Small Vernal Home Ranges in the Namaqualand Speckled Tortoise, Homopus signatus
In some herbivores, home range size is correlated negatively with the primary productivity of their environments. Although the South African Succulent Karoo is arid, it receives relatively predictable winter rainfall and therefore relatively predictable primary production toward the following spring. Lush springs may alternate with occasional drought years. Over five spring seasons with variable rainfall patterns, I studied home range size in 21 male and 31 female Namaqualand Speckled Tortoises (Homopus signatus) in the Succulent Karoo using opportunistic sightings, thread-trailing, and radio telemetry. In addition, daily movement distances were determined for 8 males and 28 females with the use of thread-trailing over three spring seasons. The average home range size for H. signatus was 3,470 m2, much smaller than home ranges for tortoises in other arid regions. Home range size did not differ between the sexes, but was negatively correlated with rainfall. Daily movement distances were also similar between sexes, but tortoises moved greater distances in a relatively warm spring. It appears that temporary mesic conditions in spring enable male and female H. signatus to meet their nutritional needs in a relatively small area, and the flexible response to variable environmental conditions may enhance tortoise survival during drought years.Abstract
Average home range sizes (±SD) for Homopus signatus that had at least eight GPS positions within one or more spring seasons from 2000 to 2004. Numbers in bars represent sample sizes. Differences among years were not significant.
Average daily movement distances (±SD) in active male and female Homopus signatus for 174 24-h thread-trailing observations in spring 2000–2002. Numbers in bars represent sample sizes after averaging data for tortoises that had multiple observations. Differences between sexes were not significant, but 2002 had larger daily movement distances than 2000 and 2001.
