Variation in the daily activity, movement and refugia of Critically Endangered geometric tortoises,Psammobates geometricus, in autumn and spring

Abstract

To help assess habitat requirements of Critically Endangered geometric tortoises, we used thread-trailing to measure daily activity, movements and refugia of adult Psammobates geometricus in autumn and spring 2002. We found strong differences between seasons, and effects of weather, individuals and sex. The high activity was consistent with mild weather during autumn and spring. However, daily temperatures limited female movements on cool autumn days and male movements on warm spring days, a pattern consistent with sexual size dimorphism (large females and small males). The long movements in autumn probably helped tortoises find food plants that grow quickly after autumn rains; both sexes recover body condition from autumn lows, and females begin egg production in late-autumn and winter. These movements may also help males mate with females before they ovulate. The high activity of females in spring should help them forage and sustain their vitellogenesis, egg production and nesting in spring. Male paths tended to be more linear than female paths in both seasons, so this sexual difference is likely not linked to food consumption. Males may move long, linear paths to engage females and avoid other males. Males may have been thermally-challenged in spring. Their movements decreased with increased ground temperatures (in the sun), they used denser refugia in spring than in autumn, and in spring used denser refugia than females used. Geometric tortoises typically used different refugia on consecutive nights, a type of predator avoidance mechanism.

Population Structure and Sexual Dimorphism in a Southern Population of Tent Tortoises (Psammobates tentorius tentorius) of the Karoo, South Africa

“…Consequently, females must assimilate more nutrients, or allocate nutrients differently, than do males. This size pattern seems consistent with that of the congener, P. geometricus (Henen et al 2017), which inhabits more mesic habitat. A larger female size for both species likely accommodates the much larger gametes females must create, compared with that of males, and the digestion to support the vitellogenesis, egg formation, and nesting (see also Bonnet et al 2001, among others).…”

“…The smaller body size and larger shell openings of males may be part of an adaptation to a mating strategy employed by this species (see also Bonnet et al 2001; Leuteritz and Gantz 2013). Small size may enable greater mobility and search distances by males, which may aid to the search for females, refugia from weather and predators (e.g., Henen et al 2017), and ability to disperse (Berry and Shine 1980; Bonnet et al 2010). Male P. t. tentorius would actively seek mates.…”

Nonchalant neighbours: Space use and overlap of the critically endangered elongated tortoise

“…Rainfall likely boosts resources, thus triggering opportunistic reproductive activity (i.e., mate searching, mate competition, and copulation), as has been documented in other vertebrate species (Hau, 2001;McNamara, Barta, Klaassen, & Bauer, 2011;Tökölyi, McNamara, Houston, & Barta, 2012). The female tortoises' peak activity during the wet season is likely due to the influx in available resources (Collins et al, 2014), and potentially nesting activity (Lagarde et al, 2002;Henen, van Bloemestein, Hofmeyr, & Weatherby, 2017).…”

The Effect of Size on Postrelease Survival of Head-Started Mojave Desert Tortoises

“…Moving between or relocating to different burrows requires tortoises to be surface active; therefore, the number of burrows used by an individual may be negatively associated with survival. Alternatively, burrow switching may be a form of predator avoidance (Henen et al 2017), with greater survival probability associated with individuals that use this strategy. Thus, both the tendency to be surface active and variation in burrow switching behavior may be important predictors of postrelease survival.…”