Techniques for determining movement patterns of Blue and Wattled Cranes in South Africa - colour-ringing versus satellite telemetry

摘要

Knowledge about the annual movement patterns of endangered species is important in understanding various aspects of their biology, such as dispersal from natal areas, seasonal movements,and areas where large numbers aggregate. We compare two techniques of determining and analysing crane movement patterns in South Africa's threatened crane species, namely colour-ringing and satellite telemetry. Wattled Crane and Blue Crane colour-ringing began in 1987 and 1993 respectively. This technique, although being labour-intensive and time-consuming, has produced valuable information about Wattled Crane movements in the eastern parts of the country, with resightings of 42% of the ringed Wattled Cranes. Since 1993,296 Blue Crane have been ringed but in contrast to the Wattled Crane, the resightings have not added much to our knowledge of this species' movement patterns. The Blue Crane, being endemic to southern Africa and termed a local migrant, required a more sophisticated technique for elucidating Blue Crane movements. Between 1996 and 1999, ten Blue Cranes were fitted with satellite transmitters in four different provinces. The transmitters battery life lasted for an average of 333 days (range: 182-707 days) giving an average of 118 fixes per transmitter life. However, of these fixes an average of only 27 points per transmitter (22.9% of the points) were usable, i.e. had a sufficiently accurate rating and thus provided the coordinates locating the bird to the nearest kilometre. Therefore, the selection of the appropriate technique for a movement study should dependent on the specific life history and behaviour of the particular species, as both techniques have merits, depending on your needs and financial resources. Despite being time-consuming and labour-intensive, colour-ringing was by far the more accurate technique in identifying movement patterns of the Wattled Crane, while satellite telemetry, although providing surprisingly inaccurate data at a high expense (a serious consideration for African conservation work) is a consideration in species with long-distance movements. However, in a large population such as the Blue Crane in South Africa, and the short migratory distances this species undertakes it is more suitable to utilise the colour ringing technique to track movement patterns.