Saturday, January 26, 2013

Whose vulture is this?

Satellite tracking of birds is an expensive undertaking, but the results are invariably worth the cost. This has proved to be the case with a joint project being undertaken by BirdLife Botswana in partnership with CKGR Research and the Denver Zoological Foundation. The project aims to determine the movements of Lappet-faced Vultures in Botswana, specifically to ascertain whether the birds are able to meet their year-round requirements in Botswana’s large protected areas, or whether they scavenge in areas where they could be susceptible to poisoning by humans. The project is in its early stages, but to date we have captured five adult Lappet-faced Vultures using a cannon net, and attached satellite transmitters to all five – four in the Central Kalahari and one in the Makgadikgadi. The precise positions of the birds are recorded every two hours during the day, and initially it was clear that most of them were breeding as they remained in a fairly prescribed area around specific points which we presumed were their nests. Since the end of November, their home ranges have been expanding rapidly, and some spectacular movements have been undertaken. One particular bird made a long-distance foray into southern Namibia, and then returned a few days later, as shown on the map below.
It is important to note that the vulture flew southwest along the upper, slightly irregular route, and returned via the bottom route – which is incredibly straight, as though the bird was in a hurry to return and unerringly took the most linear course! The directness of this line-of-flight is uncanny – it would require a GPS or other navigational aid for a human to achieve this degree of precision! Apart from this feature, the 1,500 kilometre venture also raises some other interesting questions: Was this a deliberate sortie to a predetermined point for a specific purpose? What is at the place in Namibia where it turned around? Why did it return to its point of departure? It seems reasonable to believe that the foray was not accidental; wind direction is prevailingly from the east, and would have aided the bird on the outgoing leg of its journey, but hindered it on its return. It is clearly not being blown randomly throughout the region! When I asked Namibian colleagues what was at the turning point where the bird spent a short while before flying home, Chris Brown, Director of the Sustainable Solutions Trust and ornithologist of note, had the following information: “The map below shows the movement pattern, over more than five years, of a young Cape Vulture fitted with a satellite transmitter captured near Otjiwarongo by Maria Diekmann.
You will notice that the bird spent a lot of time in the Kalahari of south-eastern Namibia, in the same general area as your Lappet-faced Vulture. I went down there one weekend and spoke to the Manager of one of our Gondwana Parks/Lodges, Jaco Visser. Jaco grew up on a farm in the area and knows the farmers and their land uses. We had the specific farms on which the birds spent most time. Jaco immediately recognised these farms, not as game farms, but as commercial livestock farms where the farmers were well known to be poor farmers who regularly suffered high livestock mortalities. Most were sheep and goat farmers. I guess that, over time, these farms become areas well know to the vultures as profitable searching grounds and they keep an eye on what is happening there. The info system of vultures seems to operate at a SADC level!” This definitely adds another piece to the puzzle! It is apparently no coincidence that our bird should go down to the south-eastern part of Namibia to see what, if anything, was on offer there! The picture now emerging is as follows: Lappet-faced Vultures know all the good foraging areas in southern Africa, and it is quite simple for one of them to make a 1,500 kilometre round-trip to one of these locations to assess its current potential as a food source. A direct flight of 1,000 kilometres from the Central Kalahari could put a vulture in any one of seven southern African countries! Another Namibian colleague, John Mendelsohn, who was involved in monitoring the travels of several Cape Vultures said that ”Perhaps the most remarkable finding or all is that these birds avoided the Kgalagadi Transfrontier Park, rarely even crossing over its border for a sniff or look-see”. The information above immediately answers our fundamental research question about Lappet-faced Vultures: there is no protected area in southern Africa which is large enough to provide safety for this species from the potential dangers imposed by humans. In fact, the scenario is worse than ever anticipated – a single poisoning incident could annihilate a very large segment of the populations of all southern African vulture species, Lappet-faced included.

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