Altitudinal migration of KwaZulu-Natal birds.

White-starred robin- Winter visitor to St Lucia

The province of KwaZulu-Natal is often referred to as the ‘tilted province’ because the land rises so sharply from the coast to the escarpment. In a distance of only 170km, one can go from the majestic Drakensberg mountains (3000m or more above sea-level) to the coast. It is because of this unique topography that KwaZulu-Natal experiences a birding phenomenon known as altitudinal migration between March and September each year.

Altitudinal migration refers to the movement of birds from higher altitudes to lower altitudes (or visa versa) according to season. For example, in the winter months the higher altitude locations will become very cold and the numbers of invertebrates will decrease. Insectivorous birds from these higher altitude locations therefore migrate to lower altitudes where it is warmer and insect life is more plentiful.

At least 76 species of birds are altitudinal migrants in KwaZulu-Natal (Johnson & Maclean, 1994).

Some of the altitudinal migrants only move short distances down the slopes of the escarpment to temporarily escape extreme weather conditions whereas others move from the mountains/escarpment all the way to the coast to take advantage of the warm maritime climate for the entire winter.

Examples of altitudinal migrants that visit St Lucia in the winter months include: Spotted ground-thrush, White-starred robin, Grey cuckoo-shrike, Chorister robin-chat and Common stonechat. Furthermore, some species of bird which are resident all year round (for example Red-capped robin-chat) become much more plentiful in the winter because many of their compatriots from higher altitudes join them at lower altitudes.
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Why then, you may ask, do these birds not just stay put on the coast year round? The reason is breeding; the birds migrate back to higher altitudes in the spring to look for territory to breed. The higher they go, the stronger the likelihood of finding an unoccupied patch of suitable habitat.

References
Johnson, D.N. & Maclean, G.L. 1994. Altitudinal migration in Natal. Ostrich 65:86-94.

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