|Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
The overwhelming majority of White Storks in southern Africa belong to the migratory population that breeds in eastern Europe and southwestern Asia. At the beginning of the 20th century there were storks breeding on buildings or trees in many villages throughout its range. A variety of factors lead to their decline: the intensification of agriculture in most of western Europe resulted in loss of habitat, droughts in the Sahel impacted severely on the western European population, because this is their non-breeding areas; in some part of Europe, persecution was also a factor. During the 20th century, several countries in Europe lost virtually every breeding pair.
An enormous amount of effort has been invested in improving the conservation status of these charismatic birds. A huge amount of effort has been devoted to protecting the species, and there have been re-introduction programmes in France, Switzerland and the Netherlands. The consensus at the end of the 20th century was that the decrease had been halted, and that storks in western Europe were on the increase. The most important factor in this increase is, unfortunately, not attributable to the efforts of conservationists; the storks have adapted to new habitat conditions in Spain, and now feed on rubbish dumps, and at irrigated fields of rice, lucerne and other crops. In addition, there has, over recent years, been more rain in the west African nonbreeding area in the Sahel. In most countries in eastern Europe (Poland, the Baltic Sea states, Ukraine and Russia), numbers of White Storks are also increasing. The population is currently estimated to be 650 000 in eastern Europe and 150 000 in western Europe.
White Storks leave Europe either over Gibraltar or Istanbul, mostly in August and September. The earliest flocks of migrants have large proportions of young birds. Flocks of adults tend to migtrate 10 to 14 days after the young birds. The Atlas of Southern African Birds shows that White Storks arrive in Zimbabwe from about October. They then slowly move south so that peak arrival month in the Western Cape is in December. Most birds leave the region in February and March. These migrants do not breed in southern Africa.
However, and mysteriously, a tiny number of White Storks do breed in South Africa. There are independent records of birds starting to breed in four different localities at different times over the past 70 years.
On 18 November 1940, Dr Austin Roberts found a White Stork nest with three young in a dead eucalyptus tree alongside the main road from Calitzdorp to Oudtshoorn, in the Little Karoo, 400 km east of Cape Town. The farmer told him that "the birds had nested there for at least seven years, as long as he had occupied the farm." During the 1941 breeding season, the tree collapsed, and the five nestlings of the year died. The farmer subsequently erected a nest site, but the storks did not use it. These reports were published in 1941 and 1942 in the journal Ostrich. They were written by Austin Roberts, the country’s leading ornithologist at the time, who had just produced the original (1940) edition of Roberts’ Birds of South Africa.
The second major "outbreak" of breeding has taken place in the Bredasdorp region, just 25 km from the southern tip of Africa at Cape Agulhas, and 200 km east of Cape Town. Breeding was first observed by ornithologists in November 1961, although the farmer reported that they had been breeding there for "some years". The largest number of nests recorded in a single year was four; this number was recorded in 1967, 1974 and 1989. Unfortunately, there is a gap in the monitoring record between 1975 and 1988, but it seems likely that breeding has occurred every year since 1961. Since 1992, only a single pair has been observed breeding each year.
One pair nested on a farm between Albertinia and Mossel Bay, 370 km east of Cape Town. This nest was only 50 m from a main railway line, and the nest was in use for five or six years prior to its "discovery" by ornithologists in January 1966. The nest collapsed in 1971, and the birds moved to a nest platform which was erected close by. The storks continued nesting until 1976. In 1977 and in 1978, only one stork was present at the nest. After that it never returned.
In the early 1970s, some large clutches in Bredasdorp were reduced to manageable proportions by rearing "surplus" chicks at Tygerberg Zoo, just outside Cape Town. This was done to enable the late Professor Gerry Broekhuysen, who had a special interest in these storks, to study them and observe their behaviour. In late 1974, some wild storks started to spend time at the zoo, and sometimes joined the captive flock. In January 1975, a wild pair started building a nest on a bird cage near the stork enclosure. This nest was blown away by a gale force wind. In February the birds built a new nest, "on top of the wire fence of the lion cage". This pair remained at the zoo when the migrants departed in late March. Unfortunately, little has been published about the White Storks breeding at the Tygerberg Zoo over the next quarter century. But in 2000 there are five pairs of free-flying wild storks nesting at the zoo, and there have been at least three or four nests at the zoo for several years.
The big question in relation to the White Storks breeding in the Western Cape is "Where do the offspring go?" Usually, the adults remain in the vicinity of the nest site through the winter, but the young birds typically disappear. Many of the chicks that fledged from the nests near Bredasdorp were ringed. The results from the ringing provided clues which are tantalizing. One bird was recovered close to the Zambia-Tanzania border, and one was recovered in the Free State. Both these recoveries were nestlings from the original 1961 nest.
Another interesting question relates to the relationship between European and South African White Storks. This will be studied through DNA research. We will also be doing intensive counts of White Storks in the district of the Tygerberg Zoo; this will provide important quantitative information about the timing of northwards migration.
It is against this background that a team of ornithologists from the Vogelwarte Radolfzell of the Max Planck Institute in Germany and the Belgische Natuur- en Vogelreservaten (BirdLife Belgium) traveled to Cape Town in November-December 2000. In a collaborative project with the Avian Demography Unit at the University of Cape Town, they placed satellite transmitters on five of the year’s fledglings. Four satellite tags were attached to nestlings at the Tygerberg Zoo near Cape Town. (These are genuinely wild birds, which have chosen to breed at the zoo, and are not "zoo" birds!). The first tag was put on "Tiger" on Friday 1 December 2000, the largest nestling in any of the five nests at the Tygerberg Zoo near Cape Town on this date. The following week, three tags were placed on "Misty" and "Leo", whose nest was on top of the panther's cage, and on "Saturn", who grew up above the giant tortoises. The fifth tag was placed on the largest nestling in the last remaining nest in the Bredasdorp district; this bird we named "Rembrandt", the artist of the Nachtwacht.
The project has the approval of the Western Cape Nature Conservation Board. As was the case with the three satellite-tagged penguins, Peter, Pamela and Percy, that swam from Port Elizabeth to Cape Town in July 2000, the ADU website is reporting the progress of the famous five. The positions of the storks will be updated regularly.
At the time the birds were tagged we wrote. "The harsh reality is that the first few weeks and months out of the nest are extremely hazardous for a young bird. It is likely that several (or even all) of the five young birds will die before they move any great distance. We will do our best to find dead birds, and try to determine the cause of death. Knowing the factors that underlie mortality is an important first step in being able to develop mitigating measures to reduce them." We were lucky; the five birds had fledged successfully, and by 21 January 2001, all were outside the borders of the Western Cape.