Yellow Wagtail 36.Motacilla flava Transhumance in the Sahel has special importance for Yellow Wagtails. Thousands of Wagtail fl ocks attend the cattle, sheep and goats as they sweep across plains, savanna and desert, profi ting from seasonal variations in food supply. The region covered by the 110 million herbivores in the western Sahel lies roughly between the zones that receive less than 100 mm of rainfall (insuffi cient for grass) and more than 1000 mm of rainfall (where tsetse fl ies reign), and within it, fl oodplains provide temporary food bonanzas when grasses put on growth spurts once the water has receded. From December to April, depending on the height of the fl ood, a paradise for fi sherman is transformed into a pastoralist’s idyll. The arrival of large herds in the defl ooded areas heralds an infl ux of Yellow Wagtails, whose thin high-pitched calls are easily audible above the bellows, grunts and trampling of the cattle. Nowhere particularly abundant during daytime, Wagtails leap to prominence just before dusk, when the magnitude of their numbers be- comes obvious, as a continuous stream starts heading for the roost. For as far as the eye can see along the column, it’s Wagtails galore. Counting is a near-impossibility, because the bulk passes when it is almost dark. The scale of roost migration, however, does give a fair impression of the populations hosted by huge Eurasian hinterland where these wagtails breed, and to which they are preparing to return, despite often harsh conditions en route. 4418 Livvinng onn thee edge Breeding range which occupy central and northern parts of the country from Vom to Nguru and Lake Chad (Fry et al. 1970, Wood 1975 & 1992, Bell 2006). Yellow Wagtails breed across Europe as far north as the 10°C iso- The evidence from ringing also indicates a latitudinal variation in therm, covering all climatic zones between Arctic tundra and Medi- sex ratio, with males on average wintering further north than fe- terranean. Densities are highest in northern and eastern Europe. males (Wood 1992). The latest estimate for Europe amounted to 8-14 million breeding pairs in the late 1990s, mostly in eastern Europe, Belarus, Russia and Turkey (BirdLife International 2004a). Several subspecies are Distribution in Africa recognised, of which the Egyptian M.f. pygmaea is an endemic resi- dent and the Moroccan population of M.f. iberiae partly so (Théven- In sub-Saharan Africa Yellow Wagtails are among the most ubiqui- ot et al. 2003). In Europe, all populations are migratory and winter tous of insectivorous Palearctic migrants. The locally breeding throughout Africa south of the Sahara (i.e. flavissima, flava, thunber- Plain-backed Pipit Anthus leucophrys is one of the few insectivorous gi, cinereocapilla, feldegg, beema and lutea). The easternmost recov- residents that uses the same niche, but it is greatly outnumbered by ery of a Yellow Wagtail ringed in Africa came from the Ob in western the millions of Yellow Wagtails. There are few African habitats to- Siberia at about 77°E (Zink 1975); this bird must have been M.f. tally devoid of Yellow Wagtails, mostly crowded human settlements thunbergi, of which a large part of the population winters in Africa or woodland without glades, but densities vary considerably. (otherwise on the Indian subcontinent). Based on densities found during plot sampling in various habi- tats in West Africa (Chapter 11), we found Yellow Wagtails to be the commonest winter visitors in rice fields in Senegambia, Guinea- Migration Bissau and Guinea-Conakry. The average density in the winters of 2004/2005 and 2005/2006 was 2.37 birds/ha, which results in an es- The distribution and abundance of Yellow Wagtails in Africa south timated number of 268 000 birds wintering in the 1120 km2 of rice of the Sahara is complex, with racial variations in distribution, lati- tudinal variations in sex ratio and seasonally induced fluctuations in numbers (Wood 1992, Bell 1996, 2007a, 2007b). The available evi- dence converges on a west to east gradient of races wintering in Af- rica similar to those that comprise the Eurasian breeding distribu- tion (Zink 1975; Fig. 243). Western European Yellow Wagtails of the race M.f. flavissima winter mainly in Senegambia through Guinea- Bissau and Guinea to Sierra Leone. The races flava and thunbergi, originating from breeding areas between 10° and 30°E, winter largely in the West African sector between the Inner Niger Delta and Lake Chad. Birds in the eastern half of the Sahel and in eastern Af- rica constitute a mixture of northern and eastern European races like thunbergi, flava, feldegg and lutea; birds ringed in Kenya were recovered mainly in Europe east of 30°E in Russia (Zink 1975). Rus- sian and Kazakh Yellow Wagtails breeding east of the Caspian Sea winter partly in the Indian subcontinent (McClure 1974), but M.f. lutea is also a widespread winter visitor to East Africa (Keith et al. 1992). Within the Sahel zone, the British birds winter, on average, 1000 km further to the west than Swedish birds, and Finnish birds 1350 km further to the east of Swedish birds (Fig. 243). This is just a crude division, and in reality there is much overlap between the win- tering areas throughout the Sahel, and even in smaller geographic components like Nigeria (Wood 1975). On top of a west-east gradient in distribution within the sub-Sa- hara depending on breeding origin, northernmost Yellow Wagtails are known to undertake leap-frog migration over more southerly breeding birds to winter further south (Wood 1975, 1992, Bell 1996). Fig. 243 European origins of 354 Yellow Wagtails recovered between 4° In Nigeria, for example, thunbergi (from Scandinavia) winter south and 37°N. From: euring. To avoid cluttering the figure, lines are not of cinereocapilla (Italy), feldegg (Balkan) and flava (central Europe), shown for recoveries in southern Spain and NW Africa. Yeelloww Wagttaiil MMotaccilla flava 419.