000. National Audubon Society Birders Handbook. London: Dorling-Kindersley. [chapters cover a wide range of topics for beginning and experienced birders] Berger, A. J. 1961. Bird Study. New York: John Wiley. [Chapter 4 is one of the earlier comprehensive dis- cussions of migration] Berger, C. 2000. Exposed: Secret lives of warblers, National Wildlife 3: 46-53. Luoma, J. R. 2001. The removable feast, Audubon 3: 48-54. [On migration of red knots] Cruickshank, H. G., ed. 1957. John and William Bartrams America: New York: The Devin-Adair Co., 300-311. Malakoff, D. 2001. Faulty towers, Audubon 5: 78-83. [On modern migration hazards] DeGraaf, R. M., and J. H. Rappole. 1995. Neotropical Migratory Birds. Ithaca: Comstock Publishing Associates. [summarizes the status of 361 species of migrants] Martin, T. E., and D. M. Finch, eds. 1995. Ecology and Management of Neotropical Migratory Birds. New York: Oxford University Press. Mead, C. 1983. Bird Migration. Feltham, UK: Country Life Books. [Lots of maps!] Dunn, J., and K. Garrett. 1997. Warblers. Boston: Houghton Mifflin. [Specialized guide] National Geographic Society. 1999. Field Guide to North American Birds, 3rd ed. Washington, DC: National Geographic Society. [A standard field guide] Elphick, J., ed. 1995. Atlas of Bird Migration: Tracing the Great Journeys of the Worlds Birds. New York: Random House. [describes both Old and New World migrations] Nisbet, I. C. T. 1963. Measurements with radar of the height of nocturnal migration over Cape Cod, Massachusetts, Bird Banding 34: 57-67. Field, J. T. F. 2000. Ten Early American Ornithologists. San Diego: Vanard Lithographers. No Place to Land. 1994. Map illustrating bird migration, prepared by the Nation Audubon Society, New York, NY. [Unfortunately, out of print] Fisher, A. C., Jr. 1979. Mysteries of bird migration, National Geographic 2: 154-193. Greenberg, R., and S. Lumpkin. 1991. Birds Over Troubled Forests. Washington, DC: Smithsonian Institution. Peterjohn, B. G., J. R. Sauer, and C. S. Robbins. 1995. Population trends from the North American breed- ing bird survey, in T. E. Martin, and D. M. Finch, eds., Ecology and Management of Neotropical Migratory Birds. New York: Oxford University Press, 3-39. Hagan, J. M., and D. W. Johnston, eds. 1992. Ecology and Conservation of Neotropical Migrant Landbirds. Washington, DC: Smithsonian Institution Press. Jaeger, E. C. 1948. Does the poorwill hibernate? Condor 1: 45-46. Rappole, J. 1983. Nearctic Avian Migrants in the Neotropics. Washington, DC: U.S. Fish and Wildlife Service. Karr, J. R. 1976. On the relative abundance of migrants from the north temperate zone in tropical habitats, Wilson Bulletin 88: 433-458. Rappole, J. 1995. The Ecology of Migrant Birds. Washington, DC: Smithsonian Institution Press. Rich, T. 1998. The marvel of migration, Birders World, June, 20-23. Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013 The Geography o f Bird Migration 221 Sibley. D. 2000. The Sibley Guide to Birds. New York: A. A. Knopf. [Field guide] Solomon, A. M., and W. P. Cramer. 1993. Biospheric implications of global environmental change, in A. M. Solomon, and H. H. Shugart, eds., Vegetation Dynamics and Global Change. New York: Chapman and Hall, 25-52. Stangel, P. 2002. Call 911! Wild bird 1: 54-60. [On hazards to migratory birds posed by communications towers] Terborgh, J. 1989. Where Have All the Birds Gone? Princeton, NJ: Princeton University Press. [mainly on declining numbers, habitats, and deforestation] Terres, J. K. 1980. The Audubon Society Encyclopedia of North American Birds. New York: Alfred Knopf, S.V. Migration, 602-608. [The most extensive reference work available] U.S. Fish and Wildlife Service (USFWS). 1979. Migration of Birds (Circular 16). Washington, DC: Department of the Interior. Van Tyne, J., and A. J. Berger. 1976. Fundamentals of Ornithology, 2nd ed. New York: Wiley. [Standard textbook on ornithology - see especially pp. 333- 380 on migration] Weaver, J. C. 2000. Biological sensing of small field differences by magnetically sensitive chemical reactions, Nature 6787 707-709. Weidensaul, S. 1999. Living on the Wind: Across the Hemisphere with Migratory Birds. New York: North Point Press. [Uses a more informal writing style] Welty, J. C. 1982. The Life of Birds, 3rd ed. Philadelphia: Saunders College Publishing. Whiteman, L. 2000. The high life, Audubon 6: 104-8. [On how high birds fly] Downloaded by [University of Missouri Columbia] at 20:34 17 March 2013