Annual bird migration one of nature’s wonders

World Migratory Bird Day is celebrated in the second week of May each year. It is an awareness-raising campaign highlighting the need for the protection of migratory birds and their habitats and is focused on the Eurasian and African flyways.

Birds migrate to find the best ecological conditions and habitats for feeding, breeding and raising their young. When changes in season make conditions at breeding sites unfavourable, migratory birds fly to regions where conditions are better, some flying distances of hundreds and thousands of kilometres.

Many different migration patterns occur throughout the world. While the majority of birds migrate from northern summer breeding areas to wintering grounds in the south,some  birds breed in southern Africa and migrate to northern wintering grounds. Others may migrate horizontally, to enjoy milder coastal climates in winter or by altitude, moving higher up a mountain in summer, and inhabiting lower lying areas during the winter months.

Of about 1 800 bird species found in sub-Saharan Africa, nearly 200 species migrate seasonally between Eurasia and sub-Saharan Africa. A further 50 or so migrate between Africa and the Americas, Antarctica and oceanic islands. In addition, more than 580 species are known to undertake seasonal migrations within the continent.

We are lucky enough in Durban to have a yearly migration event happen on our doorstep. The Barn Swallow (Hirundo rustica) is a Palaearctic-breeding summer migrant that visits our country yearly. This means that it breeds in the Palaearctic region (Europe, northern Asia and North America) during the northern hemisphere summer and then migrates south to take advantage of the southern hemisphere summer. 

About 30km north of Durban, the reedbeds surrounding the small settlement of Mount Moreland (near King Shaka International Airport) play stage to the spectacular arrival of thousands upon millions of Barn Swallows, which roost in the Phragmites reedbeds. These wetlands play an important function as a stopover for the swallows en route to other parts of South Africa and as a staging point before their migration back to Europe. 

This is the largest single roost of Barn Swallows in South Africa and during the months of October to April, the initial small flocks peak at an estimated three million individuals, approximately 0.5% of the estimated global population. The reedbeds are supported by wetlands locally known as Lake Victoria and Froggy Pond, and visitors are welcome to visit the viewing site during the migration. A small fee of R10 per person is charged, which contributes to the upkeep of the view sites.

Migratory birds have the perfect morphology and physiology that enables them to fly fast and across long distances. However, their journey is often exhausting and during which they are pushed to their limits. For example the Red Knot (Calidris canutus) is a wader weighing around 220 g which breeds in the high Arctic tundra and overwinters on the west coast of Africa including South Africa. During its migration it loses nearly half of its body weight with birds weighing around 130g when arriving in South Africa. 

Migratory birds therefore rarely fly non-stop to their destination but stop off frequently to rest and feed, or to sit out a spell of bad weather.

Migration is a perilous journey that exposes birds to a wide range of threats, from natural predation and adverse weather, to man-made threats such as windfarms, powerlines, exposure to poisons and pesticides, and habitat destruction. Loss of habitat due to pollution, degradation or destruction for development, agriculture, grazing or mining, is the main threat facing migrating birds, as they depend on finding suitable breeding and wintering grounds as well as stopover sites along their flyways to rest and feed. 

The loss of any of these sites used by the birds during their annual cycle could have a dramatic impact on their survival.

The human use of land has a direct impact on migratory bird populations. Many aspects of human land use are extremely damaging to the birds’ habitats. For example, urbanisation and intensive agriculture fragment and replace complex networks of natural habitats. Deforestation, afforestation and mining destroy habitat along the birds’ annual migration paths and man-made obstacles such as rotating wind turbines, powerlines, tall buildings and reflecting glass windows, cause barriers to movement. 

These are only a few examples and often a substantial decrease in population numbers within a species is as the result of a combination of such factors. While human development depends on transformations of natural areas, a sustainable use of land is vital to reduce the impacts on our natural resources, such as water, soil, nutrients, plants and animals.

Attention must be given to the careful future planning of human land use, which must be guided by strategic conservation planning. It is important to understand migratory flyways and how migratory bird populations are affected by changes in land use. Even in an urban or industrial landscape, patches of natural habitat, especially wetland areas can provide vital stop-over refuges for migratory birds. 

Careful consideration must be given to all sites when considering the impacts of development and solutions can be achieved through practical mitigation that will benefit both human expansion and conservation of our natural resources.

**Robyn Phillips is a senior specialist at GIBB.

**GIBB is a leading multi-disciplinary black-owned engineering consulting firm based in South Africa. It provides infrastructure planning, design and delivery solutions in Africa, using best-practices and its know how on the continent. Its environmental sector offers solution-based services in Environmental Impact Assessment and Authorisation, sustainability and strategic planning, environmental auditing, waste management, and specialised services in environmental monitoring and biophysical studies. It aims to promote environmental sustainability, ensure legislative compliance and offer world-class environmental solutions to our clients.

References and further reading:

BirdLife South Africa website: http://www.birdlife.org.za/

Mount Moreland Barn Swallows official site: http://barnswallow.co.za/

Turpie J. (1996): Superpilots – Bird migration in Africa, Africa Birds and Birding, June/July, 61-67.

World Migratory Bird Day Website (2017): http://www.worldmigratorybirdday.org