Altitudinal migration
SPRING migration is fully underway in the northern hemisphere by April, with millions of birds heading north to their breeding areas. While most birds fly thousands of miles, there are some which travel much shorter distances. These are altitudinal migrants which simply move between higher and lower elevations.
The reasons for altitudinal migration are probably many, with the prime mover being that habitat at higher altitudes becomes less hospitable in winter, with food supplies dwindling and weather conditions getting worse. Unlike other forms of migration, altitudinal migration can be in any direction, it just has to take birds to lower altitudes and back again.
It occurs in mountainous regions worldwide, on every continent except Antarctica. A look at the feeding regimes of the bird species involved shows that more than half in the Palearctic feed on invertebrates, while in the Neotropics fruit-eaters and nectar-feeders predominate.
A recent study of the world’s birds found that 1,238 species from 130 families undertake some form of altitudinal migration, and of these 830 species are passerines from 77 families. However, very few studies have taken place in Africa, where many more species might display this behaviour.
A high proportion of altitudinal migrants are found in areas like the Himalaya, the Andes or the Rockies in western North America. In continental Europe, Wallcreeper, Citril Finch and White-winged Snowfinch are good examples, while in North America many finches, especially the three rosy finch species, head down for the winter. Usually altitudinal migration involves birds which are breeding at the higher elevation, but in Hawaii, Nene breeds at low elevation and migrates higher for the non-breeding season.
There are relatively few altitudinal migrants in Britain as its mountains are not that high, but birds such as European Golden Plover, Eurasian Skylark, Meadow Pipit and Snow Bunting move from higher breeding grounds to lower areas in winter, with some only moving a few kilometres. Dippers may leave high streams and spend the winter on lower rivers, even at the coast or on estuaries, while Grey Wagtails in the Scottish mountains head to the east coast of Scotland or further south to England.
The longest British altitudinal migration is undertaken by a bird that flies south or east to where it breeds: Water
Pipit. This species undergoes an altitudinal movement of a considerable distance, with a few hundred birds from the Alps, Pyrenees and other European mountain ranges heading for southern England and East Anglia. It arrives from mid-October to late November, and stays until the end of
April; peak numbers are often recorded at many sites in early April as birds pass through. Chris Harbard