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| Dokumenttyp: | Aufsatz |
|---|---|
| Alle Autoren: | Milton W Weller |
| ISSN: | 0022-541X |
| OCLC-Nummer: | 479874163 |
| Sprachhinweis: | English |
| Anmerkungen: | Fig. 2. Distribution of breeding redheads. Indicated densities in the large enclosed area in the prairie region are based upon aerial population-index data of the U. S. Fish and Wildlife Service. Dotted lines indicate inexact boundaries; question marks indicate questionable records or areas where birds are suspected of breeding. Fig. 3. Distribution of wintering redheads, based on winter inventory data of the U. S. Fish and Wildlife Service. Circled areas are known wintering grounds. The dotted line indicates the most northerly records for areas having 100 or more wintering redheads during 1951-55. Fig. 4. Division of breeding range into regions and sub-regions, based on the dispersal of young to the three major wintering areas. The ratios are the numbers of recoveries from bandings at the indicated sites, taken at or en route to the West, Gulf, or East coasts. Fig. 5. Diagrammatic representation of the fall migration of the redhead. Width of the arrows indicates volume and is based on the percentage of birds using wintering areas. Fig. 6. Diagrammatic representation of the fall migration of the canvasback (after Stewart et al. 1958). Fig. 7. Direct (dots) and indirect (circles) recoveries of local redheads banded in Alberta. Fig. 8. Direct (dots) and indirect (circles) recoveries of local redheads banded in Saskatchewan. Fig. 9. Direct (dots) and indirect (circles) recoveries of local redheads banded in Manitoba. Fig. 10. Direct (dots) and indirect (circles) recoveries of local redheads banded in Minnesota. Fig. 11. Direct (dots) and indirect (circles) recoveries of local redheads banded in eastern North and South Dakota. Fig. 12. Direct (dots) and indirect (circles) recoveries of local redheads banded in western North Dakota. Fig. 13. Direct (dots) and indirect (circles) recoveries of local redheads banded in British Columbia. Fig. 14. Direct (dots) and indirect (circles) recoveries of local redheads banded in southeastern Oregon, northeastern California, and northwestern Nevada. Fig. 15. Direct recoveries of local redheads banded in the Bear River Marshes of Utah prior to 1941. Fig. 16. Direct recoveries of local redheads banded in the Bear River Marshes of Utah since 1940. Fig. 17. Indirect recoveries of local redheads banded in the Bear River Marshes of Utah. Fig. 18. Direct recoveries of adult redheads banded in southeastern Oregon (circles) and in southern Manitoba (dots). Fig. 19. Direct fall recoveries of adult redheads banded during the postbreeding season in southern Saskatchewan and Manitoba and in northern North Dakota. Fig. 20. Direct (fall following winter of banding) recoveries of adults banded in winter and spring at four banding stations (large dots) in New York. Numbers indicate areas where recoveries are concentrated. Fig. 21. Direct recoveries of adult redheads banded in winter and spring on the Detroit River, Michigan. Fig. 22. Direct recoveries of adult redheads banded in Nebraska during the spring migration. Fig. 23. Direct recoveries of adult redheads banded in Oklahoma during the spring migration. |
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Abstract:
An analysis of the distribution and migration of the redhead (Aythya americana) was based on aerial survey and band recovery data accumulated by the U. S. Fish and Wildlife Service. Additional data from states outside routine survey areas were obtained from state waterfowl biologists and from published data. The redhead is prevalent in the prairie pothole region, predominantly in the south and west. The redhead has recently expanded to marginal range in Alaska and in several southern states, probably as a result of the serious drought of 1958-61. Approximately 78 percent of all redheads winter on the east coast of Texas in the highly saline Laguna Madre. About 14 percent use the East Coast (Chesapeake Bay to Florida), less than 3 percent the West Coast. Small numbers of birds will winter wherever water remains free of ice. Fall migration starts in mid-September and reaches its peak in mid-October. Most birds are on the wintering areas in late November and December. Birds from the south and west parts of the prairie region move due south to Texas; birds reared in the east and north sections tend to move to the East Coast. Most birds from the Great Basin area move due south or southeastward to winter in Texas; relatively few migrate to the East Coast. Movements are sufficiently distinct that breeding populations can be distinguished on the basis of the proportion of birds moving to each of the three major wintering areas. Banding of adults on wintering areas indicated that a small percentage of birds shift from one wintering area to another. Late summer northward and eastward movements are common among juveniles and adults. The present distribution and migration pattern indicates that the redhead originated in western or southwestern North America. It is suggested that the redhead has only recently invaded the prairie pothole region, either because of loss of habitat in its area of origin or because of the expansion of a successful species.
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