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Migration across the Southern North Sea studied by radar: 5. Movements in August, winter and spring, and conclusion
Lack, D. (1963). Migration across the Southern North Sea studied by radar: 5. Movements in August, winter and spring, and conclusion. Ibis 105(4): 461-492. hdl.handle.net/10.1111/j.1474-919X.1963.tb01587.x
In: Ibis. British Ornithologists' Union/Wiley: London. ISSN 0019-1019, more
Peer reviewed article  

Available in Author 
    VLIZ: Open Repository 253373 [ OMA ]

Keywords
    Aquatic birds; Migrations; ANE, North Sea, Southern Bight [Marine Regions]; Marine

Author  Top 
  • Lack, D.

Abstract
    Arrivals of gulls S.W. seem almost confined to late July.In August, the main movements are W. by day and night of Lapwings and S.S.E. by night of warblers. Sand Martins migrated at dawn directly from a large roost at 34 m.p.h.In midwinter, migration occurred in at least one direction almost every morning and night. “Hard-weather movements” west or south are initiated primarily by easterly or northerly winds respectively, and not by cold. The corresponding return movements, which sometimes follow immediately, arc initiated primarily by westerly or southerly winds respectively, but warmth has an influence in February. In midwinter, various species are evidently ready to travel in either the autumn or the spring direction, and wind-direction is the paramount factor determining which occurs.The big eastward departures in March and April occur mainly with westerly winds and in warm weather, both factors being important, but proportionately more departures occur against strong head or cross-winds than in autumn. The general weather situation has no direct influence.Starlings migrated directly from their roosts on a few mornings each spring, normally at sunrise but on one occasion some did so much earlier.In late April and May the chief movements are N.N.W. arrivals and onward passages of British summer visitors, N.E. departures of shore-birds, and N.N.E. departures of small passerines, presumably en route between Iberia and Norway. These movements occur mainly with southerly winds, but sometimes against the wind.“Reversed movements” W. or S.S.E. are much more frequent in spring than has previously been supposed. They occur exclusively with easterly or northerly winds respectively (like the midwinter movements).The frequency of each migratory movement throughout the year is summarized in Table 6.The main findings of the 5-year study are reviewed under four heads in the Conclusion.

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