Nicolas Martinez, Simon Hohl, Valentin Moser, Dominic Eichhorn, Tobias Roth, Daniel Matti
(* = Kurzbeitrag)
Die Unterarten der Schafstelze Motacilla flava auf dem Frühjahrs- und Herbstzug in der Schweiz.
(von 1994 bis 2006 vergeben)
Durchzug, Frühjahrszug, Herbstzug, Beringungsstation, Museumssammlungen, Geschlechtsverhältnis, Alter, Unterart
Motacilla flava, Motacilla flava flavissima, Motacilla flava thunbergi, Motacilla flava feldegg, Motacilla flava cinereocapilla, Motacilla flava iberiae, Motacilla flava lutea
Schafstelze, Gelbkopfschafstelze, Thunbergschafstelze, Maskenschafstelze, Aschkopfschafstelze, Iberienschafstelze, Wolgaschafstelze
Nordwestschweiz, Aargau, Basel-Stadt, Basel-Landschaft, Solothurn, Elsass, Baden-Württemberg
The subspecies of the Western Yellow Wagtail Motacilla flava on spring and autumn migration in Switzerland. The Yellow Wagtail is a widespread breeding bird in Europe and Asia. Switzerland harbours a small population of around 500 breeding pairs of the subspecies flava and cinereocapilla. During migration in spring and autumn, the species is much more abundant. Beside the subspecies flava and cinereocapilla, also thunbergi and, more rarely, feldegg and birds with characters of the subspecies flavissima or lutea are recorded during migration.
In spring, subspecies identification of male Yellow Wagtails is often straightforward thanks to differences in the head markings. Nevertheless, there is little published information on subspecies composition and timing during spring migration. Even less is known from the autumn migration, mainly because subspecies identification is more difficult than in spring. However, under good observation conditions, males of several subspecies can be identified.
In order to find out which subspecies migrate through Northwestern Switzerland, we intensively searched for Yellow Wagtail flocks in spring and autumn between 2014 and 2020 and identified all males (416 in spring, 152 in autumn) to subspecies level where possible. In this article, the data are presented and compared with data from other sources, namely the database of the Swiss Ornithological Institute Sempach, the online platforms ornitho.ch, ornitho.at, ornitho.de and faune-alsace.org, the ringing station Col de Bretolet (Canton Valais), and the Swiss Rarity Committee (SRC). In addition, we consulted the records at the Museums of Natural History in Basel and Bern.
The subspecies flava is the most abundant subspecies in spring and autumn, followed in each case by thunbergi. The ratio of individuals of flava : thunbergi in spring lies between 2 : 1 and 3 : 1. However, as migration of thunbergi through Switzerland occurs on average later and more concentrated than in flava, the abundance ratios change during the spring migration: During peak passage of thunbergi in May, this subspecies is more abundant than flava. In autumn, thunbergi is clearly rarer than in spring; the ratio of individuals of flava : thunbergi is about 8 : 1. This difference may be explained by the fact that thunbergi migrates south mainly via the Balkan Peninsula and Greece in autumn, moves from East to Central and West Africa in winter and then returns to Europe via the western Mediterranean region and Italy.
Besides flava and thunbergi, the subspecies cinereocapilla also occurs in spring in all parts of Switzerland and it is probably about as common as thunbergi in the southern parts of the country. The subspecies feldegg and flavissima or lutea are clearly much rarer. Since most records of flavissima or lutea occur in the western part of the country, it is likely that most of these birds concern in fact flavissima.
There are no records of feldegg from autumn in Switzerland so far; given the south-eastern distribution of this subspecies, autumn records are anyway not to be expected. On the other hand, the occurrence of feldegg in spring fits well with the theory that birds may overshoot their actual breeding grounds on migration. The situation with flavissima is less clear; five previously accepted autumn records were rejected by the Swiss Rarity Committee in the course of a revision in 2017 because the range of variation in autumn plumage of the subspecies flava has not been sufficiently investigated. We found a total of four wagtails that would phenotypically fulfil the criteria for flavissima or lutea, but according to current knowledge, aberrant flava cannot be excluded with certainty. Switzerland lies only slightly east of the migration route of flavissima. The main reason for the complete lack of autumn records so far is therefore probably not so much the absence of flavissima as its lack of identifiability.
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