GASTEREN H VAN (1988) Flight altitude and flock size of migrating Meadow Pipits Anthus pratensis. LIMOSA 61 (1): 13-18.

Meadow Pipit Anthus pratensis This paper discusses the variation during the day of flying height and flock size of migrating Meadow Pipits. The counts were collected between autumn 1982 and spring 1986 on two different sites (in spring and autumn) near Hoorn (NH). For the analysis of the variation of flying height and flock size during the day only counts from spring 1985 till spring 1986 were used. In side winds as well as in head winds Meadow Pipits fly rather low, but higher in spring than in autumn. In both seasons tailwinds provoke a distribution with many birds at higher flight levels, indicating that the field observer will miss many birds. For spring as well as for autumn there was during the morning a decreasing tendency in flying height. Flock sizes of migrating Meadow Pipits are changing continuously. When migration starts, the largest flocks are found in the highest height class. After a quick increase the migration intensity slowly decreases in the course ofthe morning (fig. I), which correlates with lower flight levels (fig. 2). At this time the largest flocks are found in the lowest height class (fig. 3). A possible explanation ofthis is given in fig. 5. The number ofrising birds coincides with the occurrence of the largest flocks in the highest height class and the other way around. At the time of the highest migration intensity (third hour in autumn) the numbers of ascending and descending birds are equal (fig. 3,4). This model seems to fit during autumn but less during spring. The spring situation is explained by the possibility that most groups fly at too high altitudes, preventing them to be detected by field observers

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