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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.

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 37.5C. Embryos that regularly cooled to 20C had higher mass-specific metabolic rates than embryos incubated constantly at 37.5C. 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. Disciplines Ornithology | Other Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology | Zoology CommentsThis article is from Physiological and Biochemical Zoology 79 (2006) ABSTRACTFor 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 37.5ЊC. Embryos that regularly cooled to 20ЊC had higher mass-specific metabolic rates than embryos incubated constantly at 37.5ЊC. 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.

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Equations for the calculation of O2 consumption, CO2 production, and water vapor production in a constant-volume, closed-system respirometer are presented. Necessary measurements include only the initial temperature, pressure, and gas volume in the respirometer chamber, and the fractional concentration of O2 in gas samples taken at the beginning and end of the period of measurement. Potential errors resulting from changes in CO2 and water vapor concentrations are identified. Ignoring CO2 effects can produce up to a 6.4% error in estimates of O2 consumption, and errors due to water vapor effects can exceed 100%. Techniques are presented for minimizing potential errors and for measuring CO2 and water vapor concentrations with an O2 analyzer so that potential errors can be eliminated.