Revista Chilena de Historia Natural 75 (1): 149-156, 2002
RESEARCH ARTICLE
A time-energy analysis of daytime surface activity in degus, Octodon
degus
We present an analysis of time and energy allocation in a day-active caviomorph rodent,
the degu, Octodon degus, in central Chile. We quantified components of surface activity in the field on a daily basis in
individual degus near the time of the summer solstice, when conditions of heat and aridity were also at a seasonal extreme, in order to
answer the following questions. Does the absolute time available for surface activity limit performance? Does the allocation of time and
energy for locomotion place a functionally significant limitation on overall energy balance and performance? Degus spent about 2/3 of
their above-ground time foraging; they remained stationary about 88 % of the time, walked around slowly about 10 %, and were running
rapidly from one point to another only about 2 % of the time. Net locomotion costs (for walking and running combined) were computed
to be only 2.2 % of total daily energy expenditure. This low net allocation of time and energy to locomotion, taken together with abundant
distribution of plant food over the extremely small home range, suggests that the daily performance of degus is not limited by the
absolute amount of time available under normal conditions at the summer solstice (seasonal extreme of day length, heat, and aridity).
Total energy demands can be met by as little as 4.5 h surface activity per day. Our empirical observations, together with a simple
computational model of time and energy expenditure, provide a useful validation of the impact of activity on the overall energy balance
of a free-living rodent. The small impact of locomotion on the total energy budget is an economy of the behavior of these animals, and
the rapid mode of locomotion allows them to minimize predation risks. We believe that this kind of quantitative analysis of energy
expenditure associated with behavior in the field can contribute a useful basis for theoretically based time-energy
modeling.
Key words:
time, energy, activity,
central Chile
