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, UK

    Journal of GeographyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/rjog20

    The 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, 207-221

    To link to this article: http://dx.doi.org/10.1080/00221340208978501

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  • 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

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    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 ma

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