By Leon Marshall
Reports about openbilled storks appearing in places they had never been seen before in South Africa were hesitant at first. The birding fraternity is notoriously sceptical of claims about unusual sightings and amateurs are wary of incurring their derision.
But then the floodgates opened. People reported seeing them all over, even as far as a thousand miles away from their normal range.
Photo by by Mark Anderson/BirdLife South Africa
One regular birder in the country’s southern extreme wrote in a letter to a magazine that he was so surprised at seeing the birds on a river bank there that he hit a sand bank with his rubber dinghy and went flying.
Theories abounded. Climate change was quickly held to blame. Some hinted at darker forces being at work. This probably had something to do with the mythologies attached to these types of birds, such as that white storks bring babies. It could also be because of their unnerving habit of standing still for such long periods, as if deep in thought, or of the way they stride with slow, measured step through the shallows.
The birds are dark in colour, and the odd shape of their long beaks, which have a pronounced opening towards the front through which the daylight shines, adds to their weirdness. The openings have a useful purpose, though. Snails are a favorite of theirs, and they use the gap to get a grip on them and crack their shells like a nutcracker.
In South Africa, openbill storks (Anastomus lamelligerus), or African openbills, as they are also known, are usually restricted to Kruger National Park on the country’s north-eastern border with Mozambique and along a strip down to its Indian Ocean coast north of Durban.
Botswana’s Okavango Swamps are a favorite stomping ground, and from there further up the continent they occur widely in sub-Saharan countries like Zimbabwe, Zambia, and Angola.
Their unusual occurrence started to be reported at the start of South Africa’s summer season, in December. It happened mainly on SAbirdnet, an internet forum on which birders post their sightings and exchange information. Soon the phenomenon was being reported in newspaper and on radio.
Some speculation put it down to changes that might have caused the birds’ floodplain and marsh habitats to disappear, possibly because of weather changes or through farming practices, or other human developments.
It was suggested that the random use of pesticides in their home ranges might have killed off the mussels, molluscs and snails on which they live.
Mark Anderson, executive director of BirdLife South Africa, a partner of BirdLife International, avoided venturing a firm opinion as to the likely causes of the shift when asked about it on radio, saying there could be many factors at work that needed probing.
A similarly cautious approach was taken by his fellow scientists, Peter Ryan and Phil Hockey, co-authors of the bulky seventh edition of the authoritative Roberts Birds of Southern Africa that was published in 2005.
Writing in Africa Geographic Birds & Birding magazine, they say that such rapid range changes are called “irruptions”. They occur fairly regularly at high latitudes where severe temperatures drive species to warmer climes, but are less frequent in Africa, where they tend to be tied to rainfall.
Irruptions often involve young, naïve birds, but in the case of the openbills, adults and juveniles were involved. As there are only about a hundred or so breeding pairs that keep in the northern parts of South Africa, the large number of birds that cropped up farther south suggest they came from further north.
“But quite where is unknown. Vast numbers breed in Zambia in winter and the timing of the irruption suggests that they could be birds dispersing from these colonies after breeding,” Ryan and Hockey wrote.
One possible explanation they offered was the invasion of Zambia’s Kafue Flats by a thorny shrub, Mimosa pigra, that flourishes on seasonally inundated land. It got there in the 1980s and by 2005 it had already covered more than 7,000 acres (2,832 hectares).
In 1970 about 500,000 openbills were counted on the Flats. But recent surveys have shown that areas infested with the South American shrub support just about one percent of the number of the birds compared to pristine floodplain.
The authors conclude that it may well be deteriorating environmental conditions that are driving the birds south.
Nat Geo News Watch contributing editor Leon Marshall is an environmental writer in South Africa. A leading political journalist and executive editor for Africa’s largest newspaper group for years, he has won numerous awards, including a 2004 Reuters-IUCN Media Award for Excellence in Environmental Reporting. Leon has covered climate change from a global and African perspective, having attended conferences on the issue in many parts of the world. He has written extensively on the ambitious transfrontier-parks program of the sub-continent and is now writing a book on the subject.