An analysis of the spring migration of the Common Scoter and by Goran Bergman

By Goran Bergman


I. creation 3
II. equipment 7
1. fabric and means of recording 7
2. movie research 7
three. The meteorological info 9
III. The identity of the migrants 10
IV. the rate and course of migration thirteen
1. the rate of flight and its dependence on quite a few exterior and internal
factors 13
2. The path of migration and the criteria affecting it 21
three. The effect of topographical elements at the course 36
V. The influence of meteorological components at the depth of migration 44
1. power and course of the wind 45
2. Cloudiness 47
three. Visibility 49
four. Temperature 50
VI. The geographical distribution of the migration 50
Summary 54
References fifty seven

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Additional resources for An analysis of the spring migration of the Common Scoter and the Long-tailed Duck in southern Finland

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0 . __ iI I I I I I I , ... / I I FIG. 1 4. General course of the migration in daylight with high or medium visibilitv. Note general absence of migrants over land, except a few flocks in the lake region (�e p. 42 and 52). 3. The influence of top ographical factors on the direction The analysis described in the preceding paragraphs has deliberately been carried out with material from areas that show only little of the very clear effects exerted upon the direction of migration by local topographical factors.

36) . With S and E winds it is clear that the birds tend to drift more to the north and this will accumulate them along the coast, which they "rill avoid to cross in daylight. Under such conditions an observer in the archipelago (BERGMAN's observations were carried out at Kopploma 12 km WSW of Helsingfors) will record the highest intensities of migration, although the effect is only a local one not directly depending on the general intensity of migration. A similar tendency to migrate in following winds is evident from HARPER's (1957) first report and is demonstrated by LACK ( 1 962 b, 1963 a, b) in his analysis of the migration across the southern North Sea.

With a full overcast practic­ ally no migration can be observed. (Fig. ) 1 4 . Changes in horizontal visibility appear to affect the intensity of migration very little or not at all. (Fig. 15. ) The actual routes taken by the migrating flocks as well as the geo­ graphical distribution of the migrants are strongly affected by local topo­ graphical conditions and by the prevailing weather (\\-ind, doudiness, visibility) . Different combinations of these factors give rise to various specific routes of migration.

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