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This is that time of the year when we are often thrilled by our first sighting of a returning migratory bird species. Already the Wahlberg Eagles are back in early August. As an Intra African migrant they don’t have to travel far and are not away for long.

But many species are not so fortunate and undertake epic journeys across the world every year. What strong urge can provoke such an undertaking? Mostly, it is not one factor alone but a combination of a few. Whether the birds know it or not there are many benefits in migrating.

The obvious reason for moving from one area to another would be to follow a food source much like the wildebeest in East Africa and to a lesser extent the lions that follow them. Other scarce resources like nesting materials and sites can be another underlying reason. Competition is another factor and whether it is from birds within the same species or another species or even from animals it’s definitely a reason why this behaviour has evolved. Predation and parasitism can also be escaped by absenteeism. Extreme weather conditions are an obvious reason for migration and often they bring with them the associated shortages of resources. These perhaps are the underlying benefits of migration but not the triggering factors.

Day-length, temperatures and the angle of the sun’s rays will stimulate migrating birds to begin preparing for the journey and prepare for the journey they do!

Most birds, especially those that attempt non-stop or very long flights, have to build up fat reserves before hand. These fat deposits are a response to hormonal changes that it turn, are a response to environmental changes. Some birds may even double their body weight such is the demand of this hazardous journey. The larger birds like raptors and storks migrate short distances between stop off points and do not need to fatten up before leaving. The Steppe Eagles that come all the way from the Russian Steppes ( Palaearctic-African Migrants) arrive here in November/December. These birds tend to fly over land; they need the warm air of the thermals to fuel their flight as well as the food available only from land. Many of these birds including the Lesser Spotted Eagles, Booted Eagles, Storks and Pelicans fly in huge concentrations over Israel and Gibraltar between their nesting grounds in Eurasia and their non breeding sites in Africa twice a year. Their flight plan is longer than a sea route and man- made factors add extra risk. While most birds fly at altitudes less than 3000 feet, pilots have reported bird sightings as high as 26000 feet.

Flying this high and these distances requires some adaptations. These bird’s bodies and wings tend to be more stream- lined. High flying migrants have specialized haemoglobin (the oxygen carrying red blood cells) that allows them to change altitudes abruptly while ensuring adequate oxygen supply.

During migration many normally diurnal birds choose to fly by night. The advantage being that it is less demanding on energy as the air is calmer and cooler and even denser with less chance of a headwind. The navigation techniques of these species are obviously highly specialised.

As we move into the summer months more and more species will arrive here to take advantage of the prolific food supply. Whether a bird migrates or not, depends largely on what it eats. Migration is common in insect- eating birds with the most common ones being the aerial feeders- the swifts, swallows, bee eaters and nightjars that feed in the open skies. Insects that are hawked out of the open skies are more exposed to the elements and their numbers are conspicuously reduced in the winter months and many of the birds that feed off them, move off to find an alternative. The insects that winter in the protection of the leaf litter and grass cover will continue to provide food for the other birds that feed off them. Out of the Rollers, our Lilac Breasted Roller is a resident insect eater while the heavier European Roller will spend only from early December until March in our part of the world.

Our fish-eating Malachite Kingfisher is resident while the similar Pygmy Kingfisher is an insect eating migrant. The Woodland Kingfishers come from Angola and are a conspicuous insect -eating visitor.

Another fascinating migrating species are many of the cuckoos. The Red Chested Cuckoo, Diederik, Klaas’s, African, Jacobin and many more all come here to breed. This presents the intriguing concept that migratory behaviour is inherited rather than learned when the cuckoo young are raised by foster parents of different non migratory species.

Migration is the seasonal movement from a breeding area to a non- breeding area. It differs tremendously from species to species in the physical demands, the routes, the navigation methods and the potential benefits. It is a survival strategy not only for the individual but also for the species.

While some journeys are a mere hop of a couple thousand kilometres journeys of 10 000km are not unusual while the longest round trip is undertaken every year when the Arctic Tern flies a staggering 50 000 km.

Over 130 bird species in Southern Africa are migrants. The marvels of their skills of navigation and orientation is yet another fascinating aspect of this behaviour , but simply having them show up on our door step is a privilege and a delight to behold.