Birds of a Feather
Summer has clearly arrived with downpours of rain, swarms of insects, the sweet smell of flower nectar and the arrival of some early, migratory birds! The mystery of bird migration is one which has perplexed thousands of people for thousands of years. Two thousand years ago, Aristotle believed that swallows hibernated in the mud during winter. One hundred or so years ago, many believed that birds flew to the moon at the end of summer and Cuckoos changed into hawks during the winter! It is fair to say that in more recent years, people have become more understanding about the movements and mechanisms governing bird migrations. By bird tagging and with lab studies there are now more realistic theories regarding non-breeding destinations.
In Southern Africa, there are over 130 bird species which undergo epic migrations either inter-continental or within Africa itself. Constantly on a summer holiday, birds are moving from one extravagant banquet to the next avoiding food shortages and harsh weather conditions. While many bird species have a predictable and defined journey, other migrants have a more random flight pattern which are thus not strictly classed as migration. This can be seen in the Red-billed Quelea which moves in enormous plague-like flocks tracking food supplies along their journey.
Some birds travel over extremely long routes which require planning and preparation. Birds will plot their route taking the most efficient track and taking into consideration the distance, geographical barriers, favourable winds, flying style (flapping or soaring) and planned stop overs for rest and refueling. Larger birds such as the Steppe Buzzard, use funnel shaped migratory patterns to avoid sea crossings and take advantage of the thermals produced over land. These birds will only travel during the day while many other species will only travel at night to preserve energy and make use of the stars for navigation.
Migratory birds have an inherent and learned sense of direction. The Earth produces a magnetic field that varies in angle over its’ surface. Birds are highly sensitive to these fields and are able to align themselves accordingly. Some birds will use the sun as a compass to direct their flight paths and have evolved the ability to compensate for its constantly changing position during the day and through different seasons.
In many parts of the world people have had to learn to share airspace with migratory birds by creating “Bird Plague Zones” which prohibit the use of zones favoured by migratory bird species. These birds face many threats during their journey through habitat loss by human development. In some areas they are made to dodge bullets, avoid traps for birds which are traded, redirect their flight over land covered by industrial waste among many other obstacles.
The Record Holders: The Arctic Tern travels a distance of 50 000km from Arctic tundra to the Antarctic and back. The fastest non-stop journey is taken by the Bar-tailed Godwits migrating from Alaska to New Zealand over the Pacific ocean for 11 600km. The Ruppell’s Vulture is the highest recorded flying bird which was hit by a plane at 11 300m; (Mt Kilimanjaro is 5 895m at the summit).