Friday, June 7, 2013

African traveler - the Marabou Stork

Recently, when catching vultures to fit them with satellite transmitters, we have incidentally caught a number of Marabou Storks – these we tagged before release in order to learn more about their movements. The tags are yellow patagial tags (attached to both wings), and each bird has a unique number engraved in black on its tags. The tags are quite conspicuous as shown in the photograph, but of course they are useless unless people know what to look out for, and to whom sightings should be reported. Information should be sent to Pete Hancock,, including the following details: date, locality (preferably with GPS co-ordinates), and tag number and colour. A digital photo would be very useful as the numbers can often be clearly seen on the image. It would be great if other people would use their networks to spread the word further, as we need wide coverage since we believe that these birds travel as far as central Africa. Why do we think our tagged birds will be seen outside Botswana when most southern African field guides state that the Marabou is resident and nomadic with local movements? Marabou Storks have very few breeding sites in southern Africa, there being a single colony (of about 30 breeding pairs) in Swaziland, while Botswana has the largest breeding population in southern Africa, of a mere 100 pairs. The species does not breed in South Africa or Lesotho, and there are a few minor sites in Namibia and Zimbabwe. Against this background, how does one explain the fact that in Botswana, the Marabou Stork often occurs in congregations of 3,000 to 5,000 birds? Could the relatively few breeding birds be maintaining a population of tens of thousands of storks? Or is it more likely that birds are coming to Botswana from elsewhere? Simple arithmetic, based on a clutch of two to three eggs per pair per annum shows that it would take a long, long time to produce this number of birds; it seems more probable that there is a regular influx of storks from further afield. Information on the movements of Marabou Storks has important implications for their conservation. It is speculated that the central African population in Uganda and Kenya (where the species has its stronghold) may well be providing most of the storks in southern Africa.