Lengthening Of Migration Routes

In species that have expanded their breeding areas to higher latitudes yet have retained the same wintering areas, some extension of migration routes is inevitable. Eurasian examples include: (1) Black-winged Stilt Himantopus himantopus, which is expanding its breeding range northward (France, Ukraine, Russia) but still winters south of 40°N latitude; (2) European Bee-eater Merops apiaster, which has expanded northwards in almost all central European countries, yet still winters entirely in Africa south of the Sahara; (3) Citrine Wagtail Motacilla citreola, which is expanding its breeding range from Asia westward into Europe, but still winters in India and Southeast Asia (Fiedler 2003). The intra-European routes have increased by up to 1000 km. These examples represent the sort of changes that must have occurred in many species after each glaciation, when ice receded, and plants and animals spread from lower to higher latitudes (Chapter 22).

In the Red-breasted Goose Branta ruficollis, most individuals now winter in Romania-Bulgaria, some 300-600 km further from their breeding areas than in the 1950s, as former wintering sites in Azerbaijan have been altered by land use changes (Sutherland & Crockford 1993). In even earlier times, the species was found in winter yet further from its breeding areas, being depicted in the art of ancient Egypt (Houlihan 1986). So over recorded history, this species has both shortened and lengthened its migration routes. Such changes in the length of migrations could initially involve only facultative responses to local conditions but, as migrations lengthen over time, some genetic change seems likely, as they would require changes to the regulatory mechanisms.

In some other species, greater proportions of ring recoveries are now being obtained from the distant parts of migration routes than formerly, but it is hard to tell whether this is due to altered migration behaviour, or to changed recovery chances along the routes (Fiedler et al. 2004). In particular, over recent decades hunting has declined much more in the northern and mid-latitudes of Europe than further south. This could affect the migratory behaviour of hunted species, or the distribution of their ring recoveries.

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