Tuco-tucos (Ctenomys aff. knighti) are subterranean rodents that inhabit the Monte desert in  Northwest Argentina. In the laboratory, they show a robust nocturnal pattern of locomotor activity. In the field, however, they are more active during the day. What would be the advantages of the diurnal pattern of activity in the field? In this work, we test the hypothesis that diurnality results in energy savings, since by concentrating the activity during the day,  tuco-tucos can save energy during the colder hours of the night, resting in burrows where the temperatures are higher than on the surface. Our simulations based on metabolic measurements taken in the laboratory and on environmental temperature data suggest that diurnal activity implies energy savings in winter, which, in addition to being the coldest season, is also the season with less food availability. In the summer, the energy savings are low, indicating that, in this season, other factors may be determinant of the temporal activity pattern.

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