Burrow structure and foraging costs in the fossorial rodent, Thomomys bottae

Abstract

A model for calculating the energy cost of burrowing by fossorial rodents is presented and used to examine the energetics of foraging by burrowing. The pocket gopher Thomomys bottae (Rodentia: Geomyidae) digs burrows for access to food. Feeding tunnels of Thomomys are broken into segments by laterals to the surface that are used to dispose of excavated soil. Energy cost of burrowing depends on both soil type and on burrow structure, defined by the length of burrow segments, angle of ascent of laterals, depth of feeding tunnels, and burrow diameter. In a desert scrub habitat, Thomomys adjust burrow segment length to minimize cost of burrowing. Observed segment lengths (mean=1.33 m) closely approximate the minimum-cost segment length of 1.22 m. Minimizing energy expended per meter of tunnel constructed maximizes efficiency of foraging by burrowing in the desert scrub. Burrow diameter and cost of burrowing increase with body size, while benefits do not, so foraging by burrowing becomes less enconomical as body size increases. Maximum possible body size of fossorial mammals depends on habitat productivity and energy cost of burrowing in local soils.

The Influence of Foraging Mode and Arid Adaptation on the Basal Metabolic Rates of Burrowing Mammals

“…The cost-of-burrowing hypothesis suggests that reduced BMR may compensate for the enormous energetic demands of subterranean foraging (Vleck 1979(Vleck , 1981. The thermal-stress hypothesis proposes that reduced BMR may minimise the chance of overheating in closed burrow systems where evaporative water loss and convective cooling are substantially reduced (McNab 1966(McNab , 1979b.…”

“…The cost-of-burrowing hypothesis (Vleck 1979(Vleck , 1981 proposes that fossorial mammals have a reduced BMR to compensate for the enormous energetic demands of subterranean foraging. Logical extension of this idea leads to the hypothesis that fossorial animals should have lower BMRs than semifossorial animals.…”

“…Saccostomus campestris) forage on the surface and construct burrow refuges that may be used for caching food, reproduction, and so forth, whereas truly fossorial animals (e.g., pocket gophers Thomomys bottae) live and forage entirely beneath the surface (McNab 1979b;Nevo 1979). Generally, semifossorial species construct relatively short, structurally simple burrow systems, whereas those excavated by fossorial animals are longer, more complex, and represent a much more substantial energetic investment (Vleck 1979(Vleck , 1981.…”

Influence of spatial environment on maze learning in an African mole-rat

“…Efficient spatial orientation and memory is, however, critical for fossorial species in their search for food patches or mates, as underground locomotion and excavation is comparatively expensive (Lovegrove 1989;Vleck 1979Vleck , 1981Zelová et al 2010). In the absence of light, subterranean species use olfactory (Heth et al 2002) and somatosensory stimuli (Kimchi and Terkel 2004b), as well as the earth's magnetic field (Burda et al 1990b;Kimchi and Terkel 2004a) and path integration (Kimchi and Terkel 2002), to orientate themselves.…”

“…Mole-rats dig their own tunnel systems, with the diameter of the tunnels closely approximating the size of their cylindrical bodies (Bennett and Faulkes 2000), while leaving space for animals to turn around in tunnels (White 2005). This not only keeps excavation costs down (Vleck 1979(Vleck , 1981, but ensures close contact between the sensory hairs on the animal's body and the wall of the tunnel (Burda et al 1990a;Kimchi and Terkel 2004b). Subterranean animals are very dependent on somatosensory input in their spatial orientation.…”