Differential scaling of home-range area to daily movement distance in two African tortoises

Movements of the tortoises Geochelone pardalis (mean body mass 4.0 kg) and Kinixys spekii (0.62 kg) were studied by thread-trailing. The mean daily movement distance of G. pardalis was 435 m, and the short-term home-range area was 26 ha. The values for K. spekii were 172 m and 1.9 ha, respectively. The area used by G. pardalis was significantly larger than would be produced by scaling up the movements of K. spekii in the same geometric pattern. Home-range areas were about the same size (K. spekii) or several times as large (G. pardalis) as those predicted for mammals of equal body mass. Ingestion of soil for sodium may be a factor determining the large home range of the purely herbivorous G. pardalis. These tortoises frequented a small area of strongly sodic soil from which they dispersed over long distances.