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10 July 2006

New Vulture Colour-Marking Method for Southern Africa

by Andre Botha ( Manager: Birds of Prey Working Group)

A new era in the study of the biology of southern African vulture species has arrived with the implementation of a method, known as patagial tagging, in the colour-marking of such birds. Colour-marking of birds is commonly used as a simple and affordable method to identify individuals in a population to determine, among other aspects, the birds” movements, dispersal, foraging range and longevity across their range.

Vultures in southern Africa have been colour-marked for more than 30 years, mostly using plastic colour rings fitted to the birds” legs in a combination of colours unique to each individual. More than 8000 vultures have been ringed using this method over the years. By far the most vultures to have been fitted with colour-rings were Cape Vulture (Gyps coprotheres) nestlings. The intrepid members of the Vulture Study Group were brave enough to abseil down precipitous cliff faces to fit the rings in the nests of these birds at most of their breeding colonies in the region during the seventies and eighties. Colour-ringing was also used on other species such as African Whitebacked Vulture (Gyps africanus), Lappetfaced Vulture (Torgos tracheliotus) and White-headed Vulture (Triginoceps occipitalis), but in much smaller numbers.

The success of any colour-marking effort is measured in the number of birds that are either re-sighted or recovered after being ringed. The re-sighting and recovery rate of vultures fitted with colour rings have been rather low with less than 10% of birds being reported to date. A significant percentage of these birds were carcasses of nestlings recovered below breeding colonies by vulture monitors after the breeding season, and not of free-flying birds seen after dispersal from their natal areas.

Free-flying birds with colour-rings often perched in such a way that the rings were covered by their feathers or obscured by vegetation. Another problem identified was that some birds were quite adept at removing some of the plastic rings from their legs, thereby rendering the colour combination useless. These combinations were also quite difficult for the lay-person to record and the colour of the rings often faded or changed due to the effects of ultra-violet. Despite this, interesting information on bird movements and dispersal were obtained.

Due to the mould for the plastic rings being lost by the manufacturer in 2004, the Birds of Prey Working Group (BoPWG) of the Endangered Wildlife Trust decided to investigate alternative options for the colour-marking of vultures in southern Africa. The option decided on needed to meet the following criteria:

• The proposed system should be simple, user-friendly and facilitate consistent implementation across southern Africa.
• The welfare of the birds should be of paramount importance at all times and should not inhibit its normal life cycle and behaviour.
• The marking method to be used must have a proven track-record of durability, resistance to discoloration and prevent removal thereof by the bird itself.
• The system should be cost-effective and affordable.
• It should facilitate an optimal rate of return with regard to re-sighting and recovery.
• The system must be effectively managed and coordinated.

The testing of the various options was conducted during 2005 and the first quarter of 2006 and involved a number of BoPWG staff, fieldworkers, volunteers and associate organizations who participated in assessing various methods. The options assessed included an up-to-date version of plastic colour rings, two types of PVC rings that could be engraved with specific codes and patagial tagging. Patagial tagging refers to the fitting of a plastic tag to the “patagium”, or frontal flap of skin to the wing of a bird and has been used worldwide with great success on a wide range of bird species, including vultures and condors in Europe and America.