Fig. 4.

Quantification of the energetic benefit of diurnality. (A) Daily variation in average September surface and nest temperatures. The nest temperature is buffered from the surface temperature by nest insulation leading to a later peak phase and reduced amplitude. The expected nest temperature is calculated based on the nest insulation constant measured for mouse nests in our outdoor mouse enclosures. (B) Scholander curves showing the relation between T_a and energy expenditure for the rest and active phase of WFF mice. (C) Calculated daily energy expenditure decreases with increasing daytime activity for mice subjected to natural daily temperature cycles. Daily energy expenditure varies between 60.7 and 55.4 kJ/day. (Insets) The encountered temperatures for a completely nocturnal (Left) and diurnal (Right) mouse. Due to the buffered nest temperature, compared with nocturnal mice, diurnal mice encounter higher temperatures during both their active and rest phase.