David Vleck

The Energy Cost of Burrowing by the Pocket Gopher Thomomys bottae

Thomomys bottae maintain body temperature (Tb) at 36 ± 0.3 C at ambient temperatures (Ta) between 5 and 25 C. At Ta greater than 25 C Tb increases with Ta. Rate of oxygen consumption at Ta below 25 C is described by the equation: V̇o2 (cm3/g·h) = 2.52–0.062 Ta. Minimum resting oxygen consumption is 0.84 ± 0.16 cm3/g·h and occurs at Ta between 28 and 30 C. Oxygen consumption during burrowing was measured in four different soil types and a cost-of-burrowing model developed to fit these data. The model can be used to estimate the energy devoted to burrowing by free-living pocket gophers. Energy cost of burrowing varies with soil density and cohesiveness, burrow size, and burrow structure. Depending on soil type, burrowing can require 360–3,400 times as much energy as moving the same distance across the surface. The high energy cost of burrowing suggests that energy conservation may be particularly important to fossorial animals. The low basal metabolic rates and thermal conductance can be viewed as adaptations to conserve energy rather than adaptations to heat stress. The cost-of-burrowing model should be generally applicable to other fossorial rodents.

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

SummaryA 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.

Periodic cooling of bird eggs reduces embryonic growth efficiency.

For many bird embryos, periodic cooling occurs when the incubating adult leaves the nest to forage, but the effects of periodic cooling on embryo growth, yolk use, and metabolism are poorly known. To address this question, we conducted incubation experiments on eggs of zebra finches (Taeniopygia guttata) that were frequently cooled and then rewarmed or were allowed to develop at a constant temperature. After 12 d of incubation, embryo mass and yolk reserves were less in eggs that experienced periodic cooling than in controls incubated constantly at 37.5°C. Embryos that regularly cooled to 20°C had higher mass‐specific metabolic rates than embryos incubated constantly at 37.5°C. Periodic cooling delayed development and increased metabolic costs, reducing the efficiency with which egg nutrients were converted into embryo tissue. Avian embryos can tolerate periodic cooling, possibly by adjusting their physiology to variable thermal conditions, but at a cost to growth efficiency as well as rate of development. This reduction in embryo growth efficiency adds a new dimension to the fitness consequences of variation in adult nest attentiveness.

Metabolism of Avian Embryos: Patterns in Altricial and Precocial Birds

We measured rate of oxygen consumption

Metabolism of Avian Embryos: Ontogeny and Temperature Effects in the Ostrich

(\dot{V}_{O_{2}})

Energetics of Embryonic Development in the Megapode Birds, Mallee Fowl Leipoa Ocellata and Brush Turkey Alectura lathami

of individual eggs in five species of birds. The pattern of oxygen consumption during development differs markedly between altricial and precocial species. The

Gas exchange in the incubation mounds of megapode birds

(\dot{V}_{O_{2}})