Chapter IV: Introduction: 2 (4)

Graber concluded from radar observations that the disparity in seasonal flight directions of many migrants was a positive response of migrants to favorable wind directions at that time of year. The east-oriented trans-gulf migrants followed an elliptical migration because postfrontal air flow in the fall at latitude 40° N is northwesterly, and, in the spring southerly; whereas winds over the Gulf of Mexico are consistently easterly or southeasterly. Therefore, transgulf migrants returning north in the spring would be moved westward across the Gulf unless they compensated for wind drift. Observers were not aware of high-altitude drift before radar (Bellrose and Graber 1963).

Numerous other loop migrations have been documented throughout the world. In the fall, the short-tailed shearwater, is observed off the west coast of North America as far south as California. At this time the species is on the eastern leg of a tremendous figure-eight circuit around the Pacific Ocean (Fig. 26). The subalpine warbler and red-backed shrikes perform loop migrations between Europe and Africa. Both pass much farther to the east in the spring than in the fall (Moreau 1961). The Arctic loon travels south across inland Russia to southern Europe but returns to its Arctic breeding grounds via the Gulf Stream on the sea because this water is open much earlier in the spring than the inland waterways (Welty 1962).

Dog-legs

Dog-leg migration patterns are characterized by a prominent bend or twist in the route. Studies have shown some of these illogical, out-of-the-way means for connecting wintering and breeding areas have no biological function, but instead, are the result of tradition much like the lineage of crooked streets in Boston can be traced back to old cowpaths (Welty 1962). Many species have extended their range in recent years, but the pioneers continue to retrace the old route from the point of origin even if the new areas are not on the same axis as the earlier route. The old pathways have apparently become implanted as part of the migratory instinct in all members of particular populations even after extending their ranges considerable distances from the original.

Good examples of this crooked traditional path can be seen in the routes taken by Old World species extending their ranges into the New World from Europe and Asia. The European wheatear has extended its range into Greenland and Labrador where the local breeding population has become a separate race. When the Labrador individuals depart from their breeding grounds, they proceed north to Greenland, their ancestral home, then west to Europe and south to Africa, the traditional wintering area for all wheatears. Alaskan breeding wheatears migrate to Africa in the opposite direction via Asia where the Alaskan population presumably originated. Alaskan breeding Arctic and willow warblers and bluethroats also migrate westward into Siberia and then southward on the Asiatic side. Some investigators believe the Arctic tern colonized the New World from Europe because when this bird departs for the south it first crosses the Atlantic to Europe, then moves down the eastern Atlantic coast to Africa and either back across the Atlantic to South America or continues south down past South Africa (Fig. 11). To get to South America from the eastern Arctic, it would be shorter to follow the golden plover's flight path straight down the Atlantic or along the east coast of the United States but the fact that no Arctic terns have been observed in the Caribbean indicates that they do no follow that route.

In western United States, California gulls nest in various colonies around Great Salt Lake and Yellowstone Park. Banding records indicate these populations winter along the California coast (Fig. 27). Instead of traveling southwest by the shortest distance to the wintering grounds, they proceed longitudinally down the Snake and Columbia Rivers and reach the coast around Vancouver ( Woodbury et al. 1946). Thence they proceed south along the coast to Oregon and California. In the spring the adults return over the same course rather than taking the shorter flight northeast in April across the deserts and mountains; this route would be largely made over a cold and inhospitable country (Oldaker 1961).

Sladen (1973) has mapped the migration routes of whistling swans, and several dog-leg patterns are apparent in the eastern and western populations (Fig. 28). In the eastern population, a sharp change in direction occurs at their major feeding and resting areas in North Dakota. After the birds arrive from the Arctic breeding grounds, they proceed east-southeast to their wintering grounds on Chesapeake Bay. In the western population, thousands of birds migrate from the Alaskan breeding grounds to the large marshes along Great Salt Lake. Then after a major stopover, this population heads west over the mountains to California.

Pelagic Wandering

Many of the pelagic birds observed off our coasts or at sea appear to be nomadic when they are not breeding. These movements are not necessarily at random because there is usually a seasonal shift in the population, often for great distances and in specific directions, away from the breeding area after completion of the nesting cycle. Also the return from the sea to nesting areas is at a definite time of year. This may not be true migration in the classical sense (Thomson 1964), although it is similar in most respects.

Because of the extensive and often inhospitable habitat of pelagic birds (to human observers at least), observations on their movements are difficult at best and accurate records are few. We do know some of these species have regular routes (e.g., Arctic terns) and specific patterns of migration (e.g., the loop in the short-tailed shearwater). As more knowledge is accumulated on the "nomadic" species, we may actually find they too have regular migration routes based on biological needs.

Movements of some of the tubenoses (Order Procellariiformes, that includes albatrosses, fulmars, shearwaters, and petrels) have been correlated with ocean currents, prevailing winds, temperatures, and general water fertility (Kuroda 1957; Shuntov 1968; Fisher and Fisher 1972). Commercial fishermen have long known ocean currents are very important factors in the supply of nutrients, plankton, and forage fish for larger fish. These same foodstuffs often attract pelagic birds as evidenced by the tremendous concentrations that occur off the Peruvian coasts where the upwelling of cold nutrient-bearing water is evident. Kuroda (1957) found some fine correlations between the route of the short-tailed shearwater and ocean currents. Likewise Shuntov (1968) found the migratory routes of albatrosses were over temperate marine waters of high biological productivity. The Laysan albatross was correlated with cold currents, while the black-footed albatross occurred over warm currents. Many Southern Hemisphere pelagic species have been extremely successful in exploiting rich northern waters during the summer; the group is probably the most abundant and widespread in the world (Bourne 1956).

Leap-frogging

When two or more races of the same species occupy different breeding ranges on the same axis as migratory flight, the races breeding the farthest north often winter the farthest south. Thus, a northern race "leap-frogs" over the breeding and wintering range of the southern populations. This has been well documented in the fox sparrow discussed previously (Fig. 10) and is exhibited by races of Canada geese breeding in central Canada as well. One of the smaller races of this goose breeds along the Arctic coast of the Northwest Territories and winters on the Gulf coast of Texas and northeastern Mexico, while a much larger race breeds in the central United States and Canada but winters in the central part of the United States. This leaping over occurs in other species as well, including the bluebird (Pinkowski 1971).

Vertical Migration

In the effort to find winter quarters furnishing satisfactory living conditions, many North American birds fly hundreds of miles across land and sea. Others, however, are able to attain their objectives merely by moving down the sides of a mountain. In such cases a few hundred feet of altitude corresponds to hundreds of miles of latitude. Movements of this kind, known as "vertical migrations," are found worldwide wherever there are large mountain ranges. Aristotle first mentions vertical migration: "Weakly birds in winter and in frosty weather come down to the plains for warmth, and in summer migrate to the hills for coolness ..." (Dorst 1962). The number of species that can perform this type of migration pattern is obviously limited to those species adapted to breeding in alpine areas.

In the Rocky Mountain region vertical migrations are particularly notable. Chickadees, rosy finches, juncos, pine grosbeaks, Williamson's sapsuckers, and western wood pewees nest at high altitudes and move down to the lower levels to spend the winter. The dark-eyed juncos breeding in the Great Smoky Mountains make a vertical migration, but other members of the species, breeding in flatter areas, make an annual north-south migration of hundreds of miles (Van Tyne and Berger 1959). There is a distinct tendency among the young of mountain-breeding birds to work down to the lower levels as soon as the nesting season is over. The sudden increases among birds in the edges of the foothills are particularly noticeable when cold spells with snow or frost occur at the higher altitudes. In the Dead Sea area of the Middle East, some birds that breed in this extremely hot desert move up into the surrounding cooler hill during the winter (Thomson 1964).

The vertical migrations of some mountain dwelling gallinaceous birds (mountain quail and blue grouse) are quite interesting because the annual journey from breeding to wintering grounds is made on foot. Mountain quail make this downward trek quite early in the fall well before any snows can prevent them from reaching their goal. Blue grouse perform essentially the same journey in reverse. During midwinter, these birds can be found near timberline eating spruce buds protruding above the snow.

These illustrations show that the length and direction of a migration route are adapted to the needs for survival and are met in some cases by a short vertical movement or great latitudinal travels in others.

Pre-migratory Movements

Recent banding studies have demonstrated many migrants, especially young of the year, have a tendency to disperse after fledging. These premigratory movements have also been called "post-fledging dispersal," "reverse migration," and "postbreeding northward migration." Demonstration of this phenomenon is especially important as it relates to locality-faithfulness (Ortstreue), range extension, and gene mixture between populations. These movements cannot be considered as true migrations even though they are repeated annually by the species between breeding grounds and some other area. These movements are generally repeated by the same age class in the population but not the same individuals.

Nevertheless, these regular northward movements are quite striking, especially in herons. The young of some species commonly wander late in the summer and fall for several hundred miles north of the district in which they were hatched. Young little blue herons as well as great and snowy egrets are conspicuous in the East as far north as New England and in the Mississippi Valley to southeastern Kansas and Illinois. Black-crowned night herons banded in a large colony at Barnstable, Massachusetts, have been recaptured the same season northward to Maine and Quebec and westward to New York. In September most of them return to the south.

These movements have been noted in several other species as well. Broley (1947) nicely illustrated this northward movement of bald eagles along the Atlantic coast (Fig. 29). Birds banded as nestlings in Florida have been retaken that summer 1,500 miles away in Canada. Van Tyne and Berger (1959) surmised the summer heat of Florida was too great for this eagle, a northern species that has only recently spread into Florida to take advantage of abundant food and nesting sites, which it exploits during the cooler season. Postbreeding northward movements are also shared by wood ducks, yellow-breasted chats, eastern bluebirds, and white pelicans.

A somewhat different type of postbreeding migration is the so-called "molt migration" exhibited by many species of waterfowl (Salomonsen 1968). These birds may travel considerable distances away from their nesting area to traditional molting sites where they spend the flightless period of the eclipse plumage. At such times they may move well into the breeding ranges of other geographic races of their species. These movements may be governed by the availability of food and are counteracted in fall by a directive migratory impulse that carries those birds that attained more northern latitudes after the nesting period, back to their normal wintering homes in the south.

Vagrant Migration

The occasional great invasions beyond the limits of their normal range of certain birds associated with the far North are quite different from migration patterns discussed previously. Classic examples of such invasions in the eastern part of the country are the periodic flights of crossbills. Sometimes these migrations will extend well south into the southern States.

Snowy owls are noted for occasional invasions that have been correlated with periodic declines in lemmings, a primary food resource of northern predators. According to Gross (1947), 24 major invasions occurred between 1833 and 1945. The interval between these varied from 2 to 14 years, but nearly half (11) were at intervals of 4 years. A great flight occurred in the winter of 1926-27 when more than 1,000 records were received from New England alone, but the largest on record was in 1945-46 when the "Snowy Owl Committee" of the American Ornithologists' Union received reports of 13,502 birds, of which 4,443 were reported killed. It extended over the entire width of the continent from Washington and British Columbia to the Atlantic coast and south to Nebraska, Illinois, Indiana, Pennsylvania, and Maryland. One was taken as far south as South Carolina.

In the Rocky Mountain region, great flights of the beautiful Bohemian waxwing are occasionally recorded. The greatest invasion in the history of Colorado ornithology occurred in February 1917, when it was estimated that at least 10,000 were within the corporate limits of the city of Denver. The last previous occurrence of the species in large numbers in that section was in 1908.

Evening grosbeaks likewise are given to more or less wandering journeys, and, curiously enough, in addition to occasional trips south of their regular range, they travel east and west for considerable distances. For example, grosbeaks banded at Sault Ste. Marie, Michigan, have been recaptured on Cape Cod, Massachusetts, and in the following season were back at the banding station. Banding records and museum specimen identifications demonstrate that this east-and-west trip across the northeastern part of the country is sometimes made also by purple finches, red crossbills, and mourning doves.

=ORIGIN AND EVOLUTION OF MIGRATION=

The origin and evolution of bird migration has been discussed in ornithological literature for centuries. As we have seen from the foregoing discussion, migration exists in many forms throughout the world and probably arose to satisfy many different needs in different orders of birds at the same time. New pattens, traditions, and routes are arising today as well as disappearing. Currently, the migration patterns we see are a composite result of historic influences mixed with present day influences. Even though the migration of several different species may be very similar, the patterns exhibited today can be the result of quite different evolutionary processes. Because it cannot be substantiated by experimental facts, any explanation of how a particular pattern or route originates is pure conjecture.

The general anatomical and physiological attributes of birds enable them to develop more diverse and spectacular migratory behavior than any other group of animals. Their potential for long sustained flights is of primary importance in pre-adapting birds to successful migrations. Migration has long since become a definite hereditary habit of many species of birds that recurs in annual cycles, evidently because of physiological changes which prompt a search for an environment suitable for reproduction and survival. Like the bird's other habits its migratory behavior is just as characteristic as the color of its plumage and, like it, evolved through natural selection because it was advantageous for the survival of the population. Its origin has been thought by some to be a mystery locked in past ages, but by study of the history of how birds came to occupy their present ranges, information becomes available which suggests theories that may be developed and explored. Two that are commonly mentioned are termed the "Northern Ancestral Home Theory" and the "Southern Ancestral Home Theory."

According to the former of these hypotheses, in earlier ages when conditions of climate, food, and habitat were favorable for existence of birds throughout the year much further north than is the case today, many species remained in these northern latitudes as permanent residents. Today, such conditions are found only in more southern regions where migrations are much shorter or nonexistent. Gradually, however, in the Northern Hemisphere the glacial ice fields advanced southward, causing a southward movement of conditions favorable to northern birds, until finally all bird life was confined to southern latitudes. As the ages passed, the ice cap gradually retreated, and each spring the birds whose ancestral home had been in the North moved in again to fill newly opened breeding habitat only to be driven south again at the approach of winter. As the size of the ice-covered area diminished, the journeys to the summer breeding areas became even longer until eventually the climatic conditions of the present age became established, and with them, present patterns of the annual advance and retreat we call migration.

The opposing theory is simpler in some respects and supposes the ancestral home of Northern Hemisphere migratory birds was in the Tropics. As all bird life tends to overpopulation, there was a constant effort of young individuals to pioneer and seek breeding grounds where competition was less severe. Species better adapted to more northern latitudes moved in that direction for nesting but were kept in check by the glacial ice and forced to return southward with the recurrence of winter conditions. Gradually, as the ice retreated, vast areas of virgin country became successively suitable for summer occupancy, but the winter habitat in the South remained the home to which the birds returned after the nesting season.

The above two theories presume that the Quaternary glaciations, which occurred 10,000 to 1 million years ago, have been the predominate influence on bird migration in North America and Europe as we observe it today. There is no doubt these extreme climatic and ecologic barriers played a part in shaping or modifying some patterns, but as Moreau (1951) has pointed out, well-developed migrations occur in parts of the world, including the Southern Hemisphere or even within the tropics, where continental glaciation was not a factor. Furthermore, migrations to fit various needs have probably been going on ever since birds could fly. The tremendous Pleistocene glaciations actually occupied less than a hundredth of the time birds have existed on the earth and probably only determined the details of migrations as we see them today (Moreau 1951).

The northern and southern ancestral home theories appear diametrically opposed to each other but Dorst (1963) concludes they are perfectly compatible. Since the phenomena probably occurred simultaneously, northern migrants then originated from two stocks: the North Temperate Zone birds sought refuge to the south during the glacial periods and the tropical avifauna expanded their range during the interglacial periods. Dorst also stated this double origin is more prevalent in North America where the tropical element is most abundant. Birds representing this element include hummingbirds, tyrant flycatchers, orioles, tanagers, and blackbirds. At some latitudes, they nest in the same area as the shorebirds which are of arctic parental stock.

These theories assume migration is a genetic, inherited character, but we now know in some species it can be modified in the lifetime of one individual and the place some individuals return to nest or winter is not the ancestral home but a place to which they had been transported at an early stage in their development. Traditions that have lived for countless generations may die overnight if experienced individuals are lost or no longer active (Hochbaum 1955); migration patterns remain constant only as long as the factors influencing these patterns remain constant. But the landscape and the interacting ecological stresses are forever changing, and we would expect the adaptive behavior of birds to respond with them. One of these responses to an expanding habitat is colonization of new territory and expansion of a species' range with accompanying development of a migratory habit. The search for favorable conditions under which to breed in summer and to feed in winter, as influenced by competition for space, has been the principal factor underlying the extension of ranges, usually by young, nonconditioned individuals. This is exemplified by the northward extension in historic times of a number of species. Many of these range extensions have closely followed man's settlement of the area and the subsequent changes in habitat that man has made.

From the previous descriptions of migration patterns and routes, it will be observed that the general trend of migration in most northern populations of North American birds is northwest and southeast. Eastern species tend to extend their ranges by pushing westward, particularly in the North. For example, in the Stikine River Valley of northern British Columbia and southwestern Alaska the common nighthawk, chipping sparrow, rusty blackbird, yellow warbler, American redstart, and others have established breeding stations at points 20 to 100 miles from the Pacific Ocean. The northern race of the American robin, common flickers, dark-eyed juncos, blackpoll warblers, yellow-rumped warblers, and ovenbirds, all common eastern species, also are established as breeding birds in western Alaska. The ovenbird has even been detected on the lower Yukon River, and the sandhill crane and gray-cheeked thrush have moved across Bering Strait into Siberia. These birds continue to migrate through the eastern part of the continent. Instead of taking the shortest route south, they retrace the direction of their westward expansion and move southward along the same avenues as their more eastern relatives.

The red-eyed vireo is essentially an inhabitant of states east of the Great Plains, but an arm of its breeding range extends northwest to the Pacific coast in British Columbia (Fig. 30). It seems evident this is a range extension that has taken place comparatively recently by a westward movement via deciduous woodland corridors, and the invaders retrace in spring and fall the general route by which they originally entered the country.

In the case of the bobolink, a new extension of the breeding range and a subsequent change in the migration of the species has taken place since settlement by European man (Fig. 19). Because the bobolink is a bird of damp meadows, it was originally cut off from the Western States by the intervening arid regions, but with the advent of irrigation and the bringing of large areas under cultivation, small colonies of nesting bobolinks appeared at various western points. Now the species is established as a regular breeder in the great mountain parks and irrigated valleys of Colorado and elsewhere almost to the Pacific coast. These western pioneers must fly long distances east and west to reach the western edge of the route followed by the bulk of the bobolinks that breed in the northern United States and southern Canada.

During the past few decades, various populations of Canada geese have altered their migration patterns as a result of transplanting brood stock, development of refuges or changing agricultural practices. These routes will continue to change in the coming years as long as these factors are in a state of flux. It has been shown that man can establish breeding colonies of Canada geese with young birds almost anywhere.

Europe also has several good examples of changes in migration routes through range extension. One of the best examples is the serin. During the past century, this European finch has spread its breeding range from around the Mediterranean Sea to include the entire continent. While the Mediterranean populations remain sedentary, the more northern breeding birds are migratory. Most likely, those birds that did not migrate from the North were eliminated by severe weather. Similarly, the wheatear, yellow wagtail, and Arctic warbler have extended their breeding ranges eastward across the Bering Sea into Alaska, but the wheatear, for instance, migrates all the way back across Asia to Africa where it winters with other wheatears coming from Europe, Iceland, and Greenland.

As bird populations become more and more migratory, we might expect their flight capabilities to be enhanced accordingly. These changes in morphology are readily seen in wing shape. Several groups of birds have closely related species or populations some of which are migratory and others sedentary. The sedentary species or populations have more rounded wings because of the relative length of the wing quills. On the other hand, populations that migrate great distances, such as albatrosses, falcons, swifts, various shorebirds, and terns, have more pointed wings. Kipp(1942, 1958) demonstrated this using orioles. The sedentary black-headed oriole of India has a well-rounded wing whereas the closely related black-naped oriole is migratory between India and Siberia and has primaries that are much more pointed and well developed.

Thus it seems the origin and evolution of migration have roots in the present that are deep in the past. The important thing to consider in the evolution of a migratory trait is whether a population can adapt to new conditions by genetic modification of its physiology and habits. The migratory habit has evolved in those populations in which, on the average, more individuals survive by moving to a different area part of the year than if they remained in the same area all year.

=WHERE WE STAND=

The migration of birds had its beginning in times so remote its origins have been largely obscured and can be interpreted now only in terms of present conditions. The causes underlying migration are exceedingly complex. The mystery that formerly cloaked the periodic travels of birds, however, has been largely dispelled through the fairly complete information now available concerning the extent and times of seasonal journeys of most species. Many gaps still remain in our knowledge of the subject, but present knowledge is being placed on record, and the answers to many uncertainties that continue to make bird migration one of the most fascinating subjects in the science of ornithology must be left for future studies. In some areas we are on the threshold of discovery. More and more sophisticated approaches including radar, radio telemetry, computer processing of banding data, and physiological and behavior studies are being developed.

With the widespread use of these new techniques, we are beginning to realize the benefits, aside from aesthetic reasons, for studying migration. Radar alone has aided tremendously in documenting flock size, heights, and speeds of migration as well as the descriptions and locations of patterns and routes of specific migrants in relation to aircraft flight lanes. Recent studies have indicated local, nonmigratory populations of various blackbirds cause nearly all of the rice damage in southern States and the "hordes from the North" contribute very little to the losses. In addition, the transport of arborviruses from one continent to another via these long distance migrants is being investigated. People have started to uncover the secrets of migration and utilize this knowledge for the betterment of our society.

Each kind of bird seems to have its own reaction to the environment, so that the character of movement differs widely in the various species, and seldom do any two present the same picture. In fact, bird migration has been described as a phase of geographic distribution wherein there is a more or less regular seasonal shifting of the avian population caused by the same factors that determine the ranges of the sedentary species. If this view is correct, then it must be recognized that the far-reaching works of man in altering the natural condition of the Earth's surface can so change the environment necessary for the well-being of the birds as to bring about changes in their yearly travels. The nature and extent of the changes wrought by man on the North American Continent are readily apparent. Extensive forests have been burned or cut away, rolling prairies turned over with the plow, and wetlands drained or filled. Their places have been taken by a variety of human activities. These great changes are exerting pressure on native bird populations, and various species may be either benefited or adversely affected.

The Federal Government has recognized its responsibility to migratory birds under these changing conditions. Enabling acts allow for carrying out migratory bird treaty obligations in cooperation with other countries, and now most species have legal protection under regulations administered by the U.S. Fish and Wildlife Service. The effectiveness of conservation laws, however, is increased in the same measure that the people of the country become acquainted with the migratory bird resource and interest themselves personally in the well-being of the various species. Long before European man came to America, the birds had established their seasonal patterns of migration throughout the Western Hemisphere. The economic, scientific, and esthetic values of these migratory species dictate they be permitted to continue their long-accustomed and to some extent still-mysterious habits of migration.

=BIBLIOGRAPHY=

Able, K. P.

1970. A radar study of the altitude of nocturnal passerine
migration. Bird-Banding 41(4): 282-290.

Aldrich, J. W.

1949. Migration of some North American waterfowl. U.S. Fish and
Wildl. Serv., Spec. Sci. Rep. Wildl. 1. 49 p.

Aldrich, J. W.

1952. The source of migrant mourning doves in southern Florida. J.
Wildl. Manage. 16:447-456.

Aldrich, J. W., A. J. Duvall and A. D. Geis.

1958. Racial determination of origin of mourning doves in hunters'
bags. J. Wildl. Manage. 22: 71-75.

Alexander, J. R., and W. T. Keeton.

1972. The effect of directional training on initial orientation in
pigeons. Auk 89: 280-298.

Allard, H. A.

1928. Bird migration from the point of light and length of day
changes. Am. Nat. 62: 385-408.

American Ornithologists' Union.

1957. The Check-list of North American birds. 5th edition. American
Ornithologists' Union. 691 p.

Anderson, K. S., E. J. Randall, A. J. Main and R. J. Tonn.

1967. Recoveries of birds banded by encephalitis field stations,
1957-1965. Bird-Banding 38(2): 135-138.

Annan, O.

1962. Sequence of migration by sex, age, and species of thrushes
of the genus _Hylochichla_ through Chicago. Bird-Banding 33(3):
130-137.

Anonymous.

1972. Population ecology of migratory birds. A symposium. Wildl.
Res. Rep. 2. U.S. Fish and Wildl. Serv. 278 p.

Austin, O. L., Jr.

1928. Migration routes of the Arctic Tern (_Sterna paradisaea_
Brunnich). Northeast Bird Banding Assoc. 4(4): 121-125.

1929. Some Labrador banding records. Northeast Bird Banding Assoc.
5(1): 35-36.

Bagg, A. M.

1967. Factors affecting the occurrence of the Eurasian Lapwing in
eastern North America. Living Bird 6: 87-121.

Bagg, A. M., W. W. H. Gunn, D. S. Miller, J. T. Nichols, W. Smith and F. P. Wolfarth.

1950. Barometric pressure patterns and spring bird migration.
Wilson Bull. 62: 5-19.

Baird, J., C. S. Robbins, A. M. Bagg and J. V. Dennis.

1958. "Operation Recovery" the Atlantic coastal netting project.
Bird-Banding 29(3): 137-168.

Baird, J., A. M. Bagg, I. C. J. Nisbet and C. S. Robbins.

1959. Operation Recovery--report of mist-netting along the Atlantic
coast in 1958. Bird-Banding 30: 143-171.

Ball, S. C.

1952. Fall bird migration of the Gaspe Peninsula. Peabody Mus. Nat.
Hist. Yale Univ. Bull. 7. 211 p.

Behle, W. H.

1958. The bird life of Great Salt Lake. Univ. of Utah Press, Salt
Lake City. 203 p.

Bellrose, F. C.

1967. Radar in orientation research. Proc. XIX Int. Ornithol.
Congr.: 281-309.

Bellrose, F. C.

1968. Waterfowl migration corridors east of the Rocky Mountains
in the United States. Biol. Notes 61, Ill. Nat. Hist. Surv.,
Urbana, Ill 24 p.

1971. The distribution of nocturnal migration in the air space. Auk
88(2): 397-424.

1972a. Possible steps in the evolutionary development of bird
navigation p. 223-257. In: Caller, S. R. et al. ed. Animal
orientation and navigation symp. N.A.S.A. Wash., D.C. 606 p.

1972b. Mallard migration corridors as revealed by population
distribution, banding, and radar. In: Population ecology of
migratory birds: A Symp. Wildl. Res. Rep. 2. U.S. Fish and
Wildl. Serv. p. 1-26.

Bellrose, F. C. and R. R. Graber.

1963. A radar study of the flight directions of nocturnal migrants.
Proc. XIII Int. Ornithol. Congr: 362-389.

Bellrose, F. C. and J. G. Sieh.

1960. Massed waterfowl flights in the Mississippi flyway 1956 and
1957. Wilson Bull. 72: 29-59.

Bennett. H. R.

1952. Fall migration of birds at Chicago. Wilson Bull. 64: 197-220.

Bergman, G. and K. O. Donner.

1964. An analysis of spring migration of the Common Scoter and
Longtailed Duck in southern Finland. Acta Zool. Fenn. 105: 1-59.

Bergtold, W. H.

1926. Avian gonads and migration. Condor 28: 114-120.

Bissonette, T. H.

1936. Normal progressive changes in the ovary of the starling
(_Sturnus vulgaris_) from December to April. Auk 53: 31-50.

1939. Sexual photoperiodicity in the blue jay (_Cyanocitta
cristata_). Wilson Bull. 51: 227-232.

Bogert. C.

1937. The distribution and the migration of the Long-tailed Cuckoo
(_Urodynamis taitensis_ Sparrman). Am. Mus. Novit. 933. pp 1-12.

Bourne, W. R. P.

1956. Migrations of the sooty shearwater. Sea Swallow 9: 23-25.

Bray, O. E. and G. W. Corner.

1972. A tail clip for attaching transmitters to birds. J. Wildl.
Manage. 36(2): 640-642.

Broley. C. L.

1947. Migration and nesting of Florida bald eagles. Wilson Bull.
59: 3-20.

Bruderer, B. and P. Steidinger.

1972. Methods of quantitative and qualitative analysis of bird
migration with a tracking radar, p. 151-167. In: Caller, S.
R., et al ed. Animal orientation and navigation symp. N.A.S.A.
Wash., D.C. 606 p.

Clarke, W. E.

1912. Studies in bird migration. 2 vol. London.

Coffey, B. B., Jr.

1944. Winter home of chimney swifts discovered in northeastern
Peru. Migrant 15(3): 37-38.

Cooch, G.

1955. Observations on the autumn migration of blue geese. Wilson
Bull. 67(3): 171-174.

Cooke, M. T.

1937. Flight speed of birds. U.S. Dept. Agr. Cir. 428. 13 p.

1945. Transoceanic recoveries of banded birds. Bird-Banding 16(4):
123-129.

Cooke, W. W.

1888. Report of bird migration in the Mississippi Valley in the
years 1884 and 1885. U.S. Dept. Agr. Div. Econ. Ornithol. Bull.
2. 313 p.

1904a. Distribution and migration of North American warblers. U.S.
Dept. Agr. Div. Biol. Surv. Bull. 18. 142 p.

1904b. The effect of altitude on bird migration. Auk 21: 338-341.

Cooke, W. W.

1905a. Routes of bird migration. Auk 22: 1-11.

1905b. The winter ranges of the warblers (Mniotiltidae). Auk 22:
296-299.

1906. Distribution and migration of North American ducks, geese,
and swans. U.S. Dept. Agr. Bur. Biol. Surv. Bull. 26. 90 p.

1908. Averaging migration dates. Auk 25: 485-486.

1910. Distribution and migration of North American shore birds.
U.S. Dept. Agr. Bur. Biol. Surv. Bull. 35. 100 p.

1913a. Distribution and migration of North American herons and
their allies. U.S. Dept. Agr. Bur. Biol. Surv. Bull. 45. 70 p.

1913b. The relation of bird migration to the weather. Auk 30:
205-221.

1914. Distribution and migration of North American rails and their
allies. U.S. Dept. Agr. Bull. 128. 50 p.

1915a. Bird migration. U.S. Dept. Agr. Bull. 185. 48 p.

1915b. Bird migration in the Mackenzie Valley. Auk 32: 442-459.

1915c. Distribution and migration of North American gulls and their
allies. U.S. Dept. Agr. Bull. 292. 70 p.

1915b. The Yellow-billed loon: a problem in migration. Condor 17:
213-214.

Cortopassi, A. J. and L. R. Mewaldt.

1965. The circumannual distribution of white-crowned sparrows.
Bird-Banding 36(3): 141-169.

Coues, E.

1878. Birds of the Colorado Valley: a repository of scientific and
popular information concerning North American ornithology. U.S.
Dept. Int. Misc. Pub. 11. 807 p.

Curtis, S. G.

1969. Spring migration and weather at Madison, Wisconsin. Wilson
Bull. 81(3): 235-245.

Delacour, J.

1947. Birds of Malaysia. Macmillan Co. N.Y. 382 p.

1963. The waterfowl of the world, 4 vols. Country Life Ltd. London.

DeLury, R. E.

1938. Sunspot influences. J. R. Astron. Soc. of Can. pt. 1, March
1938, pt. 2, April 1938. 50 p.

Dennis, J. V.

1967. Fall departure of the Yellow-breasted Chat (_Icteria virens_)
in eastern North America. Bird-banding 38 (2): 130-135.

De Schauensee, R. M.

1970. A guide to the birds of South America. Livingston Pub. Co.
Wynnewood, Penn. 470 p.

Diem, K. L. and D. D. Condon.

1967. Banding studies of water birds on the Molly Islands,
Yellowstone Lake, Wyoming. Yellowstone Lib. and Mus. Assoc.,
Yellowstone Nat. Park. 41 p.

Dixon, J.

1916. Migration of the Yellow-billed Loon. Auk 33 (4): 370-376.

Dixon, K. L. and J. D. Gilbert.

1964. Altitudinal migration in the Mountain Chickadee. Condor 66:
61-64.

Dorst, J.

1963. The migration of birds. Houghton Mifflin Co. (Am. ed),
Boston. 476 p.

Drury, W. H. Jr.

1960. Radar and bird migration a second glance. Mass. Audubon
44(4): 173-178.

Drury, W. H. Jr., I. C. T. Nisbet and R. E. Richardson.

1961. The migration of angels. Nat. Hist. 70(8): 10-17.

Eastwood, E.

1967. Radar ornithology. Methuen, London. 278 p.

Eastwood, E. and G. C. Rider.

1965. Some radar measurements of the altitude of bird flight. Br.
Birds 58: 393-426.

Eaton, R. J.

1933. The migratory movements of certain colonies of Herring Gulls
(_Larus argentatus smithsonianus_ Coues) in eastern North
America. Part I. Bird-Banding 4(4): 165-176.

Eaton, R. J.

1934. The migratory movements of certain colonies of Herring Gulls
in eastern North America. Part II. Bird-Banding 5(1): 1-19.

1934. The migratory movements of certain colonies of Herring Gulls
in eastern North America. Part III. Bird-Banding 5(2): 70-84.

Emlen, S. T.

1967. Migratory orientation in the Indigo Bunting (_Passerina
cyanea_). Part II: Mechanism of celestial orientation. Auk 84:
463-489.

1969. Bird migration: influence of physiological state upon
celestial orientation. Science (Wash., D.C.) 165 (3894): 716-718.

1970. The influence of magnetic information on the orientation
of the Indigo Bunting (Passerina cyanea). Anim. Behav. 18(2):
215-224.

Farner, D. S.

1945. The return of Robins to their birthplaces. Bird-Banding
16(3): 81-99.

1950. The annual stimulus for migration. Condor 52(3): 104-122.

1955. The annual stimulus for migration: experimental and
physiologic aspects. In: Recent studies in avian biology. Univ.
Ill. (Urbana) Bull: 198-237.

1960. Metabolic adaptations in migration. Proc. XII Int. Ornithol.
Cong.: 197-208.

Farner, D. S. and L. R. Mewaldt.

1953. The relative roles of diurnal periods of activity and
diurnal photoperiods in gonadal activation in male _Zonotrichia
leucophrys gambelii_. Experimentia 9: 219-221.

Fisher, H. I. and J. R. Fisher.

1972. The oceanic distribution of the Laysan Albatross (_Diomedea
immutabilis_). Wilson Bull 84: 7-27.

Fisher, J. and R. M. Lockley.

1954. Sea-birds. Houghton Mifflin, Boston. XVI + 320 p.

Furlong, W. R.

1933. Land-birds in a gale at sea. Bird Lore 35(5): 263-265.

Gatke, H.

1895. Heligoland as an ornithological observatory: the results of
fifty years' experience (trans, from German by R. Rosenstock).
David Douglas Pub., Edinburgh. 599 p.

Gauthreaux, S. A. Jr.

1970. Weather radar quantification of bird migration. Bioscience
20(1): 17-20.

1971. A radar and direct visual study of passerine spring migration
in southern Louisiana. Auk 88: 343-365.

1972a. Flight directions of passerine migrants in daylight and
darkness: a radar and direct visual study p. 129-137. Galler,
S. R., et al. ed. In: Animal orientation and navigation symp.
N.A.S.A. Wash., D.C. 606 p.

1972b. Behavioral responses of migrating birds to daylight and
darkness: a radar and direct visual study. Wilson Bull. 84:
136-148.

Geroudet, P.

1954. Des oiseaux migrateurs trouvés sur la glacier de Khumbu dans
l'Himalaya. Nos Oiseaux 22: 254.

Godfrey, W. E.

1966. The birds of Canada. Natl. Mus. Can. Bull. 203, Biol Series
No. 73. 428 p.

Gordon, D. A.

1948 Some considerations of bird migration: continental drift and
bird migration. Science (Wash., D.C.) 108: 705-711.

Graber, R. R.

1965. Night flight with a thrush. Audubon 67: 368-374.

1968. Nocturnal migration in Illinois different points of view.
Wilson Bull. 80(1): 36-71.

Graber, R. R. and W. W. Cochrane.

1959. An audio technique for the study of nocturnal migration of
birds. Wilson Bull. 71: 220-236.

Griffin, Dr. R.

1940. Homing experiments with Leach's Petrels. Auk 57(1): 61-74.

1943. Homing experiments with Herring Gulls and Common Terns.
Bird-Banding 14(1 and 2): 7-33.

Griffin, D. R.

1958. Listening in the dark. Yale Univ. Press, New Haven. 413 p.

1964. Bird migration. Nat. Hist. Press. Garden City, N.Y. 180 p.

Griffin, D. R. and R. J. Hock.

1948. Experiments on bird navigation. Science (Wash., D.C.)
107(2779): 347-349.

1949. Airplane observations of homing birds. Ecology 30: 176-198.

Grinnell, J.

1931. Some angles in the problem of bird migration. Auk 48: 22-32.

Gross, A. O.

1927. The Snowy Owl migration of 1926-27. Auk 44: 479-493.

1947. Cyclic invasions of the Snowy Owl and the migration of
1945-46. Auk 64(4): 584-601.

Gwynn, A. M.

1968. The migration of the Arctic Tern. Aust. Bird Bander 6(4):
71-75.

Haartman, L. von.

1968. The evolution of resident vs. migratory habit in birds: some
considerations. Ornis Fenn. 45(1): 1-7.

Hagar, J. A.

1966. Nesting of the Hudsonian Godwit at Churchill, Manitoba.
Living Bird 5: 5-43.

Hamilton, W. J. III.

1962a. Bobolink migratory pathways and their experimental analysis
under night skies. Auk 79(2): 208-233.

1962b. Celestial orientation in juvenile waterfowl. Condor 64(1):
19-23.

Harrisson, T. H.

1931. On the normal flight speeds of birds. Br. Birds 25: 86-96.

Hassler, S. S., R. R. Graber and F. C. Bellrose.

1963. Fall migration and weather: a radar study. Wilson Bull. 75:
56-77.

Haugh, J. R. and T. J. Cade.

1966. The spring hawk migration around the southeastern shore of
Lake Ontario. Wilson Bull. 78(1): 88-110.

Hebrard, J. J.

1971. The nightly initiation of passerine migration in spring: a
direct visual study. Ibis 113(1): 8-18.

Hochbaum, H. A.

1955. Travels and traditions of waterfowl. Univ. of Minn. Press,
Minneapolis. 301 p.

Hofslund, P. B.

1965. Hawks above Duluth. In: The bird watcher's America, ed. O. S.
Pettingill, Jr. McGraw-Hill Book Co., N. Y.

1966. Hawk migration over the western tip of Lake Superior. Wilson
Bull. 78: 79-87.

Hussell, D. J. T., T. Davis and R. D. Montgomerie.

1967. Differential fall migration of adult and immature Least
Flycatchers. Bird-Banding 38(1): 61-66.

Jaeger, E. C.

1948. Does the Poor-will "hibernate"? Condor 50: 45.

1949. Further observations on the hibernation of the Poor-will.
Condor 51: 105-109.

Johnson, N. K.

1963. Comparative molt cycles in the Tyrannid genus _Empidonax_.
Proc. XIII Int. Ornithol. Congr.: 870-883.

1973. Spring migration of the Western Flycatcher with notes on
seasonal changes in sex and age ratios. Bird-Banding 44(3):
205-220.

Keeton, W. T.

1969. Orientation by pigeons: is the sun necessary? Science (Wash.,
D. C.) 165(3896): 922-928.

Kenyon, K. W. and D. W. Rice.

1958. Homing of Laysan Albatrosses. Condor 60: 3-6.

King, J. R.

1963. Annual migratory-fat deposition in the White-crowned Sparrow.
Proc. XIII Int. Ornithol. Congr.: 940-949.

King, J. R., S. Barker and D. S. Farner.

1963. A comparison of energy reserves during the autumnal
and vernal migratory periods in the White-crowned Sparrow
(_Zonotrichia leucophrys gambelii_). Ecol. 44(3): 513-521.

King, J. R. and D. S. Farner.

1963. The relationship of fat deposition to Zugunruhe. Condor
65(3): 200-223.

Kipp, F. A.

1942. Ueber Flugelban and Wanderzug der Vogel. Biol. Zbl. 62:
289-299.

1958. Zur Geschichte des Vogelzuges auf der Grundlage der
Flugelanpassungen. Vogelwarte 19: 233-242.

Kramer, G.

1952. Experiments on bird orientation. Ibis 94: 265-285.

1957. Experiments on bird orientation and their interpretation.
Ibis 99: 196-227.

1959. Recent experiments on bird orientation. Ibis 101: 399-416.

1961. Long distance orientation. In: Marshall, A. J. Biology and
comparative physiology of birds. 2 Vol. Academic Press, N.Y. and
London.

Kuroda, N.

1957. A brief note on the pelagic migration of the Tubinares. Misc.
Rep. of the Yamashina Inst. for Ornithol. and Zool. 11: 10-23.

Lack, D.

1959. Migrations across the sea. Ibis 101(3-4): 374-399.

1960a. The influence of weather on passerine migration. Auk 77:
171-209.

Lack, D.

1960b. The height of bird migration. Br. Birds 53: 5-10.

1962. Radar evidence on migratory orientation. Br. Birds 55(4):
139-157.

1963a. Migration across the southern North Sea studied by radar.